[SOLVED] LED Driver Different Behaviour with different LED Color

[Batur]

Hi,

I am trying to drive single 30W chinese leds using the below circuit but using 12V vcc:



Vf of the leds are 12V and I want to keep Led curent about 2.3A. However while I can drive the white led without a problem, blue and UV leds whose specs (Vf,Iled) are identical do not drive more than 1.5A and 0.2A respectively.

When I connect the leds directly to 12V both draw nearly 3A, TPS16500 is a boost driver so i thought maybe input voltage was not enough so increased it to 15V but there is no change in the current. My supply can provide nearly 10A so I dont think its limiting the current (also white led has no problems).

I think my circuit is somehow limiting the current but I cant find the cause. The driver is not running very hot, current sense resistor is adjusted for 4A. Any help would be greatly appreciated.

Best Regards

 

[KlausST]

Hi,

the circuit is a step up (boost) driver... so you less input voltage than the LED voltage...

Either your overvoltage protection becomes active, or the 5V supply is overload (dropping voltage)

Klaus

 

[andre_luis]

When I connect the leds directly to 12V both draw nearly 3A, TPS16500 is a boost driver so i thought maybe input voltage was not enough so increased it to 15V but there is no change in the current

What are the values you selected for each component of the above figure ?
Note: This is TPS61500, not TPS16500.

 

[Batur]

Sorry for the late reply, I changed the layout of the board and the problem is solved. I minimized the distance between diode and switching pins, and also made the whole bottom copper layer ground.