# Variable current circuit for High Power LED

Discussion in 'The Projects Forum' started by soumitrak, Nov 27, 2017.

1. ### soumitrak Thread Starter New Member

Sep 27, 2017
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0
Specs of LED(BXRA-56C5300H 50W) are 23.5 Vf and 2.1 A typical current.
Led max rated current is 4 A @ 28.5 V only for pusling at 10% duty cycle.

My actual project has 64 such LEDs and will be powered with 24 V 67 A DC supply to 32 such LEDS so equivalent 2.09 A current for each LED string connected in parallel to supply.

I want the LED should be operating at this rated current of 2.1 A for 99% of time and must be able to switch (digitally controllable) must draw 4A with 10% duty cycle and switch back to regular 2.1 A current.

I do have heatsinks for these LEDs as they will be dissipating lot of heat. Can anyone suggest me circuit for this and explain .

Thank you!

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2. ### crutschow Expert

Mar 14, 2008
21,383
6,125
For 4A you need 28.5V.
How do you want to generate that voltage?

3. ### soumitrak Thread Starter New Member

Sep 27, 2017
9
0

I have three 12 V 150 AH SLA Batteries which can be use to obtain 28.5 V with appropriate circuit

4. ### Sensacell Moderator

Jun 19, 2012
2,196
707
It would be helpful to see a diagram of your proposed system?

If you intend to parallel connect two COB modules, you will find they share current very unevenly, this can lead to thermal runaway and rapid failure.

Look at the data sheet current Vs. Vf curves p.14, you see the Vf varies all over the place.
The hotter one will have a lower Vf, it will hog more current and get hotter... Poof. Dead.

5. ### soumitrak Thread Starter New Member

Sep 27, 2017
9
0

I have attached circuit for one LED but I intend to extend to use this for total LED of 64 . Since LED is current controlled device should I worry about controlling current drawn from battery rather than its voltage and current limiting resistor value for 4 A each LED string .

I am open to other suggestion if please highlight if there is any mistake in my approach I am trying to learn

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