A note on my background: I do have a degree in electrical engineering, but honestly I don't consider myself skilled enough to come up with designs from scratch, hence my post.
I wish to design a light panel consisting of 3 sub-panels (interleaved) with red, green and blue LEDs respectively. Each sub-panel shall consist of 12 pcs of 1W high-intensity LEDs. I plan to build a separate LED driver circuit for each sub-panel. Hence, I need to find a suitable design for a driver circuit to replicate and deploy in three copies.
Requirements / Features
- 1W LEDs (Typical specs: Vfwd = 3.0 to 3.4 V, I = 350mA)
- 12 VDC power supply - so the LEDs must be in a series-and-parallel configuration. I guess multiple 'strings' (N=4) with 3 leds in each should be fine.
- Each string should be driven by a constant current circuit. If possible, I would prefer to adjust the current in all strings from a single point (e.g. by adjusting/replacing a single resistor)
- I wish to be able to dim the (sub-)panel from a microcontroller using PWM.
- If possible, would like to keep the component count reasonably low.
What's a good design for a driver circuit fulfilling the features above? I have tried to find an answer in this forum, and elsewhere, but without luck.
For the best that I know, the following circuit should be a good starting point:
The circuit above features constant current supply and enable PWM-control, BUT, I can't see how to extend to multiple strings of LEDs. I have been thinking of incorporating some kind of current mirror, like below, but I can't figure how.
My questions are:
- Can I extend the circuit, as per the first figure, to support multiple strings of LEDs? How?
- Are there any better/more appropriate designs that I should/could use instead?