see the picture in attachment
I have a LED driver in front of it,
Yeah, it is one of those extremely cheap ones (http://www.aliexpress.com/item//1973332388.html). It works just fine.. unless you want to PWM it . So the problem is in the driver?
I have swapped the led and power supply and dimming works just fine, so the problem is in the power supply.
I'm just thinking: What if I put some bigger cap parallel between the TIP120 and the power supply? That should cover the time while it is not delivering the current and thus allow me to do the PWM.
When I tested the circuit I used a salvaged PC power supply (with 12V 10W LED instead of those 30V I'm using with drivers). And it just worked!
Are there any risks of doing that pernament? I'm speaking of connecting the 12V LEDs straight to the DC12V of the power supply (and switching it with TIP 120...).
I'm having a feeling that I should connect a resistor in series with the led, but what if the voltages are equal?