The article describes a very simple homemade emergency light circuit that can be used during power failures and outdoors where any other source of power might be unavailable.
The circuit uses LEDs instead of incandescent lamp, thus making the unit very power efficient and brighter with its light output. Moreover, the circuit employs a very innovative concept especially devised by me which further enhances the economical feature of the unit.
Let’s learn the concept and the circuit more closely:
What an LED Requires to Illuminate Optimally
The concept: We know that LEDs require a certain fixed forward voltage drop to become illuminated and it is at this rating when the LED is at it’s best, that is voltages which is around its forward voltage drop facilitates the device to operate in the most efficient way.
As this voltage is increased, the LED starts drawing more current, rather dissipating extra current by getting heated up itself and also through the resistor which also gets heated up in the process of limiting the extra current.
Increasing LED Efficiency
If we could maintain a voltage around an LED near to its rated forward voltage, we could use it more efficiently.
That’s exactly what I have tried to fix in the circuit. Since the battery used here is a 6 volt battery, means this source is a bit higher than the forward voltage of the LEDs used here, which amounts to 3.5 volts.
The extra 2.5 volts rise can cause considerable dissipation and loss of power through heat generation.
Therefore I employed a few diodes in series with the supply and made sure that initially when the battery is fully charged; three diodes are effectively switched so as to drop the excess 2.5 volts across the white LEDs (because each diode drop 0.6 volts across itself).
Now as the voltage of the battery drops, the diodes series are reduced to two and subsequently to one making sure only the desired amount of voltage reaches the LED bank.
In this way the proposed simple emergency lamp circuit is made highly efficient with its current consumption, and it provides backup for a much longer period of time than what it would do with ordinary connections.
Circuit Diagram
How this white LED Emergency Light Circuit Works
Referring to the circuit diagram, we see that the circuit is actually very easy to understand, let’s evaluate it with the following points:
The transformer, bridge and the capacitor forms a standard Power supply for the circuit. The circuit is basically made up of a single PNP transistor, which is used as a switch here.
We know that PNP devices are referenced to positive potentials and it acts like ground to them. So connecting a positive supply to the base of a PNP device would mean grounding of its base.
Here, as long as mains power is ON, the positive from the supply reaches the base of the transistor, keeping it switched off.
Therefore the voltage from the battery is not able to reach the LED bank, keeping it switched off. In the meantime the battery is charged by the power supply voltage and it’s charged through the system of trickle charging.
However, as soon as the mains power disrupts, the positive at the base of the transistor disappears and it gets forward biased through the 10K resistor.
The transistor switches ON, instantly illuminating the LEDs. Initially all the diodes are included in the voltage path, and are gradually bypassed one by one as the LED gets dimmer.
HAVE ANY DOUBTS? FEEL FREE TO COMMENT AND INTERACT.
Parts List
R1 = 10K,
R2 = 470 ohms
C1 = 100uF/25V,
Bridge diodes and D1, D2 = 1N4007,
D3---D5 = 1N5408,
T1 = BD140
Tr1 = 0-6V, 500mA,
LEDs = white, hi-efficiency, 5mm,
S1 = switch with three changeover contacts. Using Transformerless power supply
The design presented above can be also made using a transformerless supply as shown below:
Here we will discuss how an emergency lamp can be build without a transformer using a some LEDs and a handful of ordinary components.
The main features of the proposed automatic transformerless emergency light circuit is though very identical to the earlier designs, the elimination of the transformer makes the design pretty handy.
Because now the circuit becomes very compact, low cost and easy to build.
However, the circuit being completely and directly linked with the AC mains is hugely dangerous to touch in an uncovered position, so it is obvious that the constructor implements all the due safety measures while making it.
How it Works
Coming back to the circuit idea, transistor T1 being an PNP transistor tends to remains in switched OFF condition as long as AC mains is present across its base emitter.
Actually here the transformer is replaced by the configuration consisting of C1, R1, Z1, D1 and C2.
The above parts constitute a nice little compact transformerless power supply, capable of keeping the transistor switched OFF during mains presence and also trickle charges the associated battery.
The transistor reverts to a biased condition with the help of R2 the moment AC power fails.
The battery power now passes through T1 and lights up the connected LEDs.
The circuit shows a 9 volts battery, however a 6 volt battery may also be incorporated, but then D3 and D4 will need to be completely removed from their positions and replaced by a wire link so that the battery power is able to flow directly through the transistor and the LEDs.
Automatic Emergency Light Circuit Diagram
WARNING - THE CIRCUIT IS NOT ISOLATED FROM AC MAINS, AND THEREFORE IS EXTREMELY DANGEROUS IN POWERED, UNCOVERED POSITION.
Video Clip:
Parts List
R1 = 1M,
R2 = 10K,
R3 = 50 ohm 1/2 watt,
C1 = 1uF/400V PPC,
C2 = 470uF/25V,
D1, D2 = 1N4007,
D3, D4 = 1N5402,
Z1 = 12 V/ 1Watt,
T1 =BD140,
LEDs, White, High Efficiency, 5mm
PCB Layout for the above circuit (Track side view, Actual Size)
Pats List
R1 = 1M
R2 = 10 ohm 1 watt
R3 = 1K
R4 = 33 ohm 1 watt
D1---D5 = 1N4007
T1 = 8550
C1 = 474/400V PPC
C2 = 10uF/25V
Z1 = 4.7V
LEDs = 20ma/5mm
MOV = any standard for 220V application
For High Watt Application
Emergency Lamp with Automatic Day Night LDR Activation
In response to the suggestion of one of our avid readers, the above automatic LED emergency light circuit has been modified and improved with a second transistor stage incorporating an LDR trigger system. The stage renders the emergency light action ineffective during day time when ample ambient light is available, thus saving precious battery power by avoiding unnecessary switching of the unit.
Circuit modifications for operating 150 LEDs, requested by SATY:
Parts List for the 150 LED emergency light circuit
R1 = 220 Ohms, 1/2 watt
R2 = 100Ohms, 2 watts,
RL = All 22 Ohms, 1/4 watt,
C1 = 100uF/25V,
D1,2,3,4,6,7,8 = 1N5408,
D5 = 1N4007
T1 = AD149, TIP127, TIP2955, TIP32 or similar,
Transformer = 0-6V, 500mA
Emergency Lamp Circuit with Low Battery Cut-off
The following circuit shows how a low voltage cut off circuit can be included in the above design for preventing the battery from getting over discharged.
Power Supply Circuit with Emergency Backup
The circuit shown below was requested by one of the readers, it is a power supply circuit which trickle charges a battery when AC mains is available, and also feeds the output with the required DC power via D1.
Now, the moment AC mains fails, the battery instantly backs up and the compensates the output failure with its power via D2.
When input Mains is present, the rectified DC passes through R1 and charges the battery with the desired output current, also, D1 transfers the transformer DC to the output for keeping the load switched on simultaneously.
D2 remains reverse biased and is not able to conduct because of higher positive potential produced at the cathode of D1.
However when mains AC fails, the cathode potential of D1 becomes lower and therefore D2 starts conducting and provides the battery DC back up instantly to the load without any interruptions.
Parts List for an emergency light back up circuit
All Diodes = 1N5402 for battery up to 20 AH, 1N4007, two in parallel for 10-20 AH battery, and 1N4007 for below 10 AH.
R1 = volt/charging current (Ohms)
Transformer Current/Charging current = 1/10 * batt AH
C1 = 100uF/25
Using NPN transistors
The first circuit can be also built using NPN transistors, as shown here:
Ken says
Sir does this circuit has a protection for overcharging the battery?thanks sir
Swag says
Hi Ken, A special cut off circuit has not been included for the sake of simplicity, however R2 in the first design and R3 in the transformerless designs are used for limiting charging current to the battery ensuring that once the battery is fully charge current drops almost to zero and these resistors help to prevent the battery from getting overcharged or damaged.
Ken says
Thanks sir,another question sir,.can i use 750mA transformer instead of 500mA?,.
Swag says
Hi Ken, No problems it will do, just dimension the mentioned resistor accordingly to ensure overcharging does not happen for the battery
Ken says
Sir how many LEDs can i put in this circuits?,what is the maximum no. Of LEDs,….and i can use 750mA transformer instead of 500mA?,thanks sir
Swag says
The number of LEDs will depend on the Ah value of the battery, preferably the total LED current must not exceed 30% of the battery’s Ah rating
Ken says
Sir can i charge 6v 7Ah to a 6v 2.8Ah charger?thanks sir
Swag says
Hi Ken, yes you can charge a 7Ah battery with a charger meant for 2.8Ah battery, but the charging rate may be very slow.
अमन says
हाई सर प्लीज़ अंडरस्टैंड। मैं इंग्लिस में कमजोर हु इसीलिए हिंदी में लिख रहा हु। किया मुझे इसी सर्किट की जान कारी हिंदी भाषा मे मिल सकती है? मुझे 7वाट AC/DC बल्ब का सर्किट डायग्राम ओर कॉस्टिंग चाहिए। जैसे ( सिस्का ) या कोइ ओर कंपनी के जैसा। जिसे होल्डर में लगाने के बाद AC पे चलता रहे। ओर बैटरी भी चार्ज होती रहे। AC POWER कट होते ही बैटरी पे चले। बिना कोई और स्वीच ऑन करे। हा अगर जो होल्डर का बटन जो कि बोर्ड में लगा होता है। उसे अगर बंद कर दिया जाये तो। जो अब बैटरी पे चल रहा है बंद हो जाये। आप की वेब साइट को google translator पे translate कर के देख चुका हूं लेकिन। ग्राममर में बोहत गड़बड़ हो जाती जिसे समजना बोहत मुश्किल होता है। में उम्मीद करता हु के आप मेरे comment का जवाब जरूर दोगे। धन्यवाद।
Swag says
Hello Aman, tum doosra ya teesra wala circuit bana sakte ho. PCB design bhi diya hua hai. kuchh technical calculation karne honge, mai jaldi hi upadte kar dunga.
