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The Singing Bush
The Singing Bush
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Old 4th April 2020, 06:22 PM   #411
Zen Mod is offline Zen Mod  Serbia
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The Singing Bush
Originally Posted by lhquam View Post
Here are some startup waveforms corresponding to the circuit in post #406. The horizontal scale is .2s/div.
  • violet is Vds(M1) at 20V/div
  • yellow is V+ at 20V/div
  • blue is V- at 5V/div
  • cyan is Vs(M1) (M1 source pin) at 20V/div
  • Vd(J1) is slightly less than Vs(M1).
The simulation in post #406 agree fairly well with these measurements.
tnx lhquam

and tnx for special Singing Bush picture you sent me in e-mail

regarding Singing Bush - as I already described - SIT biasing circuit is faster than Mu, so during startup procedure SIT is already biased in moment when Mu is starting conduction ........ so Mu is seeing (almost ) full rail voltage while current being 0 ...... then as current is rising, Mu Puck Vds is decreasing........

so , highest Vds is (almost) rail voltage , while highest current is pre-set Iq, luckily ( 'twas a Cunning Plan) never happening in same time
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Last edited by Zen Mod; 4th April 2020 at 06:24 PM.
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Old 4th April 2020, 07:28 PM   #412
lhquam is offline lhquam  United States
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Yes, that is a big advantage with having a separate power supply for the SIT bias circuit. I strongly considered that when designing my PCBs, and would do it for future designs.

I just looked at my PCB artwork and at trivial mod, cutting one trace and adding a wire to an unused Molex connector pin would allow using a separate supply for V-. The only other change would be to reduce one cap in the bias circuit from 1mF to around 22uF.

Last edited by lhquam; 4th April 2020 at 07:35 PM.
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