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LED DRIVER assistance required? Answered

I am trying a diy led build. I have 9 3w 4v 800mah high power leds and a  240v AC to 26-39v variable voltage DC 1500mAh fixed  driver.
My first question is, if I connect my 9 leds in series =36v leaving 3v drop do I need to limit the fixed 1500mAh current and if so how.
My second question, is there a way of fitting a dimming circuit given that I cannot access the internals of the driver.

I have looked for answers but cannot find oe specific to my problem

Many thanks in advance for replies.


Yes, you need to regulate the current. You need to use a constant current regulator, but the classic circuit might not work, but its worth a try.

Here's the circuit. You need to put the LM317 on a good heat sink, and you probably want a 1W resistor, the one marked OR5 should be 1R5, 1.5 ohms for you. This circuit will dim for you, but get hotter in the process.

trimmable current source.JPG

4 years ago

Thanks to mpilchfamily and steveastrouk for assisting me. I used the LM317 circuit to good effect.

How is it, temperature wise for you ?

Changed the 1w resistor for a 3w and runs much cooler and may upgrade the LM317 to I think it is an LM350, but I will see how it goes.

Use an LED to figure out the resistor you will need to help limit the current. Though it's best if you have a driver made for these LEDs that is made to offer a constant current that the LEDs need.