Total cost hoga = 50 se 80 rupay tak bina battery ke
7 watt pane ke liye 1 watt ke 7 LED parallel lagana hoga
Aman says
Thank you sir for you qiuk reply, I will wait for update.
Swag says
I have updated the diagram, see under the PCB
अमन says
Sir koi best software bataye cercuit simulation k liye with PCB 3D diagram. Jis me circuit ko run karke dekha jasake jis me total electronic part ho.
Swag says
sorry uske bare me mujhe nakhi pata.
अमन says
Or ha ye jo led circuit ka diagram he, is me battery over charge protection nahi he shayad?
Swag says
over charge protection nahi isme, lekin agar full charge level ko thoda kam rakha jaye to over charge ka khatra nahi rahega. Agar 3.7V ka battrey hai, to charge volateg ko 4V par simit rakhna hai. 7 diodes ho kam jada karke is voltage ko adjust kiya ka sakta hai
अमन says
Or ha sir agar parts ki detail mill jaye jayse capacitor , Polaris he ya non Polaris to bohat achchha hoga. Thanks in advance.
Swag says
All resistor 1/4 watt 5% except R3 which is 1 watt
C1 = 5uF/400V PPC or metallized polyester
C2 = 100uF/16V electrolytic
अमन says
Thank you very much sir for all reply
Rajkumar says
Sir,
Thank you very much for your reply
Swag says
welcome!!
Rajkumar says
Sir
My Chinese emergency light transistor was burnt so I need it instead of the other one transister. Here is the mentioned in D2470. Can you tell something in equivalent transister?
It has a 4v 4Ah battery.
Thanks in advance
Swag says
Hi Rajkumar,
you can try D1351, D880, or TIP31C
Paul says
Thanks. I have LEd rated operating current of 100-300mA and forward voltage of 5-8V, what rechargeable battery and value of components to use in a transformer less power supply please?
Swag says
you will need a 9V battery, at 3AH may be. do not use the diodes at the collector side of the transistor.
for R2 use 220 ohm 1/4 watt, and make sure to connect a 10V zener across the battery terminal
rest can be as is.
Paul says
Hi Swag. I need to power an LED with operating current of 300 mA and 8 V forward voltage to obtain an output power of 30mW. What value of components do I need with a 4.5V 200mAh rechargeable battery in a transformer less circuit? please help
Swag says
Hi Paul,
a 300mA 8V LED will require 0.3 x 8 = 2.4 watts, so it won’t run on 30mW.
also a 4.5V battery cannot be used for operating a 8V LED
Paul says
Thank you for your good help and guidance.
Paul says
Thanks. How also do you determine the best resistor to use in parallel with a dropping capacitor and also in a smoothing capacitor in a transform less power supply
Swag says
any resistor above 100K and below 1M will work…..
for capacitor you can read this article:
https://homemade-circuits.com/calculating-filter-capacitor-for/
Paul says
Hi Swag. Please guide me on how to calculate the output voltage of a droping capacitor in a transformer less power source.
Swag says
Hi Paul, output voltage will not be dropped by the capacitor in a capacitive power supply, the current will be dropped, as explained here:
https://homemade-circuits.com/calculating-capacitor-current-in/
Paul says
Thanks
Paul says
Ok. I understand now what you meant. You have given the values of the components used in your circuit, but my question is how do you calculate to get those values? please explain to me the calculation.
Swag says
the component values are actually not too critical, I have approximate values set in my mind and I use these approximations while designing circuits, for example here the base resistor can be anywhere from 1K to 10k etc, having said this, formulas are definitely there but it is not crucial to go by the formulas always, you just have to know the part specs to configure all of them together.
I am able to do it quickly due to my vast experience in this field.
Paul says
How can I send you the circuit am talking about?
Swag says
If it is from some other site then I won’t be able to suggest much, if it is from this website then you can show me the link here
Paul says
Hi Swag. In your circuits, immediately after transformer, you have a bridge for rectification and capacitor for for smoothening, other circuits have been checking, if you take one side of transformer as positive and the other negative, on the positive the circuit has a capacitor and resistor in parallel before bridge and on the negative side, there is a resistor before bridge, then the others follow after bridge. I don’t understand this. please explain to me
Swag says
Hi Paul, sorry I could not understand your question, which circuit are you referring to?
the transformer circuit does not have a bridge, it has a half wave rectifier using a single diode?
Paul says
Hi Swag, please give me your email because i am really learning a lot from your circuits
Swag says
Hi Paul, I am glad you are learning a a lot here, however the comment section is the best place to communicate and interact because other readers also get the opportunity to learn from our discussion, so please feel free to comment in this forum and learn as much as you wish 🙂
Paul says
Hi Swag. Please assist me with an LED circuit that is on when water flows and off when water stops to flow in a pipe
Swag says
Hi Paul, you can achieve it in the following way:
make a Darlington pair transistor using two BC547.
connect a 1uF/25V capacitor across its base/emitter, and connect two copper probes, one terminating from base of the transistor, and another from the positive line through a 1K resistor, these probes can be used for sensing water.
the LEd can be connected between positive supply line and collector of the BJT via a 1K resistor.
Paul says
thanks so much. You are great.
Swag says
you are welcome!!
Amey says
Hello Sir,
I am trying to built a simple emergency light having 2 individual set of 4x1W LED for 2 different rooms that are powered using a single 4V 1Ah (or 2 batteries connected in parallel) Sealed Lead acid battery. The circuit should be designed with minimum components.
circuit is always connected on mains to automatically switch to backup on power failure. also it should charge the battery when the mains is On and show an indication when battery is fully charged . Both LED and buzzer indication is required.
also the battery can be charged through a DC source(Mobile Charger or 6V ) not AC
Do you have any schematic for such design..?
and also how to calculate the backup time of this circuit…?
waiting for your reply.
thank You
Swag says
Amey, you can try any one of the concepts presented in the following article
https://homemade-circuits.com/2013/03/simple-dc-ups-circuit-for-modemrouter.html
estimating back up can be difficult, you will have to check it practically.
david pathmanaban says
Sir good evening
IAM using 3w leds but light is very dim
So what I want to do.
I want LED luminate brighter
Swagatam says
Ho David, what is your battery rating?, the battery rating must be able to support the LED power, and the transistor must be rated accordingly to handle this power….
babai says
Sir I am a fan of u.I wish i could meet u.sir i have a problem ….when I connect a 4 volt smd led strip containing 34 leds to 6 volt 5 amp rechargeable battery the aluminium strip of smd led is getting heated up.please tell me why this is happening and what should I do to overcome this heating issue.
Swagatam says
Thanks Babai, do you have resistors for the LeD in the strip??
If not make sure to connect a resistor with each LED in the strip
Shibananda Mohapatra says
Design rechargeable emergency light using 6V battery and led? pls reply to my email id on clevershiba@gmail.com please…Thank you Sir,
Anonymous says
Can u say me where can i find S1 = switch with three changeover contacts.in multisim?
Kesava Raj says
Hai sir
Few doubts in this topic ..Power Supply Circuit with Emergency Backup..
I tried this circuit working well..
Today i saw in one ic datasheet..
BACKUP power supply they are using condenser and resitor, they not mention the value…
I need the value of R & C
using for 5v and 12v
Pls explain abt this type of backup circuit and how long it will hold the backup and how to calculate the values R & C.
Swagatam says
Kesava, if the back-up is for an LED then it won't work, unless the capacitor value is huge and if it's a super-capacitor.
Possibly I'll try to discuss this topic through a new article soon
Kanta says
Hi Swa,
I may buy the bulb and open it to take a look inside. The price is cheap it is about USD 3.
I will update you once i got it.
Thanks
Kanta
Swagatam says
OK sure will do!
Kanta says
Hi Swa,
I forgot to mention that the emergency bulb can stand for about 4 hours.
Thanks
Kanta
Swagatam says
It could be having a small li-ion cell and hi efficiency LEDs
Kanta says
Hi Swa,
I saw in the shop a kind of emergency bulb which is put in the common bulb fitting and doesn't require any battery. The bulb also function as a lamp when the main power exist, but when the main power goes off, the bulb is still giving the light as an emergency light. The bulb is actually contains some leds and electronical components. Do you have the circuit for this kind of emergency bulb ?
Thanks
Kanta
Swagatam says
Hi Kanta, no LED or lamp can light up without a power source, the lamp must be having a small Li-ion kind of chargeable battery inside, nowadays batteries have become very compact and efficient and can be adjusted within small spaces.
Anonymous says
hello,
Why there is not the bridge diodes in the first circuit?
Or why there is the bridge diodes in other circuits???
thanks
Swagatam says
it's just to keep the circuit simple…you can use a bridge if you wish to…
Anonymous says
thank a lot. you are super, really. I will use AC DC adapter(1,5v – 12v)..
Question 2: Can i use NiMH 5cell battery(6v) for 6v battery. thanks
my english very bad sorry:)
thanks for your helps
Swagatam says
yes you can use it
The Rocking Time says
Sir is there anyway to illuminate 50 white LEDs using a 4.7 V li ion rechargeable battery with maximum brightness output ?
