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Old 11th July 2012, 12:18 PM   #1641
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Quote:
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Yes, I had run noise sims with 220uF and 200R. It can be a bigger cap for lower impedance depending how effective you wanna be for below 1/f noise knee.
So double C and half R (like 440uF and 100 ohm) would give the same frequency knee ??
And higher C, and same R - for better 1/f noise knee

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Keep in mind that an non damped big cap can stretch semis during on/off there will be a practical threshold for each Vo level they could take.
2)
Do you mean that the big cap will unload charge through the Vref-chain, and give a high peak-current, Io? I tried to analyze it, and i cant see how - since basically the Current at on/off is the same as the normal working current, and is limited by R103:

in my understanding the size of the peak-current isnt determined by C. It is I = Io*exp(-t / RC). So C only determines the length of the peak.

Io is limited by the resistor, so Io = Vr / R103
Now asuming the chain is R + Zener:
- then Vr (V over R103) = Vtotal - V(zener)
- which basically gives the same Io as normal working current, determined by Idss of K117.

So if you make R103 less and C bigger, - Io stays the same, because V(zener) has to be bigger.

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Old 11th July 2012, 04:15 PM   #1642
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1. Yes for filtering effect. Noise knee 1/F point is defined by the semis physics.
2. I had kills of 25V JXXX JFETs at the base of Vref in high Vo & high cap experiments.
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Old 11th July 2012, 08:24 PM   #1643
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First you got to get rid of the cables to the Mosfets. Only local PCB fit. You got wrong shape sinks for easy side or bottom fit I see.
OK I changed them - mosfets are soldered right to the board, but no change - now I get 3.6V instead of 3.7V. Any other ideas?
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Old 11th July 2012, 08:31 PM   #1644
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That had to be done, OK. 3.6V spells VGS potential only. See if you got any voltage drop across the outermost trimmer pins.
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Old 11th July 2012, 08:40 PM   #1645
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That had to be done, OK. 3.6V spells VGS potential only. See if you got any voltage drop across the outermost trimmer pins.
Only 0.189V, which at the current trimmer position gives about the same 0.1mA through the trimmer as I had through R103 before.
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Old 11th July 2012, 08:42 PM   #1646
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What happens if you will short the trimmer with a wire for a test?
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Old 11th July 2012, 08:51 PM   #1647
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What happens if you will short the trimmer with a wire for a test?
Still 3.6V.
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Old 11th July 2012, 09:03 PM   #1648
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Is Q304 a BC550? Is it flanked by a couple of 2SK117s?
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Old 11th July 2012, 09:11 PM   #1649
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If yes, does Q304 measure ~0.6V Vbe? Is R304 1 Ohm and not 1 kOhm by mistake?
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Old 11th July 2012, 09:12 PM   #1650
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Yes on both counts for the parts. The "1 ohm" resistors from Teabag's kit measured 1.2 ohms, but I figured they were close enough. I'll check Q304.

Last edited by schubert; 11th July 2012 at 09:14 PM.
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