LED DRIVER assistance required?

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.

steveastrouk11 months ago

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
m3ngc (author) 11 months ago

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

steveastrouk m3ngc11 months ago

How is it, temperature wise for you ?

m3ngc (author)  steveastrouk11 months ago

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.

mpilchfamily11 months ago

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.