I need to power many 100w 32-36V LEDs… and building loads of 32V PSUs is costly and time consuming.
This is a bit of a crazy idea, and I'm aware that it's probably not the safest way to do this, but this circuit has just popped into my head:
The tiny detail that I'm not quite sure about is the DC voltage after the rectifier:
- Should I calculate using 240V, so 7 LEDs connected in series across 240V would give 34.2V per LED.
- Or, should I calculate using the peak, non-RMS voltage 340v, so 10 LEDs connected in series across 340V would give 34V per LED.
N.B. I'm aware the picture shows 8 LEDs, but it's just to visualise what I'm talking about.
If anybody has any other quick, easy, safer ways to do this then please let me know!
Best Answer
The circuit you have drawn will not do what you want. If I were going about things this way, this is what I would do:
simulate this circuit – Schematic created using CircuitLab
How you implement the current sink is up to you. You could have a simple current sense resistor + feedback driving a linear pass transistor (if you want to dissipate lots of heat). If this is passing 3A (which is roughly what those LEDs are pulling) and has to drop 10V of extra voltage, that's 30W of heat you need to dump off into a heatsink. Not impossible, but requires thought. You can see the basic design of a linear current sink here.
You could also implement a current-controlled buck converter for the LEDs - although rating this for the full rectified mains voltage will require consideration. The link in @Damien's comment above is a good place to start looking, specifically using something like the Fairchild FL7701. This would be much more efficient, but requires a more sophisticated design.