Swagatam says
50 LEDs in parallel will consume 1 amp minimum, not possible, unless the batt is 5 AH rated
Anonymous says
Hello,
I've tried the circuit(first one) but when I use 9v transformer voltage out goes up to 13 v. So shall I use 6v 500mA transformer? Assuming that the normal charging voltage for a 6V 4.5 mA battery is 6.9 to 7.2 volts, and even if I use 6 v transformer charging voltage will be above the specified voltage. Is this ok? Or any other solutions? Sorry if I'm wrong here.
Swagatam says
you are correct, you must use a 6V/500mA transformer, then rectify it using a bridge diode network and a high value filter capacitor, this will allow you to get the correct charging voltage for your 6V battery.
Anonymous says
Hi,
Can i skip the diodes and connect LEDs in such a manner directly to the battery;
2 strings of LEDs in series connected to the battery with 20 LEDs connected parallel in each string. So 40 LEDs in total. Or can you suggest the number of LEDs in each string for good backup time?
Diodes I'm planning to remove is to make the circuit even more easy.
Cheers,
Swagatam says
yes you can easily skip the diodes, but make sure the LED string forward voltage is approximately equal to the battery voltage, otherwise the LeDs could get damaged gradually overtime.
VISHNU AJITH says
Sir I would like to make an emergency light using led with 1.5hr backup rechargeable battery and to stop damage of the battery, should have a automatically charge cutting system if the battery is full
Unknown says
Sir I would like to make an emergency light using led with 1.5hr backup, and it should contain a charge cutter to stop excess charging of battery.
Swagatam says
You can try this circuit:
https://homemade-circuits.com/2015/10/smart-emergency-lamp-circuit-with.html
MovieS-PoinT says
Dear sir,
I want to make a automaric circuit for 4v 3000mah batery to charging. Max volt 4.5, and min is 3.7 to drive a emergency light of 4watt. Please help me to make it
Thanks in advance..
Regards Irfan Ahmad
Swagatam says
Dear Irfan, please search for "smart emergency light circuit", you'll get the required circuit…
javed iqbal says
Any one help me I need 105 Led -718 A remote control emergencylight with 8th battry connection and circuit
faisal khan says
Hi Swagatam dear i want the basic of electronics,how can i make the project with my own ideas which are in my mind i mean the calculation from the components ie resister transister etc.
Swagatam says
Hi Faisal, you will have to first study and grasp how transistors, resistors, capacitors work in electronics circuit then study other parameters like opamps, digital ICs etc…..once you start understanding you'll automatically be able to design your own circuits…it will take time though.
K.Rajeesh Rajeesh.K says
Sir,
Thank you for reply,
I am not able to view the circuit diagram please post the circuit.
Swagatam says
I can see the circuit clearly in the linked article, please refresh it again and check.
Swagatam says
For your fish tank, you can use the first circuit from the following article:
https://homemade-circuits.com/2013/03/simple-dc-ups-circuit-for-modemrouter.html
just replace the 14V zener diode with a 2.7V zener
the adapter may be replaced with your existing 3v ac/dc adapter
K.Rajeesh Rajeesh.K says
Sir,
Thank your very much for your reply,
1, From the circuit output is 12V socket but i need to connect the small motor to pump (2V 25mA motor) what will be the resistor in can add?
2, 2.7V zener with watts?
Swagatam says
Rajeesh, A resistor will not work, you can use a 7805 IC and then further drop the voltage to 2V by adding 4nos of 1N4007 diodes in series with the positive line and feed it to the circuit suggested above….you can eliminate the zener diode at the base of the transistor if you employ this method.
K.Rajeesh Rajeesh.K says
Sir,
Thank for your reply,
Based on your instruction please find the circuit i prepared please correct if any
https://drive.google.com/file/d/0B7CEiq23JAqGSkdxSmxqLVozcTg/view?usp=sharing
Swagatam says
That's not correct, the 7805 and the 4 series diodes should come immediately after the bridge rectifier and before the TIP122….reaming circuit on the right side of the TIP122 will be exactly as shown in my article.
and the TIP122 base should NOT be connected to ground, only with the 220 ohm resistor.
Swagatam says
…and the battery is supposed to be a 3V battery not 6V
K.Rajeesh Rajeesh.K says
Sir,
Thank for your reply and i'll follow it.
K.Rajeesh Rajeesh.K says
Hi Sir,
I am looking for a circuit, 6V 4.5AH battery charger with out of 2VDC 50mA. Please help me.
Swagatam says
Hi Rajeesh,
you can use the following circuit and adjust the pot and the Rc for acquiring the required V and I specs at the output
https://homemade-circuits.com/2012/02/how-to-make-current-controlled-12-volt.html
K.Rajeesh Rajeesh.K says
Sir,
I have seen Many circuit of your are very good.
My application is to drive the Fish tank small motor (2V 25mA) and due to frequent power failure i need power backup up to 3 hours kindly provided the circuit.
K.Rajeesh Rajeesh.K says
Sir,
I am awaiting for your reply.
Unknown says
Sir tell me how many number of led used in circuit
mani says
Sri. Majumdar,
I have a suggestion for you; please give serial numbers to your circuits, so that you indicate the sl.no. of the ckt. in your replies not say the first ckt, the second ckt. etc.
svs
Paul says
Hi. I am very happy with your circuits an explanations. My problem is, I am not understanding the part of diodes used since 3 diodes are in series and each has a voltage drop of 0.6 V so I thought all will drop 1.8 V and not 2.5 V. please explain to me here.
Also explain to me the connection of S1, how is that part connected in ideal circuit
Swag says
Hi, Im glad you liked them, yes it should be 1.8V as per the calculation, but 2.5V is the recommended value, so you can add one more diode in series to enable this drop in voltage.
S1 can be a 1 pole 4 contact rotary switch configured as per the shown wiring.
Paul says
Thank you so much. I am new in circuit design. Please guide me on how to choose the correct value of the components used in your design and also their work. please.
Swag says
I appreciate your enthusiasm, however the parts list is given in the article, you just to copy it an show it to the parts dealer, the resistors are all 1/4 watt and the rest are standard type.
the working is also already explained in the article.
Unknown says
Hi sir. For Circuit modifications for operating 150 LEDs requested by SATY, what type of swith that I should use, can I use single pole double throw or single pole single throw? And How many leds should i use?
Swagatam says
You can eliminate the switch, it's not compulsory…
the LED quantity will depend on the the battery AH
gela Valenzuel says
can i use 9v battery instead of 6v? anyways thankyou sir
Swagatam says
yes you can
SIVAKUMAR SHANMUGAM says
Hi Swagatham,
I want to replace LED's with 1W leds. How many LEDs support good brightness long time and What component will changed by me. and give idea please. I want to connect atleast 10 LEDS.
Swagatam says
Hi Sivakumar, in order to illuminate 10nos of 1 watt LEDs you will have to upgrade the transistor with a TIP127 and add a good heatsink to it.
Next, arrange 3 LEDs in series, make 3 such strings and connect these 3 strings in parallel….this final LED assembly can be then used with the circuit in the indicated position….but make sure to include a 6 ohm 1 watt resistor with each LED string
Pritam Bhowmik says
I have used the 1st ckt. Just conected bd140 via 1k base resistor and add a led as charging indicator. Bt problem is that led is kept on all the time. I nee quick solution. Is my pnp faulty?
Swagatam says
where did you connect the LED as the charging indicator
Anirudh Kundu says
Thanks a lot sir for explaining me the circuit so well. I greatly appreciate it.
Am using IN4007s diodes. I had to connect 20 of them in series to get +3v at the end of the last diode. And after the 13th diode am getting +5v.
But the problem arises when i connect any one load say 3v or 5v. The voltage of the other drops.
How should i tackle this now sir?
Any refinement needed or conponents to be added? If needed please guide me.
If needed guide me in making a new circuit. I really need it sir.( as compact as possible)
Swagatam says
Hello Anirudh, 20 diodes is not correct, you should get the specified voltages with the exact set up that's shown in my previous comment. without any load connected the meter will show incorrect reading.
Check the voltage with some kind of load connected may be a 1K resistor across the 3V output. then you'll find all the respective voltages falling in place correctly….
each diode is supposed to drop 0.6V approximately
Anirudh Kundu says
Thanks sir for replying to my query.
Sir the fact is i want to make a circuit in which i have a single battery source of 9volts and i want a common ground terminal and +5v and +3v.
I know maybe its a very lame thing am asking but i really seek your guidance. I'll be very thanful if you could help me with a simple drawing of the circuit.( a drawing with a pen on paper will suffice)
Thanks.
Regards.
Swagatam says
Hello Anirudh,
you can use a single battery with a common ground and acquire all desired outputs, please see the following diagram for understanding diode connections:
9V(+)——l>I—-l>I—-l>I—-l>I—-l>I—-l>I–5V–l>I—-l>I—-l>I—-l>I—–3V
9V(-)—————————————————————————-common ground
the +9V and the -9V are the battery terminals, l>I are the diodes, which are connected in series from the (+) of the battery
at the 6th diode connection you get the required 5V and the at the end of the 10th diode you get the required 3V….all these are with respect to the common ground or the negative of the battery
I hope now it's clear to you.
Anirudh Kundu says
Hello sir,
I greatly appreciate your help with the led circuit that i needed to make.
Now i need another guidance from you.
Am in a need of getting 5v and 3v from a 9 volt battery (the cheap 9v batteries used in toys/remotes). I need to apply the voltages to a load whose power consumption is 1.65watt (max).
