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Smart Emergency Lamp Circuit with Maximum Features

Smart Emergency Lamp Circuit with Maximum Features

In this post we learn about a simple yet sophisticated automatic emergency light circuit which can be considered "smart" due to the involved advanced features and an inexpensive design. The idea was requested by Mr. Lokesh.

Technical Specifications

Hi sir, I am so glad to see your interest towards electronic circuits. So eagerly waiting for circuit which will be having following (few or all) feature.

- Low Battery Cut-off
- Overloading protection
- Short Circuit protection
- Reverse current protection
- Reverse polarity protection
- Thunder protection
- Over discharge protection
- Auto battery shut-off at Low voltage detection
- Overcharge protection
- Auto charge stop/ High Volt Detection
- Battery capacity level display(SOC)

Making this circuit for underprivileged location as donation for poor via charity So hope I can have one ckt diagram with some or all features mentioned above or lts link..

Looking for your reply ..
With full excitement

Thank you

If successful I am in plan to put ur & website name on my device ๐Ÿ™‚
As part of tribute to you sir

The Design

Amongst the many interesting features requested above only two are not included in the proposed smart LED emergency light circuit which are: 1) Battery Capacity level indicator, and 2) thunder protection.

The battery capacity level indicator is eliminated to keep things simple in the design, and the thunder protector feature is not considered in the circuit since it may be included in the form of an external attachment and cannot be a part of the electronic circuit.

Apart from the above all the remaining features are included in the design making it a truly impressive and a smart.

Let's understand the simple yet advanced design in detail with the help of the following description:

many feature emergency lamp smart circuit

Referring to the above shown smart automatic emergency light circuit, the IC 741 forms the battery level detector and the cut off stage.

How it Works

The 10k preset is adjusted such that the output of the IC goes just positive whenever the "full battery" is reached at the selected level

This is indicated by the illumination of the green LED and the shutting off of the red LED. When this is detected the IC goes into a latching mode due to the presence of the 100k feedback resistor.

Since this 100k resistor also forms the hysteresis control and becomes responsible of restoring the charging process at the desired low battery level, it must be so selected that it executes this low charge restoration process at the correct preferred low battery level.

During the absence of mains power, when the low level is detected by the opamp, the TIP122 is instantly switched OFF to prevent over discharging of the battery.

The transistor TIP122 becomes the LED driver device, which triggers ON into a standby mode as soon as the battery gets fully charged, and switches ON the LED in case the mains power fails.

Calculating the Current Limiter

The associated BC547 transistor ensures a safe, restricted current to the LED as set by the value of the resistor Rx.

Rx is calculated with the help of the following formula:

Rx = 1.2 / LED max safe current (in amps)

The PNP transistor on top is positioned to supply the charging voltage for the battery. It is enabled in the switch ON position whenever the battery voltage is detected to be below the lower threshold and while the opamp output is rendered negative or low, on the other hand this PNP transistor is instantly switched OFF when the battery is detected to be fully charged and the opamp output toggled to a high or a positive potential.

The supply voltage at the collector of this transistor may be derived from any standard SMPS AC/DC adapter unit.

The feed back link from the collector of the PNP transistor to the base of the BC547 takes care of the emergency LED changeover action, which ensures an immediate, automatic switch ON of the LED whenever the grid voltage fails and vice versa.

If you have any further questions regarding the design, you may feel free to use the comment box below to jot in your valuable feed backs.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

97 thoughts on “Smart Emergency Lamp Circuit with Maximum Features”

  1. Hello. I did your circuit and I’m planning to use 12.6v lithium ion battery. I tried the circuit with 15v adapter and 12v 5watts LED bulb. The bulb lightened up but it is so dim. I want to have a brighter output for the bulb. What can you suggest me to do?

    Thank you very much! This project will determine my final grade.

    • Hello, the brightness will depend on the battery current and voltage. If battery power is low led brightness will be low. And while the adapter is connected the LED will remain shut off. Please note that the circuit should be implemented by understanding the stages correctly, otherwise you may find it difficult completing it. If You have further problems, please free free to ask me.

      In the meantime please try reducing the base resistor of TIP122 to 1K, and see if that helps, and make sure the green LED is ON when the adapter is not linked with the circuit.

