I do high level simulations of video decoding cores.
I want to design a dichromic led lighting system for plants.
blue can be done with high power leds, I ll worry about those later.
660nm (far red) has to be generated from 20mA leds.
My ultimate goal in this project is to get some SMPS design, to handle the load (probably chains of 200 of those leds, at 450V, 20mA), but before that I need to go trough a bunch of steps.
I got to the point where I can generate board designs good enough for non critical designs (like a buch of leds in series), and half decent power circuits. I am getting stuff for etching slowly.
I wish to design a wide voltage range linear current regulator to test individual led modules to start with. I'd like to use some of the power bjt or mosfets I salvaged from PC power supplies (which I can get for free for personal use from work)
**broken link removed**
Are there any caveats with these types of currrent regulators ?
Current spikes on start, poor regulation?
I was thinking about using voltage regulators with a resistance in series and the adjust pin tied after the resistor, but they do not seem to come with breakdown voltages higher than 125V.
Considering that the transistors come for free, I'd be quite interested to get some use out of them.
As I understand, the gain for the BJT I got is about 10, Vbe=7V
As such, Ibe should boe 2mA for 20mA load current intensity,
With a supply voltage of 200-300V, and a 20V zener, R1 should let 4mA go trough, so with a voltage over the resistor of 180-280, we are talking 45k resistor max. This would need to dissipate 2.37W at 280V. Not impossible, but annoying.
The transistor would have to dissipate 6W which is perfectly in spec, and I have large aluminium heatsinks that should take the abuse without problem.
If I go with the mosfet, I suspect I will be able to greatly increase R1 as gate current should be mostly for charging the gate and compensating for gate leakage, which hopefully is not much on these big ones. I need to research this, but I suspect I should be able to get away with 500K, which would get power under the cheap hobbyist .25W limit.
Any comments?
Am I talking rubbish?
All inputs appreciated
Thanks.
Ps: How do you guys attach pictures to your posts, free web image hosting is somehow suboptimal.