Nov 27, 2012

40 Watt LED Emergency Tubelight Circuit Using 1 Watt 350 mA LEDs

The article explains a simple yet effective 40 watt LED emergency tube light circuit which can be installed at home for acquiring  uninterruptible illumination at the same time saving a lot of electricity and money.

You might have reads one of my earlier articles which explained a 40 watt LED street light system. The power saving concept is pretty much the same, through a PWM circuit, however the alignment of the LEDs has been laid in a completely different manner here.

As the name suggest the present idea is of an LED tube light and therefore the LEds have been configured in a straight horizontal pattern for better and efficient light distribution.

The circuit also features an optional emergency battery back up system which may be employed for getting an uninterruptible illumination from the LEDs even during the absence of normal mains AC. Due to the PWM  circuit the acquired backup can extend up to more than 25 hours on every single recharge of the battery (rated at 12V/25AH).

The PCB would be strictly needed for assembling the LEDs. The PCB must be an aluminum-back type. The track layout is shown in the below given picture. As can be seen the LEDs are spaced at a distance of about 2.5 cm or 25mm from each other for enhancing maximum and optimal distribution of light.

Either the LEDs may be laid over a single row or over a couple of rows.

A single row pattern is shown in the below given layout, due to lack of space only two series/parallel connection has been accommodated,  the pattern is continued further on the right side of the PCB so that all the 40 LEDs become included.

Normally the proposed 40 watt LED tube light circuit, or in other words the PWM circuit may be powered through any standard 12V/3amp SMPS unit for the sake of compactness and decent looks.

After assembling the above board, the output wires should be connected to the below shown PWM circuit, across the transistor collector and positive. The supply voltage should be provided from any standard SMPS adapter as mentioned in the above section of the article. The LED trip will instantly light up illuminating the premise with flood light brightness. The illumination may be assumed to be equivalent to a 40 watt FTL with power consumption of less than 12 watts, that's a lot of power saved.

Emergency Battery Operation

If an emergency backup is preferred for the above circuit, it may be simply done by adding the following circuit.

Let's try to understand the design in more details:

The circuit shown above is the PWM controlled 40 watt LED lamp circuit, the circuit has been elaborately explained in this article. You can refer it for knowing more about its circuit functioning.

The next figure shown below is an automatic under voltage and over voltage battery charger circuit with automatic relay changeovers. The whole functioning may be understood with the following points:

The IC 741 has been configured as a low/high battery voltage sensor and it activates the adjoining relay connected to the transistor BC547 appropriately.

Assume the mains to be present and the battery to be partially discharged. The voltage from the AC/DC SMPS reaches the battery through the N/C contacts of the upper relay which remains in an deactivated position because of the battery voltage which may be below the full charge threshold level, let's assume the full charge level to be 14.3V (set by the 10K preset).

Since the lower relay coil is connected to the SMPS voltage, stays activated such that the SMPS supply reaches the PWM 40 watt LED driver via the N/O contacts of the lower relay.

Thus the LEDs remains switched ON by using the DC from the mains operated SMPS adapter, also the battery continues to get charged as explained above.

Once the battery gets fully charged, the output of the IC741 goes high, activating the relay driver stage, the upper relay switches and instantly connects the battery with the N/C of the lower relay, positioning the battery in the standby condition.

However until AC mains is present, the lower relay is unable to deactivate and therefore the above voltage from the charged battery is not able to reach the LED board.

Now if suppose AC mains fails, the lower relay contact shifts to the N/C point, instantly connects the supply from the battery to the PWM LED circuit, illuminating the 40 watt LEDs brightly.

The LEDs consume battery power until either the battery falls below the low voltage threshold or mains power is restored.

The low battery threshold setting is done by adjusting the feedback preset 100K across the pin3 and pin6 of the IC741.


  1. Hi, it is a good one, can we have the 12V smps circuit for this.

    Housing this LED and protecting it from eyes is the catch here. is there a design detail about putting this unit in a housing. may be a Acrl glass sheet be used.

    1. Thanks!

      A readymade SMPS unit can be used here for simplicity, because the tube light part is itself quite lengthy and complex, we do not want to make the unit anymore complex.

      Any standard readymade enclosure can be incorporated or simply the entire LEd strip may be directed toward the ceiling which will produce a reflected light from the roof, safeguarding the eyes of the residents.

