40 Watt LED Emergency Tubelight

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 read 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 40 watt street light circuit article. You can refer it for knowing more about its circuit functioning.

Automatic Battery Charger Circuit

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.

Need Help? Please send your queries through Comments for quick replies!


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.

Swagatam said…
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.
Swagatam said…
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 specs...in 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.
Ashok Dhenge said…
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: ashokdhenge06@gmail.com
Swagatam said…
Please refer to the following post:


Remove the transformer power supply and replace it with solar panel input
style said…
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.
Swagatam said…
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.
Swagatam said…
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.

Contact me for Customized Circuits


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