I seek your help and guidance in designing the same.
Thanks.
Regards.
Swagatam says
Hello Anirudh, you can use 6 or 7 series 1N4007 diodes for getting 5V from 9V and 10 diodes for getting 3V, this is the easiest way to implement this, alternatively you can also try a buck converter for the achieving the same, which will be rather complex to build and optimize.
chinmoy1955 says
Dear Swagatam,
I came across your blog today while searching for a 12V output SMPS circuit. I really appreciate your hard work and dedication to this blog. Your articles are very well written indeed. I especially appreciate your replies to queries from readers, which is a plus point especially for beginners and novices. I am looking forward to more articles from you. I shall be following your blog closely and make suggestions from time to time if you don't have any objection. Thanks a lot.
Swagatam says
Thanks so much dear Chinmoy, You are most welcome to post your opinions and comments in my blog, it'll be a pleasure to answer them….
Anirudh Kundu says
Thanks a lot sir. i was looking for something like this only.
Few more queries, as what is the value of L1(tried figuring out with the formula, but failed).
The no. of led's to be attached is 64. And the voltage say is 7.2 volts using 6 AA rechargeable batteries.
and i'll be glad if u could link me to the pcb layout. The diagram seems to confuse me sir.( i am not into electronics)
Thanks .
Swagatam says
L1 is not critical you can begin with a 20 turn coil over a ferrite rod, and measure the voltage across, you can or increase or decrease the no. of turns in order to get higher or lower voltage at the output…the wire can be any thin magnet wire.
you can keep tweaking the number of turns until you find the LED getting the optimum brightness….more turns will generate more voltage and vice versa.
I am sorry a PCB design may not be possible at the moment, if possible i'll try to update some other time when I am free.
Anirudh Kundu says
Thanks sir, but the fact is i don't want it to be an emergency light. I want to use it as a video light.
so i want something very compact without the transformer and stuff.
i'll be glad if you could guide me directly for something thats easy. Also i want to connect at least 64 led's. And also add a dimmer.
Thanks.
Swagatam says
Anirudh, you can try the following circuit for illuminating 64 leds from a 5/7V input….. use a 47K pot in place of R2 for getting the dimming feature:
https://homemade-circuits.com/2012/09/led-emergency-light-circuit-using-boost.html
Swagatam says
OK, you can try the last circuit shown in the above article with a 5V power bank
Anirudh Kundu says
Sir, i prefer using a set of rechargeable AA batteries/5v power bank/ 7.2volts camcorder battery. And the normal white led's available
I just want the power source to be rechargeable and as portable as possible. And the light to be as bright as possible and dimmable too.
thanks
Swagatam says
Hello Anirudh,
Please let me know about the LED and the battery current rating that you intend to use.
Anirudh Kundu says
Hello sir,
I am a noob in electronics. I just wanted to light up 64 led's with a 5v or 7.2 volt battery source With a dimmer to dim led's. Can you please tell how to do it.
Thanks in advance.
stuart jones says
yet another fantastic lesson.
I woild like to install nearly this as an LED light fixture in my wife's horse barn tack room where we currently have no electricity. I'd like to hook up a battery (whatever size) to a solar panel (small for a trickle charge through out the day and be active ON when she enteres the tack room or tied to a limit switch at the door – door open = light on.
brilliant! another gold star for Swagatam Majumdar
Swagatam says
Thanks Stuart, I am glad that you are liking my circuits, if you have problems while building it just let me know, I'll guide you through the procedures!
Raj says
Hello Swagatam, can you tell me if I can run 4 10watt LED for few seconds with 6 x AA batteries? I need to make a ring flash for my camera?
Which will be better? 4-10W LEDs or those smd LED strips?
Which will give more light output?
Swagatam says
Hello Raj, that looks impossible, the AA maximum delivering capacity can be expected to be 1 amp x 1.5 x 6 = 9watts, at full thrust.
and 10 watt x 4 = 40 watts,,,,, that's nowhere near to the batteries capacity.
Raj says
Please look at this video, "https://www.youtube.com/watch?v=xsd5b9p19nM". This guy made 20 10W LEDs light up with 6 AA batteries.
Swagatam says
as I told you before, 9 watt source will NOT support 40 watts, in the video the LEDs are not even mounted on heatsinks that means those are not loaded for emitting 40 watts, may be just around 5 watts….
if you are looking for a voltage booster you can try this:
https://homemade-circuits.com/2012/09/led-emergency-light-circuit-using-boost.html
Anonymous says
dear sir
in the emergency light circuit can i replace the battery with a capacitor
if yes of which value
Swagatam says
you can use but a capacitor will not give you any backup, it will keep the LED illuminated may be just for a few seconds….
gogutu says
buna seara domnule.ce modificari trebuie aduse diagramei pentru a folosi un acumulator de 12v/100A ,si cum pot face oprirea autamata a incarcatorului cand bateria esta incarcata complet.va mutumesc,cu stima
Swagatam says
you can try the following design:
https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
john ocharive says
hi thanks for your circuits they are in did very helpful in developing me but in this circuit instead of the three pin switch can't I use a relay to get just on and off and how do I do away with the third switch pin. thank you.
Swagatam says
Hi John, the switch is for controlling brightness of the LED via the diodes as the battery voltage drops, in an efficient way. If you don't want this feature you can simple remove the switch and the diodes and connect LED positive line with the transistor via a 30 ohms 1 watt resistor
john ocharive says
hi thanks for your circuits they are in did very helpful in developing me but in this circuit instead of the three pin switch can't I use a relay to get just on and off and how do I do away with the third switch pin. thank you.
Vinay Rao says
Hi Swagatam,
I thank you for your guidance and support. I am sorry for not providing you the complete information about my requirement in my previous question. It was a mistake from my end. Well as I said I have an BPL Emergency light with dual small Mercury Tubes which is a Portable lamp with 6v 4.5ah battery. It has also got the 12v 500 ma separate adapter for charging purpose. This is being used only when there is a regular power cut in our place (Normally for 2 hrs daily). Hence we need to keep this plugged in to A/C mains. We used to charge it when the battery gets completely exhausted. We just switch it on manually when the power goes off (especially in the night).
Hence in the circuit suggested by you should be always connected to the Ac mains.
So kindly suggest a circuit with overcharge protection facility with an indication dual colored LED (Red n Green).
I would like to use the 1W power LED's (warm White) for this Lamp and I guess the maximum No of LED's I can use is 5 if I am not wrong for 6V 4.5 ah Battery.
Hope you understand my requirement. If u think I can use the same Schematic suggested by u for my previous blog by making some alteration then please suggest me the those alterations to be made. Hope u help me out in this matter.
Best regards
Vinay
Swagatam says
Hi Vinay,
I have already suggested you an appropriate design in your similar previous comments, this circuit will fulfill all your requested specifications, here is the link once again:
https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
Fredrik Friis Nielsen says
Hello good people.
This blog gave me a lot of interesting information. Especially the power supply circuit with battery backup part.
The reason for this is that I am working on a Arduino based system for monitoring and controlling heating cables at my summer place. This system will eventually be gsm controlled so I quickly can get an update on for example the temperature in the bathroom. The part that I am stuck on is that I would like to have the Arduino to have a battery backup of some sort so it can still monitor the temperature around wunerable waterpipes, and possible notify me if mains power goes out. I'm thinking of using a car battery so it can last for ages if power goes out.
What changes will I have to make to the "Power Supply Circuit with Emergency Backup" circuit to make it work with a 12V car battery and still have it trickle charge slowly?
Thank you in advance for any advice.
Sincerely
– Fredrik
Swagatam says
Thanks Fredrik,
You would require a just two diodes for implementing it.
I'll post the design in a new article and let you know soon.
Vinay Rao says
Hi Swagatam…
How r u? First of all I Thank you for your great help and valuable suggestions.
I need help in my new project hope u dont mind. I have a old BPL Emergency lamp with dual Mercury tubes and now it's not in working condition. I just want to convert that unit into LED Emergency lamp. It has got 6V 4.5 Ah Battery. I would like to try the first circuit but with battery over charge protection. I also have a dual color(Red & Green) 3mm LED which I would like to use it as indicator for charging and Battery full.
Kindly let me know the modification to do in the Circuit.
Thank you in Anticipation and have great day
Vinay Rao
Swagatam says
Thank you Vinay,
The above circuit cannot be used with an over charge cut off properly, you'll have to incorporate relays (5V) for your proposed requirement, as shown in the folowing link:
https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
the zener at the transistor emitter can be removed for a 6V battery.
For indications use LED from pin6 of the IC: one from positive to pin6 and another from pin6 to ground, both these LEds must be accompanied with individual 4k7 resistors.
john ocharive says
i love these circuits but please can you post a simple 9v rechargeable battery circuit diagram for me, I need it for my project urgently pleeeeease. this is my mail address: ochar2men@gmail.com.
Swagatam says
just connect the battery to a 12V/1amp DC source via a 220 ohm resistor, let it charge for 10 hours, you'll find it almost fully charged.
for indication you can connect an LED with a 1K series resistor parallel to the 220 ohm resistor, when this LED shuts off completely you can assume the batt to be fully charged.
John Carlo Penaso says
Hi Swagatam, is it okay for me to use a 6v 1 amp transformer in the modified circuit? and is it okay for me to only use 10 LEDs? thanks
Swagatam says
Hi John, yes you can use a 6V 1 amp transformer and also 10 LEDs, arranged as given in the above explained circuits.