    2. OK, Sir, thank you, i shall make an enclosure and test it, if found to be good , shall share the same in this blog

  2. do u have any circuit about measuring inrush current for lighting eq. ?

    1. If you could explain your requirement a little more elaborately then probably I would be able to design it for you.

  3. how much max wattage solar panel and max ampire battery can i use with circuit
    and can u please modify and update this circuit with 10 amp battery and 100 watt max solar panel support

    1. The above circuit is not intended for solar panel, however if you incorporate a solar charge controller then you can feed the voltage to the SMPS points. Solar panel can be anything from 60 to 200 watts and the battery can be upto 50 AH.

      The link diagram specifies a solar panel of 7Amp, which can never charge a 100 to 300 AH fact it's suitable for a 10 AH battery, just make the shunt transistor collector resistor to 2 Ohms each

  4. Hi Swagatam,
    Thanks for your prompt response to design a circuit which is inline to my requirements. Again I do have some queries.
    1. Here you have mentioned to use 12v/25Ah batteries and they will last for 25 hours on a single charge. It is okay for me to have this setup give me 6-8 hours backup. Kindly help me in modifying the circuit where ever necessary.

    2. Secondly, I plan to have this circuit built on 230v straight bypassing the battery part thereby using the above circuit for replacing the tube light with the PWM circuit as you have mentioned of the low power consumption.


    1. Hi Nagaraj,

      As mentioned in the article, if the emergency part is not required the circuit may be powered directly through an AC/DC power supply 12V/3 amps, it may be an SMPS or a transformer type PS.

      For backups you can use any 12 battery, the backup time will depend on the AH of the battery.

  5. Hello, the second circuit dosent can u please help me, i cant calibrate it , i tried it withe a variable power supply when the voltage drops below 4.5 volts the relay shuts down and i dont know how to set the 10k presaet (charging) please help to calibrate it

    1. 10 preset is for high voltage cut off and the 100K preset is for the low voltage activation.

      Apply 14.2 volts and adjust 10K preset so that the relay just activates.

      Then reduce the voltage to 11.5 and adjust 100K preset such that the relay activates back.

  6. Hi swagatam,

    Can u tell me what will be power consumption of a circuit with serial connected leds.. (two leds are connected in serial, and a total of 10 strings)

    Led type : white 8mm wide angle led (straw hat type)
    Leds Forward voltage: 3.4
    Current: 100 ma
    No of serial strings : 10 (each Serial string is connected parallel to the power supply )

    No of leds per string : 2

    Total no of leds : 20
    so.. how to calculate power consumption of this circuit.. !

    How many watts ?

    1. Hi Bibin,

      Each string will consume current depending upon the series resistor value.

      so please tell me what resistor you have connected with each series.

    2. hi swagatam,

      The power supply was 6v 5ah battery.. so i didnt connect any series resistor.. !

    3. swagatam... led current is 30ma not 100ma .. sorry... !

    4. Hi Bibin,

      Please check the formula given in the following article, you may use it for finding current, resistance value and power consumption for any LED series.


  7. Hai swagatam,

    Thanx for ur great circuit.can I use 6v 4.5ah battery.if yes what are the modifications.

    1. Hi Thanks very much!

      6V will work but you would have to reduce the LED to one on each series, rest everything can be kept as it is. The series resistors now becomes around 7 Ohms

    2. Thank u very much sir

  8. Hi Sir Swagatam
    can i use this into my motorcycle as an additional lighting accessories? Is there any changes in the circuit component? Thanks in advance sir.

    1. Yes, surely it can be changes would be required.

  9. Swagatam
    could u provided a 220v somewhere 60 to 90 led (3.5v) circuit diagram which look like a tube light type

    1. You can try this circuit, connect all the 60---90 LEDs in series:

  10. Dear Swagatam,

    In the PCB layout for the LEDs given above, I think there is a mistake. The power supply from the PWM circuit directly connects to the first LED and in turn the rest two LEDs are connected in series with the first one with the resistor in between. But in the circuit diagram, the supply is fed to the LEDs via the resistor. kindly clear my doubt.


    1. Dear Nagaraj,

      Both the diagrams are correct, the resistor can be put anywhere in the line of the series.

