Hello, I know for a fact that LM338 as constant current source is flicker free as LED driver, but it heats up and is not power efficient. Size is another problem.

The Mean Well LDD-H is a box about 2 x 3 cm in size
http://www.meanwell.com/search/LDD-H/LDD-H-spec.pdf

The dimming is done by separate power source of >2.5 ~ 6VDC if I read data sheet correctly. But does it flicker?
So far the controllers I got from ebay do flicker (no you can't see it by eye) but a camera can see it.
As my project needs flicker free camera light source I would like to ask for help.

 

I would start by identifying the root cause of the problem. DC-DC converters are notorious for being unable to handle load transients. What is a load transient you ask? Glad you asked. If the current demand of the load changes suddenly, the voltage will drop, and the the DC-DC converter must adjust the duty cycle to adjust the average current output. This causes the output light to "flicker", or change in intensity.

Step one would be to establish why you have load transients at all. Step two would be to find a DC-DC converter with better transient response. Step 3 would be to design your own, if a suitable unit cannot be purchased. Last time I looked this kind of design expertise did not come cheap.

 

Thank you for quick response, as the load is LED the load is stable it does not change. I think I'm having bad luck with made in china led drivers.

 

If the LED driver output is unfiltered PWM, then adding a filter might help.

 

Thank you for quick response, as the load is LED the load is stable it does not change. I think I'm having bad luck with made in china led drivers.

Something is causing the poor regulation. You need to investigate more thoroughly to locate the root cause.