শুভাগত says
Dear Swagatam,
my Class 9 son is eagerly ready to construct the 150 LED emergency circuit mentioned above. But I have not find AD149 transistor anywhere in Chandni market Kolkata. Can you kindly suggest something equivalent which is available nowadays in Kolkata ?
Regards
SUBHAGATA BANDYOPADHYAY
Swagatam says
Dear Subhagata,
you can use TIP127 instead of AD149, or any other PNP equivalent will also do.
Regards.
Arun Dev says
Sir I am planning to build a portable emergency light.
My intention is that to make the light from the emergency lamp available during power failure at night only…. So the following circuits suits best for me….
3.bp.blogspot.com/-moJh2ndZPhU/UoTi75WoLFI/AAAAAAAAFsY/k8xGQ713I8c/s1600/emergency+light+with+low+voltage+cut+off.png
Now can you help me in providing details with how to add a Higher voltage cut off for the battery so that during charging, when the battery tends to overcharge it should stop charging at a suitable voltage level..
I am also planning to place a transformerless power in place of the charging transformer to make the device very portable and can be hooked easily on the wall.. SO I AM USING A 3.35 uf capacitor in parallel with a 1 M,1/4W in the Phase line and then rectifying and bringing down the voltage to the charging voltage level using a suitable zener..
So i need your valuable suggestions on these..
i shall send a model diagram to your hitman inbox. Please check it out soon.
Swagatam says
Arun, the linked circuit could be a bit complex to set up, moreover adding another high voltage cut off stage could make it even more confusing….it's better to go for the following design:
4.bp.blogspot.com/-3cQBlkTYxV4/URJZuN2F-3I/AAAAAAAAC_w/plOCVi6ZXzo/s1600/1+to+1000+watt+LED+emergency+light+circuit.png
the day/night feature is not there, but can be easily included.
Arun Dev says
Interesting… How can i modify this circuit with trickle charging ( as shown in the Figure 5 ) using a 12 V 7Ah battery and all the LEDs replaced by two LED tubes ?? How can the switching diodes be placed as per your first design ???
Swagatam says
thanks!, R1 may be increased to satisfy a trickle charge response.
You can connect more number of diodes in series with D2 for getting the required amount of voltage at the different junctions of the diode.
Ram says
BD140 not taking load of many leds. I had to remove it and made it manually by slide switch. I want to drive 48x 5mm led but it working with more then 12 led. What went wrong. I am using 500ma 9 v transformer and 6v 4 ah battery
Swagatam says
use TIP127 in place BD140, it will surely work…..use a 50 ohm resistor with each LED and eliminate all the diodes at the collector of the transistor.
Y0f4N says
just few minute ago, post some comment about protect batt from overdischarge. and now I can found preventing the battery from getting over discharged circuit here. sure I need modified for 3.7 Volt battery
Swagatam says
it will be posted soon in the new article
sat says
what is the equivalent for AD149 ( see circuit -150 LEDs requested by SATY).
Swagatam says
TIP2955 can be used
deepti sharma says
need ur help as fast u can…….totally confused for my project……which transistor is better a common base….aur ….common emitter……..
achilles hector says
the resistor above is for what?
achilles hector says
in Power Supply Circuit with Emergency Backup
Is this correct?
1. I have 12v/7.5Ah battery that means my transformer should be .75 A and how many volts?
2.the Resistor is 12v(from battery) divided by .75 A(from transformer) =16 ohms right? or wrong?
3.diode should be 1n4007.
Swagatam says
1) a 1amp trafo will also do, volts = 14V
2) resistor for what??
3)use 1N5402 not 1n4007
sat says
Sir, What type capacitor is used PPC / others (C1 = 100uF/25V circuit for SATY for 150 LEDs)
Jinnamuru Xunte says
how many led in SERIES can I use? with 12v battery
how many hours will it take to charge the battery?
can you change the power supply of this emergency light with transformerless power supply? plssssss just requesting…i'll wait here…..
Swagatam says
You can try this circuit:
https://homemade-circuits.com/2012/07/making-automatic-emergency-lamp-using.html
backup time will depend on battery AH and no of LEDs used.
Jinnamuru Xunte says
can i use 12v battery here?
Swagatam says
yes, but include 3 LEDs in each string
Divyansh Gehlot says
Hey Sam,
I am a class 12th student, could I make this one easily for my board project and can you please tell me basically what are the steps that I should take to make this one?
I lvoe this project.
Swagatam says
Hi Divyansh,
First procure all the components and also a general purpose PCB and then correctly assemble all the components over it very carefully by soldering them together using wire links.
Do all the connections correctly as per the given diagram.
Anonymous says
Hi sir,
Please i need alternatives for :
1- 1n5408
2- BD140
Swagatam says
You can use two 1N4007 in parallel for each 1N5408, and TIP127 in place of BD140
Anonymous says
can i use BC557 instead of BD140 ?
achilles hector says
I mean for the first group of question which is #3 is: not a diode a LED. thanks a lot again SIR!!!
Swagatam says
with a 6v/500ma transformer, the battery should get charged within 8 hours of time.
you can use only two or three 1 watt leds not more than that.
use two in series without any resistor and no diodes at the transistor collector.
achilles hector says
good day sir!
a question for circuit using NPN transistor:
1. If I have 6V 4Ah battery how long will it take to charge?
2. I have a problem: my transformer generates a little heat, (but no so dangerous), after plugging the circuit for about 12 hours. Is that okay?
thanks a lot for the answer.
I need it ASAP. that is before my circuit fails… 🙂
achilles hector says
Good day Sir!
A question for the circuit: Using NPN transistor
1. Can I replace BC547 and TIP122 with a 2 TIP31C?
2. Can I omit the 4 DIODES but instead use a a SPST switch?
3. Can I use 1 watt LED accompanied by 100 ohms resistor instead of 24 5mm diodes?
Swagatam says
Good day Achilles,
Although it doesn't look a good replacement but you may try it, might just work.
If you want to use a resistor in place of diodes, yes you can do it.
For 1 watt LED you will need to calculate the resistor value correctly as per the voltage specs.
Ranju says
Hi Swagatham,
I made this circuit.. Its working properly.. Thanks to you..
I wish to incorporate a Charging LED to the first circuit.. Please suggest a way..
Regards,
Ranju
Swagatam says
Hi Ranju,
Connect low value resistor in series with D2 and connect an LED parallel to this resistor with its cathode towards the battery.
The resistor value may be calculated with the help of the following formula:
R = 3/I, where I is selected 1/10 of battery AH.
Ranju says
Thanks for the reply Swahatham..
It's perfectly done and working fine..
Please suggest a way to add an LED for full Charge indication for battery..
Anonymous says
hi swagatam..
plz tell me what changes should i make in above mantioned circuit to connect only 5 1 watt leds ??
and i have 12V 1500ma adapter and i wish to charge my 6V 4.5AH bettery with this adapter ,, what should i do??
Swagatam says
use TIP127 for the transistor, use 10 ohm, 1 watt resistor for each LED (parallel connection)
remove all the diodes, they won't be required…..
Swagatam says
…do not remove D1, D2, they are required.
Anonymous says
thanks … plz also answer my 2nd question i have 12V 1500ma adapter and i wish to charge my 6V 4.5AH bettery with this adapter ,, what should i do??
Anonymous says
IT is just a inquiry.
Can we connect a led to 2V 1400Ah hi power battery, will it glow or the excessive current will blow up the led?
Swagatam says
The LED will be OK but will be dim due to low voltage, I am assuming it to be a white LED which needs 3V minimum for optimal glow.
aimal daud khan says
sir i want to know that y u used a resister of 10k ohm in parallel in the 1st circuit
Swagatam says
For providing the required negative base biasing so that it is able to conduct when mains supply fails.
mnasim31 says
Is S1 a automatic switch? If not then how it to be used manually? Thanks.
Swagatam says
No, it's manual, initially it must be kept at the topmost point, then gradually brought to the lower points for optimizing the brightness as the LED gets dimmer.
Faisal Mateen says
Dear Swagatam
I need a LED 1watt with a minimum quantity of 9 LED's to lit up without transformer but with a battery backup system.
It should lit up the led's in the presence of Electricity 220v ac.
But when electricity goes away then also the LED lights should remain ON with a battery backup system for mimimum 2 to 3 hours or more.
Please advice me the Best circuit for this purpose.
Waiting your quick reply.
Thanks & Regards
Faisal Mateen
Swagatam says
Dear Faisal Mateen,
You can try the following circuit:
1.bp.blogspot.com/-I2zlapFq6RM/UML_NxUJy2I/AAAAAAAAB3w/27ZLDjK9C9g/s1600/simple%20modem%20UPS%20circuit.png
Use R1 = 100 ohms, 1 watt and the adapter can be a compact 12V/2amp smps
Make 2 strings of 3 LEds each with individual 6 ohm/1 watt resistors.
connect these strings in parallel to the output of the above circuit.
Swagatam says
…D1, D2 = iN5402
Anonymous says
Hi Swagatam,
I am a newbie to electronics but love to make stuff to use around my house, I have built your Power Supply Circuit with Emergency Backup with a meter length strip of 12v LED's which works very well in my shed. I would like to add a 12v PIR to the existing circuit to switch the lights on when the mains is disconnected. Please could you advise me on how to do this so I do not damage the existing circuit.