  11. Dear Swagatam,

    I want to use 9 to 12 1 watt LED's and 4volts 1.2 AH batteries with a quantity of 3 Nos.
    Please advice a circuit with uninterruptible illumination of LED Light in the presence and Absence of AC 220 V input supply.Also please let me know the DC powersupply output voltage to drive the LED's
    what circuit will you advice me.
    Thanks in Advance
    Please reply me at (
    Regards/Faisal Mateen

    1. Dear Faisal,

      A 1.2AH batt will support only 1 to 2nos 1 watt leds, so your idea won't be feasible.

  12. Please advice a circuit with uninterruptible illumination of LED Light in the presence and Absence of AC 220 V input.
    i can use 3 Batteries of 1.2 AH in series so i will get 12 VDC.
    Actually these betteries are very low cost here so i want to use it.
    And i only need a backup of 2 to 3 Hours .

    1. you can try this circuit:

  13. Dear Swagtam sir,
    Can you tell me that by using 1 watt power led can i make led tube light of 20 to 25 leds which will work on ac supply. plz tell me required ckt.


    1. Hi Yogesh,

      Yes you can do it but you will have to use a AC/DC converter power supply for driving them, direct AC supply will blow them of.

    2. Pardon my being a novice who has been so much interested in electronics but has no way of having been into it. Please am so sorry to bother you with the following questions. I want to build the device urgently. So i will appreciate if you could kindly answer the questions all the questions for me.
      Please could you kindly tell me what is SMPS unit/adapter?
      What is PCB?
      How many are the LEDs and how do i split the LED into 2 or 3 sections each?

      In the second diagram, under Emergency Battery Operation: where would the 12volts negative and positive be connected?

      Lastly, for the automatic under voltage and over voltage battery charger circuit , please what does the connection to the 12VDC from SMPS means. And the connection to PWM circuit? Wont the charger be connected to electric mains (220)

    3. Here are the answers to your questions:

      SMPS units are power supply units readily available in the market and are used for converting mains 220V or 120V domestic AC to the desired DC voltage such as 3V, 6V, 9V, 12V etc as per the specifications.

      For our circuit we require a 12V smps.

      These are also rated with according to their current limit our case we require a 2 to 3 amp smps (12V)

      In the first diagram 3nos LEDs are connected in series with an individual resistor, for getting around 40 watt fluorescent equivalent illumination we need at least 10 to 12nos of such strings connected in parallel as shown in the the first diagram.

      In the second diagram the smps positive input is connected to the relay N/C contact of the relay and the negative is connected to the line which joins with pin#4 of the IC 741.

      As explained above the smps 12v DC output which is derived from the AC mains is connected across the indicated "SMPS input" points in the diagram.

  14. Swagatam
    i made this Low/ high voltage circuit i used for solar panel charger controller input with 12 volt 7.2 ah battery . still i dont tested because i have some question from schematic diagram because i want some changes like;
    1: when input power from solar panel charger is active then load cut and charge continues
    2: Input fails to charge then load contunies till discharge point.
    my question is that ,
    1: When led glow?
    2:How to preset set for low discharge point.
    mail me:

    1. Please refer to the following post:

      Remove the transformer power supply and replace it with solar panel input

  15. Sir,
    What do you mean by aluminium back PCB .is it available in market.. I have knowledge of hard board or acrylic back PCB.
    Why using PWM circuit. Wat is led rating.. Can I use SMD LEDs.

    1. It's a PCB with an embedded aluminum base which acts like a heatsink for the soldered LEDs, it could be available readymade in the market as per individual preferences.

      The PWM circuit is only for dimming purpose, may be eliminated if the dimming feature is not required.

  16. Hi.. I really appreciate your efforts and commitment through this blog. I would like to include a battery backup either with nicd or 4v lead acid batteries in multiple counts to support a recently bought led tube light of 18w. I would like this to be concealed within the t5 fixture. Pls suggest a circuit design that auto charges and backs up lighting when power fails with no or minimal wiring change at home.

    1. Hi, thanks!

      I think the circuit shown in the following link will suit your application:

      the transformer power supply can be replaced with any standard 12V adapter followed by a 7805 IC for supplying the battery under charge.


Swagatam Majumdar
Swagatam MajumdarHi Friends, Welcome to my site, a place where you will discover a massive collection of electronic circuit ideas, mostly requested by the dedicated readers and exclusively designed by me for their customized application needs. I have posted more than 1100 circuit designs in this site, if you have a personalized circuit requirement you may feel free to request it through the comment box, if it seems feasible to me then surely you may find it published here with your credentials attached in the post, thanks and please keep reading

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