        • I am glad you understood how it works! A switch can be added in series with the battery positive wire. For the adapter, you can put it in series with the positive wire of the adapter.

  2. I want to use charger socket for my DC adapter. But I don’t know where to connect the positive, negative and ground? Can I have some help please?

    Also, do I need to change anything if I am going to use 12v adapter and 8.4 li-ion battery?


    • you can cut the socket, and look for red and black wires from the adapter cable. then you can use a 7809 IC for dropping the 12V from these red/black wires to 9V. Finally this 9V could be used for charging your battery. But make sure to adjust the opamp to cut off at 8.4V otherwise the battery may get damaged.

  3. 1.What will be the adapter that I need to use if I will use 12v lead acid battery that are commonly use in motorcycles?

    2. Do I need to change some components?

    Sorry for the trouble. Thank you.

    • for a 12V battery, you can use a 14V adapter, with current rating 8 t 10 times less than the batter Ah rating, this can be achieved simply by using a 0-12V transformer and rectifying it with a bridge rectifier and filtering using a 2200uF/25V capacitor.

      no changes would be required in the circuit, just remove the 100k resistor, it is not required

  4. Hi again! What about the DC voltage for main adapter? If I will use 12v, 15 ah lithium ion battery?
    Thank you! Your reply will be really appreciated.

  5. Hi! If I will follow the whole circuit with 5 watts LED bulb and 12v as the main supply, what kind and value of battery can I use? I’m not really good at this. Hope you understand. Thank you so much.

  6. Hi, Am going to make a emergency light circuit with 4v, 3A battery (4v battery*3 Nos in parallel). Can I use the above same circuit or do I require any changes in the circuit with 6A4 diode and 4V7 Zener?

    And regarding the regarding the LED current limiting calculation,
    Rx = 1.2 / LED max safe current (in amps)
    If I use 5mm LED means, the current will be 20mA (I.e. 0.02A).
    So the calculation will be as 1.2/0.02= 60ohms.

    If 10 LEDs means, 1.2/0.2= 6 ohms. Am I correct?

    • Hi, you can use the same circuit for any LED and battery specs only by replacing the current handling diode and the transistor.

      In your case you can use a 2N2222 or 8050 transistor instead of TIP122, and use a 1N4007 diode in place of 6A4

  7. Hi Swagatam,

    I plan to use 12 volt 7 Ah lead acid battery and 10 watt led for the project.

    1. What is the value for RX resistor should I use?
    2. Can I use 12 volt 1 Amp dc power supply adapter for the main power input?
    3. How to add an ‘LDR’ to the circuit and what type of LDR should I use?
    4. Is there any other electronic components to be added apart from those mentioned above?

    Thank you so much for your help.

    • Hi Kenny, here are the answers:

      1) Rx = 1.2 / LED max safe current (in amps)….. assuming your LED voltage rating is 12V, it’s safe current would be 10/12 = 0.833
      Therefore Rx = 1.2 / 0.8 = 1.5 Ohms, 2 watt

      2) 12V will not charge a 12V battery, you can procure a 0-12V transformer, rectify its output using a bridge erctifier and a 2200uF/25V capacitor and use the resulting output for the charging supply.

      3) You can connect an LDR across the base of BC547 and the positive line, and also make sure to add a 47K resistor across base and emitter of the BC547.

      The green LED should be removed from the shown position and put at the base of TIP122 in series with its base 10K resistor.

      That’s all no more changes would be required.

  8. hi Swagatam
    I constructed the circuit I can determine the low level indicator but the full charge led is not working. I don’t know my mistake.

    • Hi Abba, remove the green led from the shown position and connect it in series with the transistor base resistor, make sure to adjust the full charge cut off by first disconnecting the 100K feedback resistor

  9. hi Swagatam
    nice circuit nice explanation. can we use resistors as in voltage divider as Vref instead of Zener diode in the comparator input?
    thanks in advance

    • Thanks abba, a zener guarantees a perfect fixed reference which a resistive divider cannot, therefore a zener clamp is recommended here.

  10. Hi Swag,

    Your site is a gold mine! Thank you very much. I haven’t tried to build any of your circuits yet, but I did an electronics course without practicals. Your detail in explaining the components and their characteristics makes everything very clear. This will help me endlessly to sharpen up my knowldege and skills.