Thank you
Jon
Swagatam says
Thanks Jon,
check out the second circuit in this link:
https://homemade-circuits.com/2012/09/pir-controlled-led-driver-circuit.html
connect its supply terminals across your emergency lights transistor output and ground, it would start working as per your requirement…
Anonymous says
Hi Swagatam,
I am a newbie to electronics but am enjoying making bits to use around my house, I have built your Power Supply Circuit with Emergency Backup which works very well on some 12v LED Strip lighting in my shed. But I would like to conserve the battery by adding a 12v PIR to switch it on when the mains supply is off. Any suggestions on how I could add this to the existing circuit.
Any help would be great Thanks
Jon
PS Great Site.
Anonymous says
there must be a limit, as we cannot connect 200Ah Ups battery?
I want to know that limit and how to calculate that?
Anonymous says
Would increase in Battery Ah means More Backup time or it will damage the LEDs
if it will damage the LEDs than how much battery current we must use….
Swagatam says
you can increase the battery ah it won't damage the LED, but the voltage should not increase
Anonymous says
Hello Swagatam Da,
In The first circuit, do we need not to connect a bridge rectifier circuit after the transformer.
Tanmoy.
Swagatam says
Hi Tanmoy,
yes you may connect a bridge rectifier for better response. I connected a single diode to keep it simple.
cedar says
Sir,
I really enjoy reading your articles, your talent is that, you make everything so simple. The best best part is, unlike other Circuit designers that we see in the internet, you are always there to explain or reply a reader's problem.
The only problem is, most of the people don't get spares specially for people living in North East India.
So here is a request/suggestion, why don't you start a enterprise to sell assembled kits & electronics parts of your wonderful designs? This can be sold at a higher price than market but since you will be supplying all the parts, a hobbyist won't mind buying it from one source instead of roaming the marking searching for spares.
You can send the items through postal and courier service to any part of India, like "Electronics for you Magazine, Kits&Spares"?
I am sure, this will not bring you only profit but widely popularize your designs as your circuit will be used by many hobbyist in the country.
Yours truly,
Chuba Ao
Scientist-C
Ministry of Communications & IT
Govt of India
Mokokchung, Nagaland.
Swagatam says
Thank you very much Cedar! I appreciate your interesting suggestion.
I indeed would want to implement your suggestion, but the problem is that maintaining electronic kits in a professional manner can be difficult, and providing full range is another difficult part, next comes investment which can be a bit risky. Being a sole manager of the blog all these can be difficult to handle and therefore I haven't yet started selling anything here.
However, I am studying readers interests, if things looks conducive it would't be long for me to implement the option that you have provided.
Thanks and Regards.
your INFO_JOY MAN says
That circuit will blow all leds of some one by mistake keeps switch at wrong position
Anonymous says
hello . I would like a circuit for a wall plug nightlight that has 3 common straw hat leds ,a battery backup . i would like the leds off during daylight
Thankyou for the quick reply ,
the circuit you refer is the one with the 555 timer ?
I do not see a battery backup in that circuit ?
do i use the circuit from this thread and apply output d1,d2 to the 555 circuit ?
Swagatam says
For battery back up you may refer to the second circuit from top given in this article.
https://homemade-circuits.com/2012/08/led-emergency-light-circuit-with.html
include only one LED string, as per your requirement
Jams says
I am curious if you could substitute the LEDs with a 12 volt relay in order to use higher current lighting on a separate (or same) battery? If so, would part of the circuit need "beefing up" to drive the relay?
I am thinking of using a car or deep cycle marine battery with it's own regulated charging device and then placing LEDs all over the house in discrete locations for when the power goes out. I'll make sure everything is fused for safety.
Thanks!
Swagatam says
Yes that's quite possible without much complications, I have already discussed it in this article, please refer to it:
https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
Anonymous says
hello . I would like a circuit for a wall plug nightlight that has 3 common straw hat leds ,a battery backup . i would like the leds off during daylight .
thanks
Swagatam says
you may try the last circuit shown here:
https://homemade-circuits.com/2012/01/how-to-make-light-activated-day-night.html
Eliminate T1 and the relay section entirely, connect your leds directly across the free end of R2 and ground.
Sri Vardhan Sri Hari says
thank u very much sir sry for the late reply
Sri Vardhan Sri Hari says
sir can u make the circuit very simple cuz i am a beginner but this is for my project sir. is it possible to do it with a bc54 7 transistor if so plz post me a schematic. i want to be done with a bridge rectifier and capactitors, transistor *3(max), a transformer,etc and no diodes my friend had bought one from the shop but dint show me properly. thnx in advance
soo sry to trouble u sir
Swagatam says
Check out the last circuit shown in the above article.
remove all the 4 horizontal diodes, and the switch.
connect the switch point to battery positive.
Swagatam says
make sure you connect a 50 ohm resistor with each led
Abhishek Singh says
i have made the first circuit but when i check the charging voltage comes at emitter of transistor and negative of transformer is 10v, can the circuits run for charging 6v battery.
Swagatam says
use a transformer whose current is 1/10th that of the battery ah…. the voltage will automatically adjust after the battery is connected.
Also, you should use a 0-6V transformer
Abhishek Singh says
hi,
i have completed the circuit but in that circuit the charging voltage for the battery comes to 10v, i have used transformer whose output voltage is 0-7v and the supply to led comes to 9v what shoul i do.reply me soon
Swagatam says
I didn't understand your question…
Bibin Edmond says
Hi swagatam.. Good morning.. !
can this lm317 can control both current and voltage at the same time ? if so can u send me a circuit for that. ?
Regards,
BIBIN EDMOND
Swagatam says
Hi Bibin,
Yes it can control both, you can make the following circuit, you may remove T1, R1, and replace R2 with a link.
https://homemade-circuits.com/2012/05/make-this-voltage-stabilizer-circuit.html
Bibin Edmond says
Hi swagatam,
Thank u very much yaar… let me try that circuit… !
Regards,
Bibin Edmond
Swagatam says
Hi Bibin,
You can try a LM317 circuit, nothing can be better than that.
Anonymous says
Sir, i like your all articles here specially in led lighting because its more lifewise…Sir, im in indiefilm for the first time with low budget we are still in planning we would like to use light thats not using AC volts so its mean DC volts…Sir,do you have or can you create schematic or diagram for 12 volts DC that can lights the leds at least 150-200 watts brightness with power charger?….I hope you can help us! Thanks in advance!
Swagatam says
Hi Thanks,
You may refer this article, see how R3—R14 are arranged you will have to wire the LEDs in this way, IC1 circuit is not required, you may connect the strings directly to a 12V battery (100 ah).
You will have to use 50 to 60 such strings together.
https://homemade-circuits.com/2012/11/making-40-watt-led-emergency-tubelight.html
Anonymous says
Sir, please don't post my previous comment.. i think 50 to 60 leds all…in your circuit 12 strings and 3 leds for each string…so if i have 60 leds it will be 5 leds every string? correct me if im wrong, sir…
Parts list:
R3—-R14 = 10 Ohms, 2watt
LEDs = 1 watt, 350 mA, cool white
battery : 12V battery (100 ah)
Swagatam says
a 12v supply will hold only 3 white leds in series comfortably.
so dividing 60 by 3 gives 20…..you would have to make 20 strings of 3 leds with a 6 to 10 Ohms series resistors with each each string.
Anonymous says
Sir, thanks for fast reply again…now i understand!
but what is the total power watts consumption and total watts brightness for this 60 leds and battery hours for continues using?
and if i ever want to add more leds to increase more brightness for this circuit using 12V battery (100 ah),how many leds can i add?
Swagatam says
Multiplying the optimal current with voltage of the LEDs will provide the consumption wattage of the LEDs.
100 ah means if the battery is loaded with 100 watts, it would last for 1 hour ideally, atcually it would last only for 15 minutes.
so keep the wattage well below the 100 ah mark
Anonymous says
Im so proud of you sir! You gave me a big knowledge about this circuit..
If ever i convert this 12 volts DC to AC 12 volts adapter is (for the future purposes if we have a lot of budget in our indiefilm production) is it ok?
what parts need to change or adding components in this circuits? and how many leds can i adds? or any suggestions sir if ever i can use AC volts…
I hope you can help me again sir! thanks in advance!
Swagatam says
Thansk!
As long as the power is a 12V DC, you don't have to change anything in the circuit, just make sure the adapter current is sufficiently rated for driving the connected LEDs brightly….
Anonymous says
Thanks sir! I learned a lot from you!
Swagatam says
…pleasure!
Abhishek Singh says
for more back up time of light can i replace the battery 6v,4.5ah by 6v,14ah or increase the quantity of led connected
Swagatam says
increase batt AH
Anonymous says
Sir,i want to know what is the total watts of brightness of 150 led?
Swagatam says
around 15 watts.
Subhankar Das says
sir,
i want to know that how to attache cfl lamp replacing led. please reply me.
Swagatam says
I haven't tried it yet, so presently I cannot say about the procedures…
Ram says
Hi Sir, I finally mode the 1st circuit and it also work good with 6v 5 w solar panel(used 6v, 4ah battery). Can I safely use the solar panel and set it permanent on my roof. I only tested for 15-20 minutes not continues hours. D1 already there so not added any extra diode for blocking. However autocut needs more light to switch led off. But its ok if remain on up to morning 8am.
And what will be total AH of Battery if I use 4 X 1.2v 2500mah AA battery in series to make it 6v.
When I will go to my home town I will set this to roof so i light in night and light also bright your name for all your help.
Swagatam says
Hi Sir,
You cannot connect the circuit permanently with the solar panel, because the solar panel voltage will vary with sunlight which may not be suitable for the circuit and also for the battery….and the circuit does not include an auto cut off stage so that's another issue.
dgpride says
What is purpose of the diodes in series and the selector switch
Swagatam says
for limiting the battery voltage to 3.3V without dissipating any heat and increasing the efficiency of the system.
