Sorry to be pushy, I'd love some feedback on this. This is prety much a repost from the end of my previous thread.
After going over pretty much every post in the forum relating to constant current sources, I found
https://www.electro-tech-online.com/threads/high-power-led-controller.95832/ which has some interesting design ideas.
I slightly extended the idea to work over the range I am interested in, ie rectified AC, in the following schematic. Is the design correct?
**broken link removed**
The zener voltage could be reduced to accommodate maximum gate voltage,
R8 would be used as sense resistor to create drop Vref at 20mA in my case but I guess R = Vref / I in the general case.
At 20mA with Vref being 2.5V, Heat losses in the sense resistor are .05W, which is acceptable.
I guess R6 and R7 need dimensioned, and I probably need advice on that, as I believe they are actually the critical bit of the design, in term of responsiveness and stability.
With R6 at 300k, I should get a bit less than 1mA at 300V , which feels like enough to feed the gate. (and I happen to have a reel of 1206 100k that could be put to good use there)
R7 should limit the rise speed, I am not sure of which value would do, but i suspect it is very much a wet finger estimate type of thing. Maybe an extra 100k?
Would that work?
Thank you in advance for your answers.