    Again, thank you very much for all the time you spend in doing all this work.

  11. Hi dear Swagatham,
    I have assembled almost 75% of this circuit. Now I stopped due to lack of few components in my hand. But will finish soon. OP amp section finished, working perfectly.

    1) Eg:- For charging 8.4v battery (2×4.2v li-ion in series) .
    When the battery voltage is below 8.4v, the opamp output will be low, thus TIP122 base also will be low. Circuit will charge battery, shut off TIP122, because opamp output is low.
    When battery is fully charged (say 8.4v),consider mains supply OFF, LED will switched ON.
    After few minutes, depending upon LED current, battery voltage will go down 8.4v, opamp output will suddently become low. That way shutdown LED. Am I correct….?
    I want to lightup LED inbetween 5v to 8.4v range, when mains is not available. How can I solve this issue.

    2)What is the function of 0.22mfd disc capacitor in this circuit….?

    3) Zener diode current limiting resisor you have used here is 1k, but in some other circuits, it is 10k. Which one is most suitable value….?


    • Hi Anil,
      It is not recommended to discharge a 8.4V battery to 5V it will damage the battery gradually and reduce its life drastically. 7V is the last limit.

      However, the opamp’s lower threshold restoration can be pulled down to 5V by adjusting the 100K feedback resistor appropriately, if required.

      0.22uF was introduced to ensure that the opamp resets to its initial state and forces the recharging of the battery whenever mains power returns, regardless of the charge level on the battery….however a closer inspection reveals that the 0.22uF will not actually accomplish this, I’ll try to solve it through some other means and update soon.

      zener diode resistor can be 1K for upto 12V supplies above that 10K is recommended.

      • Thanks dear Swagatham for clearing my doubts.
        One more doubt I have, You mean the hysteris control will serve the purpose of a battery deep discharge protection function…..?

        For all enthusiastic readers and you, I wish to share the following….
        I finished the battery charging section with full charge cut off part succesfully…….!!!!

        I avoided the constant current led driver section and automatic LED switch OFF section when mains is available , because I just want to use the circuit as a battery charger module with battery full cut off and restore function ( hysterisis control ) only. (Actually, not yet tried the hysterisis section, but will try soon.)

        (NB: instead of LM741, I used 1/2 op-amp of LM358. Remember, LM741 and LM358 are not pin to pin compatible.
        I did not used 3v zener diode at ic output pin, but my circuit is working well without this zener.)


        • You are welcome Anil,

          The hysteresis in opamps is simply to ensure that the opamp does not switch its output ON/OFF rapidly at the input differential thresholds rather implements it with a delayed effect, this delay is introduced via the hysteresis resistor.

          you can learn more about it though this example concept


          the 3V zener helps to ensure that if the opamp has any offset leakage voltage at its output it is blocked by this zener, so this zener is ideally recommended to facilitate a failproof operation of the circuit.

          anyway, congrats on your success, and keep up the good work

  12. Hi Swa,
    I just got the time to the project again. I did what you have told me, by connecting a series diode 1N4148 (cathode to pin 3) and preset 100K to anode of the zener at pin 6. When i do the trimming, there is no effect. I am wondering should i reverse the lead of the diode (anode to the pin 3).

    • Hi Kanta, the voltage has to go from pin#6 to pin#3 so your diode cannot be reversed otherwise it will yield nothing…..you will be able to do it successfully only once you have understood the working properly….the 100k preset value must be set such that pin#3 just reaches below pin#2 voltage when the battery voltage drops to its lower discharge threshold (and this needs to be done after pin#6 has become high)…alternatively you can refer to the following idea and try to implement this in your circuit


  13. Hi Swa,
    What i meant i have constructed the system in the PCB, however for setting the cut off and over discharge protection correctly we need to do it with the variable PSU to do the setting on high and low threshold. So, when i lower down the PSU to 6.9V, the TIP 122 became off. This is what i meant. Please help me how to set it to have the threshold to 5.5V.

    As for the main DC minus (-) connetion to pin#4, i am referring to your answer to one of the readers in the above comments. So, what is the correct way to connect the minus main DC minus (-), to battery minus (-) or to pin #4 of the IC ?