Bibin Edmond says
Hi swagatam,
why there is no bridge rectifier on the first circuit…? and can we use IN4007 instead of 1N5408 for D3—D6 ?
Bibin Edmond
Swagatam says
Hi Bibin,
A 9V transformer has been selected for TR1, a bridge would enhance the voltage to 12V which wouldn't be appropriate for the battery, therefore only a single diode rectifier is used to make the output inefficient and lower.
In4007 will be lower in current so not suitable for the application.
Bibin Edmond says
oh… ok thanks bro… !
Bibin Edmond says
swagatam,
can we use 6a4 ( 6amp diodes) instead of 1N5408 ?
Swagatam says
yes can be used, but it will look quite bulky….
Sri Vardhan Sri Hari says
sir can u plzz make the first circuit with and npn transistor? plz plz can u make it fast becuz i have my porject coming up. and can u simplify it with a bridge rectifier plz
Swagatam says
I'll do it soon….
Swagatam says
it's posted, please check it.
imron says
Just to confirm the T1. I'm using TIP42 in place of AD149 as you suggested.
Swagatam says
yes TIP42 will do….
keeping the printed side facing you (pins downward), the right end pin is the emitter, the left pin is the base, the center is the collector.
imron says
What I mean is the circuit no. 3, the one requested by Saty. But I used only 24 LEDs. What do you recommend me to fix it? Thanks for quick reply.
Swagatam says
It's one and the same, when mains is on, the voltage from the bridge will hit the base of the transistor directly, and this will keep the transistor switched off at any cost.
anyway, you may increase the value of the base resistor to 1k or more and check the results.
Number of leds will not make any difference in the functioning of the circuit.
saty says
Hi Swagatam,
I want to thank you for the circuit which you have provided to me (3rd circuit) it is working fine.
This is saty here after long time, i thing u remember, according to the 3rd circuit for 150 LED with same setup i have built it.
1. want overload protect to the battery, since it is conneted to the mains always (470 ohms should be connected series to the D2, pls let me know is that right)
2. can i use 12v 7AH battery, if so please advice what are the components to changed or represent with clear diagram so that i can try to use the 12v battery with 3rd circuit so that i can have long backup hrs if absence of mains. Thanks in advance
Swagatam says
Hi Saty,
The above circuits are not so advanced, and does not have proper protections, if you would like to have a perfect emergency light circuit then I would suggest you to make the following design:
https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
imron says
I've successfully made the circuit with 150 LEDs, but I used only 24 8mm straw-hat typed LEDs and I found a problem with the result. The LEDs are still glowing even it's connected to the mains. I checked the output voltage to the LED (mains supply is present) and it gave 0.6 vdc. Could you tell me what's wrong with the circuit and how I can solve that kind of problem. Thanks….
Swagatam says
That's quite impossible, if the positive from D1 is connected to the base of the transistor, the transistor would never conduct.
please check your transistor, either it's blown-of or connected wrongly or may be its not a PNP transistor.
Mahendra Singh says
Hi Swagatam Majumdar. This is mahendra singh. B.Tech. in Electronics and communication Engineering in 2007. Right now i am working in a telecom company but i want to switch in Electronic Circuit designing so please suggest me is it possible and how?
Awaiting for your response.
Swagatam says
Hi Mahendra,
You may switch to electronic circuit designing field but it will require a lot of hard work to master the subject, the results will depend will depend on your level of interest and patience.
imron says
I can't find AD149 in my town. Can I replace it with 2N3055?
Swagatam says
No, you cannot…. AD149 is PNP, 2N3055 is NPN.
Try TIP42
Anonymous says
Good morning Mr. Swagatan,
Sir can you pls. tell me if i want to used a 12v car batt, what components will change? Thank you.
Swagatam says
Good morning,
with a 12V supply, there should be at least two LEDs in series on each string with individual 100 ohms resistors.
Anonymous says
Good Morning,
Thanks you very much for the reply, so the only the resistors will change, and the rest will be the same? Thank you.
Anonymous says
Goodevening Mr. Swagatan sir.
ahhmm i would just like to ask if the voltage input at the very first circuit design is DC? sorry for the nood question, I am just wondering
thank you
Swagatam says
Are you referring to "mains input" in the diagram? it's taken from the AC mains outlet…220V or 120V AC
Ram says
Can anyone from Delhi help me to find shop for buy these electronics chips. I tried to find in Lajpat Nagar Marker and Gaffar Marker but no one telling about specific shop. Its looks stupid but I can;t find a single shop to buy even a LED since years. I usually telling my brother to buy and ship to delhi. (from Darbhnaga, Bihar)
Regards
Swagatam says
Please always comment at the end of the page, it becomes very difficult to find the comment if it's posted at some other place.
It won't be possible to replace the switch of a ready made emergency light with an LDR.
You will have to make a relay type of switching circuit for doing that which can be be very complex.
Ram says
I cant figure out how to use 2nd circuit of ldr with already owned 6b emergency light to replace manual on off switch to automatically off in day
Swagatam says
I use corel-draw to draw these diagrams.
Anonymous says
sir can u just tell me how u make these circiut diagram(means u use any software or like wise) pls sir help me i have to make a electrical circuit diagram which raw drawing is with me how can i draw it with any way
muanthang says
Hi swagatham,when i connect power from transfomer to the base of (TC BD140 B7CW) transistor n from base to led.the led illuminate.is the transistor npn.pls help
Swagatam says
Hi muanthang,
The transistor is PNP…..but I did not understand your question properly….."from base to LED" meaning???
jithin says
can i use bc 548 instead of bd 140
Swagatam says
no, you will have to use BD140 or 2n2907 or similar
muanthang says
Hi swagatam,thank you four ur post.i had connected the circuit as the diagram but the led in illuminate when the power is on,and off pls help.its my mini project i need to submit this month.
Swagatam says
Hi Muanthang,
You might have connected the transistor wrongly, because if the transistor is connected as shown in the diagram it will never conduct in the presence of power supply from transformer and the LEDs will stay shut OFF when mains is present.
Please check the connections, or replace the transistor with a new one.
Ranju says
Thanks Swagatham.
Purpose of 100K Pot is to control luminosity. is n't it?
Swagatam says
Hi Ranju,
It's there to select the ambient light cut off point.
Ranju says
Hi, Swagatham,
Doubt about Circuit(2) with LDR.
1.Is it necessary to add 100K pot &1K to LDR? If necessary why is it?
2.Can i use 2N3904 instead of BC557?
Swagatam says
Hi Ranju,
You can remove them if you want, they are not critical.
3904 is NPN so cannot be used here.
NAZUGATZ says
hi Mr.swagatham i have just seen your blog while searching solar equipments, actually i like to manufacture low cost solar products if u r interested / u know any person having same idea please mail me nazugatz@gmail.com
Swagatam says
Hi Nazugatz,
Thanks for contacting me!
I am interested if it's a long term work, and if the transactions are within India.
My email is hitman2008@live.in
Anonymous says
Thanks Mr. Swagatam 🙂
Anonymous says
Thanks for your quick reply 🙂
It is electronics. We have to find a circuit which contain at least 3 IC on its circuit. It doesnt matter whether the circuit is complex or simple. But of course i'm looking for a simple one. 😀
btw, I am beginner.
Thanks for your concern Mr. Swagatam
Swagatam says
OK…. please check the below given circuit, i hope this will do?
circuitdiagram.net/wp-content/uploads/2012/09/simple-trafic-light-controller-circuit.jpg
Anonymous says
Hi 🙂
Do you have a mini project that use 3 ICs on its circuit?
Thanks.
Swagatam says
Hi,
Can you specify the project subject?
N.Muthu Krishnan says
Hi,
i like to make one ultra high bright led emergency light. fully automatic circuit diagram,with battery low cut off and battery full cut off and over load cut off and i like to use solar panel also pls give me a detailed circuit diagram pls pls…
Thank you
N.Muthukrishnan
krishna198023@gmail.com
Swagatam says
Hi,
The below given link will hopefully provide you with the required design
https://homemade-circuits.com/2012/08/led-emergency-light-circuit-with.html
masterfiles says
Thanks Swagatam for taking the pain to answer my questions even when they seem the answer is so bvious. However, the truth is that am actually asking for the working principle of the circuit. In other words, i need the 'electronics' of the circuit. Thanks
Swagatam says
Hi Masterfiles,
I have updated the diagram with the required explanation, you can check it just above the last diagram.
masterfiles says
Thanks Swagatam. That was what i wanted so i can compare with my own explanations. I really appreciate. Keep up the good work
Swagatam says
My pleasure…
masterfiles says
Good day swagatam. Please the circuit i need you to explain further is that of the "power supply circuit which trickle charges a battery when AC mains is available, and also feeds the output with the required DC power" I want to see if your explanation of the circuit's workings will match what i have in my head.
Swagatam says
Hi Masterfiles,
Please check the last circuit diagram, it's exactly what you are looking for….
masterfiles says
Hi swagatam. Thanks for your prompt response and am writing to acknowledge that the red LED is now indicating as expected. Please kindly share more knowledge with me about the working of the power supply circuit with emergency backup. Thanks once more as i expect your usual prompt response.
Swagatam says
Hi Masterfiles,
I have explained the power supply working in the article, you can find the entire explanation just below the first diagram.
