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previous: Dave Stork You shouldn't have to use so much c... -- 11/22/1999 7:04 AM

Re: Bias circuit design?

11/22/1999 10:14 PM
Andrew	Re: Bias circuit design? I dunno Dave. I tried what you're suggesting, and it just doesn't seem to work like that (for reasons I don't quite understand). Either that or I don't understand your proposed calculation. Recalling what I built: 275VAC-100k-100湩(to gnd)-10k pot-27k-gnd 275*1.414 = ~390V (that's what I see on the scope, too) I was first tempted to just divide that by the total resistance in the circuit: 137k, yielding -108V on the cap. But I only see ~-40V there with the values above? In the end, it was just easier for me to tweak. I guess what was happening was that the forward flow of current through the diode is mostly provided by the capacitor, with only a little coming up through the 27k&pot? Seems then that the voltage would change a bit if I changed the capacitor, too? (I didn't try that). In the end there seems to be ~1mA coming up from ground through the resistor/pot. Thanks for the response. Cheers Andrew

11/22/1999 10:14 PM

Andrew

Re: Bias circuit design?

I dunno Dave. I tried what you're suggesting, and it just doesn't seem to work like that (for reasons I don't quite understand). Either that or I don't understand your proposed calculation.

Recalling what I built:
275VAC-100k-100湩(to gnd)-10k pot-27k-gnd

275*1.414 = ~390V (that's what I see on the scope, too)
I was first tempted to just divide that by the total resistance in the circuit: 137k, yielding -108V on the cap. But I only see ~-40V there with the values above?

In the end, it was just easier for me to tweak.

I guess what was happening was that the forward flow of current through the diode is mostly provided by the capacitor, with only a little coming up through the 27k&pot? Seems then that the voltage would change a bit if I changed the capacitor, too? (I didn't try that). In the end there seems to be ~1mA coming up from ground through the resistor/pot.

Thanks for the response.

Cheers
Andrew

Replies:

Gil Ayan q{Recalling what I built:27... -- 11/23/1999 7:32 PM