    • OK, first I would suggets you to connect two LEDs with series 1k resistor across the pin6 and the (+)(-) rails, I am sure you know how to do it.

      initially keep the 100k disconnected and now set the 10k preset for the full-charge threshold cut off…this should illuminate the lower LED and shut off the upper LED….and also the 2N2907 or the 8550…and swtch ON the TIP122.

      seal the preset now with any glue.

      now replace the 100k feedback resistor with a 100K preset, connect it across pin6 and pin3 with a series 1N4148 diode.

      keep the 100k to minimum level that this zero resistance, and connect it across the pin6 and pin3 (with a series 1N4148 diode, can be on side of the preset)

      now reduce the voltage to the lower threshold, and slowly adjust the 100k preset until the output of the opamp reverts to zero, switching OFF TIP122 and switching ON 2N2907)

      lower LED will be OFF, and upper LED will be ON now

  14. Hi Swa,
    As for the diode of 6A10, you are right, my mistake which over looked the diode lead. However, if the main DC is connected to the line on the pin #4, then how the battery will be getting charge?

    • …main DC (-) should be connected with the battery (-), and not with pin#4 line.

      6V4 is specifically for safeguarding the LED and the IC from a possible reverse battery polarity connection

        • Dear Anil,

          The requester had asked to provide a reverse polarity protection for the circuit, so the diode has been introduced for that, it is positioned for the circuit only, not the battery.

          the main negative from the adapter is supposed to be connected directly with the battery negative.

  15. Hi Swa,
    I have tried the simultion by using variable power supply on the battery terminal. When the 7.1V, i set the 10K to the position that the green led illuminated, i fixed the preset position. I adjust the variable PSU (the pretending battery) to 6.8V then the led went off, the TIP 127 was off
    Could you please help how to set to have 5.5V to initiate automatic charging?

    • Kanta, simulation will not help, you will have to build it practically and then set the parameters using a digital multimeter, that's the right way to go!!

      By the way where's TI127 in the above design, are you referring to TIP122??

  16. Hi Swa,
    I have several questions:
    1. With the 100K resistor as hysteresis control, what is the low level voltage for 6V battery to trigger the charging process. If the main power fail, what is the lowest voltage level for the battery will be to prevent it over discharging with this 100 K resistor?
    2. If the opamp IC is also controlling the over discharging and at the same time also control the over-charging to the battery, the TIP 127 will only conducting when the battery reach the desired high level voltage, hence, if the battery voltage slightly drop, the TIP 127 will be shutting off eventhough the battery voltage is still higher than the desired lowest voltage level? Let say the cut off fully charged battery for 6V battery is 7.1V, when the battery below 7.1V, the opamp IC will go down and 0 Volt come out from zener of pin #6 and it will shut down the TIP 127 eventhough the battery is still more than 6V?
    3. The diode (6A10) is preventing the ninus (-) battery going to the opamp IC and the whole system. Could you please explain where the system will get the minus (-) battery in the event the main power fails.
    I have bought all the materials to construct this emergency LED for 3 units. Awaiting your support soon. Thanks

    • Hi Kanta:

      1) You will need to find it by measuring the voltage at pin#3 for confirming the correct value of this resistor such that the discharging stops and charging initiates at the specified lower threshold voltage.

      The value should adjusted such that voltage the pin#3 just becomes lower than pin#2 at this lower threshold level. For this you can replacing the 100K with a 220K preset and with a 1K series resistor.

      2) The feedback resistor is introduced so that the charging stops at the 7.1V and initiates only at 5.5V

      3) the minus pole works in the opposite direction to the (+)

    • In point 2) did you mean to say that once recharging is initiated and the battery has charged to some point which is lower than the full charge level but higher than under-charge level, and during this time if the mains switches OFF, then the opamp will continue to keep the LED OFF….right?

      yes that's right this will happen unless some method is employed to rectify this. I'll try to upadte it soon.

  17. Hi Swa,

    Thanks for the prompt response. What is the minimum value of the capacitor, since the higher value, the bigger phisical size of the capacitor is.

  18. Hi Swa,
    I have 6V 5AH battery for this project. What is the correct DC Voltage from the main adaptor ?
    Can i just use 6V 1Amp transformer and bright rectifier without any regulator?