Regards.
masterfiles says
Hi Swagatam. Am building this circuit correctly for the second time. In my last construction, i added a red Led in series with a 1k resistor after the capacitor for AC on indication. However, the red LED lights even when battery is used and no AC. I suspected diode D2 and tested it only to find it is ok. I therefore believe there is leakage current problem which dissipates power even when battery is not in use. Please i want your view and suggestions on this. Thank you.
Swagatam says
Hi Masterfiles,
Connect the LED/1K series directly across the transformer secondary winding. This will give the correct required indications and will keep the LED switched OFF in the absence of AC power..
Anonymous says
Hi, Swagatam,
I appreciate your generosity of posting your innovative ideas in electronics. I was looking your schematic diagram of LED emergency light circuit. I guess LEDs will light when AC power is used.
If we would see it on the principles of biasing transistor. Am I right?
Is the switching on of transistor does not affect the current flow to LEDs when battery supply is used?
Swagatam says
Hi friend, thanks!
The transistor used is not an NPN, rather a PNP, that means a positive biasing will keep the transistor switched OFF.
Thus, in the presence of AC mains the LEDs remain switched OFF, and illuminate the moment AC fails.
I hope you got it.
Regards.
Anonymous says
hi sir,
i am kiran.i had lot of difficulty in giving numbering to ic.can you say how give numbering to an ic
Swagatam says
Hi Kiran,
Hold the printed side of the IC toward you, then the pin at the left of the slot or the half-notch on the IC, is the pin#1 and the pin which lies at the right of the given notch, is the last pin of the IC, I hope you got it.
Regards.
pp says
Hello Swagatam..
Part list for Power Supply Circuit with Emergency Backup is NOT published???
what are values of D1..D4, D1, D2, R1 and C1 and also about the transformer..??
Does it protect Batt. form over-charging.
Regards,
Swagatam says
Hi PP,
Now it's published, thanks!
If the resistor is chosen for trickle charging then it might not damage the battery, but at higher currents this circuit will not protect the battery from over charging.
Regards.
M&D says
Hey Swagatam,
Nice to find you here. I have come to you with a query.
I have designed a LED lamp operating on 230 v ac, using a X capacitor to drop the voltage and driving 4 strings of 35 white LED's = 140 LED's. The circuit is working well and I am aware that the circuit is not isolated.
What I would like to know, is how exactly is why the X capacitor makes a humming noise? What parameters should I keep in mind, when opeating at low temperatures?
Thanks for the help.
Madhav
madhavdivya@gmail.com
Swagatam says
Hi Madhav,
Thanks! Welcome to my blog.
If the capacitor is making noise, means it's not a good one, replace it with a correctly rated, good quality capacitor, for example you may replace it with a 105/400V PPC capacitor.
Low temperatures won't affect the circuit in any way, because the parts used are not critical and has wide temperature tolerances.
Regards.
kdude says
Hi Swagatam
I am trying to build an always ON LED light.
It will work from an AC to DC adapter (3.3V) during normal operation.
I want to connect a 3V battery along with LED in parallel to this adapter.
Will this work?
Please help!
sandy says
hi
can u give the specification of capacitors and resistor o be used for 12v transformer input?
and specif the diodes?
sandy says
sorry …i am asking about the battery backup circut when main power fails….what is the transformer ,resistor,capacitance specification should be used for 12 volts battery….and is it posible to stop battery charging when battery is complectly filed,with zener diode?
Anonymous says
1. What type of battery is being used? Lead acid, gel, etc.?
2. I thought that when led are placed in parallel, one may hog the current due to variation in characteristics of the leds, and therefore a resistor is normally used to limit the current…?
3. Would the series diodes (not leds) consume as much power as resistors?
4. You mentioned that ideally a constant voltage source is being used here. Aren't constant current sources better drivers for leds?
Regards,
Donovan
swagatam dash says
pls give a ckt diagram of IR light use in CCTV night cameras .
datta says
hi what is mean by switch with three change over contacts.
Anonymous says
How many hours the LED glows after AC switched off……?
Anonymous says
Hi Swagatam…. 🙂
thanks…
i am doing 2nd circuit above…. that is With LDR…. i can put 45 to 50 LED's for 6v 4ah battery….? and how many hours it will glow….?
Swagatam says
OK you may do it, but please note that I haven't tested it practically, though I believe that it should work as expected.
Yes you may connect 50 LEDs, just connect a 10 Ohm 1/4watt resistor with each LED for better uniformity of light.
According to me it should stay ON for around an hour
Anonymous says
Thank u…
Which circuit u did practically and working good….?
for 30LED's what is the backup time, for 6v 4ah battery.
Swagatam says
I tested the above circuits without the LDR, and with less number of LEDs.
For 30 LEDs back up time will be around 1 and 1/2 hours or so.
Anonymous says
ok thanks…. 🙂
Anonymous says
Hi,
how much back up time (approximate)will be there from the 150 led circuit?
Anonymous says
4.5 Ah battery
Anonymous says
For the circuit with 24 LED's how many more LED's can i add without losing too much back up time from the battery.Battery 6v 4.5 Ah? Please help!!!
Abhishek Singh says
can i increase ah capacity of battery or quantity of led.
ex- can i take 6v,14ah battery from market instead of 6v,4.5ah for more back up. reply me soon.
Swagatam says
yes you can do it.
Abhishek Singh says
i am making the first circuit in that 24 leds are used so if i use 6v,14ah battery then there is harm to led or not.reply me soon ( i am using eon rechargeable battery it is good or not).
Anonymous says
can i use 4.5 v 300 mA(output is around 6-7 volts) transformer ??
arun says
sir ,can i get a transformer less emergency which charges battery when there is supply and lights when power fails.the circuit also should cutoff when battery is fully charged
Anonymous says
Hi,
For the last circuit(Emergency Backup)can i connect LED's as in the 1st circuit(with 12 LED's)?And the diodes used (D1–D4 , D1,D2)is IN 5408?
Anonymous says
hi,
i can add a switch for the LED's right?What about the diode value?
Anonymous says
Thank u for the reply
Anonymous says
Hi,
I completed the circuit,connected to the mains(via 0-9v 500mA tranformer),measured the output at battery out(without battery,led's) and i got 13.xx volts.Is it high?? or when i connect to the battery,it will run fine?Please help
Anonymous says
Can i use some high watt resistor in series instead of diodes?If yes what will be the value and where to connect it?I used 9v transformer as it is given in the list.Please help!!!
Anonymous says
Hi,
I have BD 140 transistor and i dont know is it PNP or NPN.Is that ok?Sorry for the noob question:)
Anonymous says
Thank u for the reply
Anonymous says
You can Check for its pins, using a multimeter, Just type in Google About finding the pins of the transistor,I have also done the same thing. BD140 is a PNP transistor.
Tanmoy
Anonymous says
can this circuit will be able to provide the same brightness as normal incandescent emergency lamp?
Anonymous says
Not sure. Do you mean peak current when the motor is being driven during the resin re-charge cycle or whilst in dormant mode when just the PCB with water flow-rate detection and clock is running?
Rahul says
Hi…. actually i am an MBA by profession, but i have great interest in Electronic projects and i always make different different projects.
So after seeing this project i got an idea to do a project with 5 piranha high flux LED, which would be powered from 230volt AC main, but i am getting the circuit diagram, if anybody can help me out in having the complete diagram…please
Mohammad Saif says
Hey plz show me diagram of charging that look simple its too hard diagram
Anonymous says
Absolutely correct. The transformer output is rated at 12V 120mA.
(Sorry for not getting back to you sooner.)
Anonymous says
It would be good to have an adapter module built that includes the battery and electronics that simply inserts into the existing DC plug and socket so should I need to remove it, the original transformer and PCB device is unaffected, no wires are spliced, and they can be reconnected without any fuss…
Thanks!
Anonymous says
If it's a few milliseconds it might just work!
The application is indeed a strange one. Living in hard water area, we have a water softener unit that has a controller PCB connected to the mains via a plugin transformer. Unfortunately my village suffers from frequent outages when it rains or when the wind blows. Seriously. As soon as the power returns, the softener, by design, recharges the resin with salt which incurs some expense. It doesn't have the ability to keep track of recharges between power outages. That means if we have a pretty bad day, the entire vessel of salt can be emptied without ever drawing softened water from the taps. Hope the application make sense!
Anonymous says
Hi,
I'd like to use your design to prevent a device connected via a transformer to the mains going through a startup cycle every time a power outage occurs and power returns. Do you have any idea of the delay between the mains power failng and the power being provided by the battery? Perhaps this circuit would not work for me if the period is long enough for the device's board to sense a momentary drop in voltage and treat that as an outage.
Also, how would the circuit change if I built an adapter circuit that fitted between my existing transformer output plug, and the device's transformer input socket? I apologize in advance if I'm not providing enough information for you to answer that. I guess the off-the-shelf AC to DC transformer unit will have some components built into in on the DC side.
'Much appreciated,
Arif
Anonymous says
Hi! I'm planning to build this project. May I know if this ckt. will not overcharge the battery if left connected permanently on AC? As this will be use for emergency cases only when power outtage occurs.
Anonymous says
Can you add an LDR also, so that during daylight when mains supply is lost the LEDs don't light up and waste energy.
Bob says
I am never comfortable with transistors and can never seem to work out which pin/leg is which and which way round it goes. Is there an easy way to tell? – is it measurable with a multimeter?
Vivek says
hi swagatam i want to make use of my computer ups as a emergency LED light. so really need ur help for the things i required n what is the circuit diagram for that n all. plz suggest