    • Hi Kanta,

      yes a 6V 1 amp trafo and bridge will do, make sure to use a high value filter capacitor and switch OFF the charger as soon as the battery terminal voltage reaches around 7.1V

  19. Hi sir if i use 12volt 7AH battery to connect 5nos 12 watt led,how many hour it will work? Do u have any method to calculte the time.

  20. hi sir. can i use 12volt 7.2 Ah battery in parallel for this circuit to run 5 of 12Volt ,12W LED or do i want make any changes in this circuit

    • Hi aariz, you can replace TIP122 with TIP142 and then proceed, however 12V 1.2AH will not be able to sustain a 5nos 12a watt LEd for more than 1/2 hour

  21. Hi Swa,

    If i want to equipe this with dark activated feature, can i just put a LDR in parallel to the collector and emitter (ground) of the BC 547.


    • Hi Kanta, no that won't do.

      Instead you could connect the LDR across the base of BC547 and the positive supply rail.

      And also make sure to connect a 10K resistor across base/emitter of the BC547

  22. Hi Mr Swagatam,

    I've got the idea, please bare with me, because i'm new to circuits design. i actually thought about using opams to create the circuit that i need, so that makes me feel better i was heading in the right direction. however, how can i update the circuit to operates on 26-30 volts and 3 amps. I'll be using a dc to dc voltage booster and steady current between the battery and this circuit, as the battery wont be able to supply the required voltage. so, im not sure if this circuit will still remain to operates with the voltage booster between the battery and the circuit. also, i will have another voltage booster to be connected the main power adapter as the adapter will only produce 19v and i need 26-30 volts. im kinda lost with this part because i need circuit to:

    1) as soon as i connect the external power automatically it will disconnect the battery and supply the system, in the mean while charging the battery.
    2) overcharging protection( which included in the above design).
    3) battery low and full charging indicates ( which included in the above design).
    4) also i don't know what is the formula to help how to determine the voltage required across my battery to charge it with( battery will be extracted of old laptops.total will be 22V with 6 apms at no load)
    5) also, i don,t know the formula to indicate how long my battery will last, and how to calculate the time if i want a battery to last me two hours.

    I'm sorry for those many questions, but i'm trying to get help and improve my skills in designing as i'm very new to electronics world.

    thank you very much.



    • Hi Mamdouh,

      boost converters are not easy circuits, and making two them will make the design unnecessarily complex and inefficient, so I won't recommend this idea.

      You can use a two 12V batts in series to achieve the 26V, and use a 26V adapter for the charging purpose, that will be much easier to configure.

      If possible I'll try to update the design as a new circuit using two opamps as requested by you soon

    • great, thanks for help.

      to give you a full perspective of the hole project. it's pretty much the same idea represented above.

      however, my led will be 100 watts consuming so it needs a steady power with current limited to 3 amps max.

      i will be added a heat sink with fan( a cpu heat sink with it's fan) to keep my led and component temperature under control.

      so it will:

      1) switch to turn the system on and off.
      2) off course my battery to supply the system in absent of external power and charging while external power is connected in the mean while supply the system.
      3) the whole safety thing for the battery.

      thank you very much.

  23. Hi Bro,
    Nice project.I want small changes in your project.
    a) I want to use three 1 watt leds in parallel in place of 5 watt led.
    b) Battery is 3 cell nimh pack 2500mAH.
    c) Charging source 5v adaptor 500mAH.
    Can i use these to my lamp?
    Can i use 3.3v zener in place of 3v zener?
    Please give reply soon.
    Thank you.

    • Thanks,

      You can use it with minor changes, please let me know what's the voltage rating of the NiMh cells, so that I can specify the alterations

    • Battery normal voltage is 3.6v,when fully charged it gives 4.4v at 2500mAH. till now I'm using it to connect directly to 3 1watt leds in parallel with individual 10 ohms resisters. this setup gives me 4hrs backup max. I wanted to make it automatic as mentioned in your above project.
      Thank you.

    • Surya, then you can use it without any change in the circuit except Rx, which can be calculated as per the given formula.

  24. Thanks a lot sir. . Got it as expected. .. ๐Ÿ™‚
    if possible may I get Component list separately. .
    lil blur over there so m asking sir hope you don't mind. .
    and also let me know Whether it's possible to add an inverter CKT of 50watt to run Light load like Cfl n charger. .
    Thank you

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