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Decker 2nd January 2006 08:10 PM

Zen Variations Part 3: regulated supply question
I'm building the bipolar version of the Zen regulated supply for an amp project. I have a question about Figure 6 from the Zen Variations 3 article: does the PNP Mosfet Q2 in that diagram have the source and drain connections reversed, or is it correct as printed? Figure 7 has the same layout. I'm scratching my head over this one, so any help would be appreciated.

GRollins 3rd January 2006 12:12 AM

The IRFP9240 (Q2) in Figure 6 is drawn upside-down. Ditto for Q2 & Q4 in Figure 7.
When hooked up correctly, the pass device would present its Source to the load (instead of its Drain), thus becoming a follower.
If you're going the bipolar route, you could always use the Zener stack to set the reference for a driver transistor--whether bipolar or MOSFET--and use that to drive non-Darlington pass devices...but the circuit would get more complex. Just depends on what you have on hand.


P.S.: MOSFETs are generally referred to as "N-channel" or "P-channel" instead of NPN or PNP like bipolars. The IRFP9240 is a P-ch device.

jh6you 3rd January 2006 12:15 AM

Refer to Fig.7.
Drain of N-Channel MOSFET (IRF240) sees +53V and its Source sees +45V.
Drain of P-Channel MOSFET (IRF9240) sees -45V and its Source sees -53V.
Both Drains have higher voltages than Sources (This is my clue to the avoidance of confusion.).


flg 3rd January 2006 01:46 AM

"avoidance of confusion." ???
"Both Drains have higher voltages than Sources" ???
I'm getting confused now... My figure 7 agrees with what Grey said... Q2 and Q4 are up-side-down... But then, -45V could be considered "higher" than -53V:D :D :D Perspectives perspectives. As my Grandma used to say "to each his own".

jh6you 3rd January 2006 04:31 AM

Oh my God . . . :bawling:

You are right Q2 and Q4 upside down.
And -53 is negatively higher than -45.

Full shame on me from the first day of new year.
I will stop my poor post from today. Bye bye.

Happy new year.


GeorgeBoles 3rd January 2006 09:57 AM

A slightly different Zen 3 power supply question
Hello everyone,

My question is slightly different. I have been going to ask this for a while but didn't think it important enough to start a new thread!

Regarding the Zen 3 power supply, the statement is that at least the simplest version (Figure 1) is not suitable for Class AB or B amplifiers.


This figure is not particularly great as a regulator, and ordinarily we
would look to improve on it, usually by enclosing the regulator transistor
in a feedback loop to correct for this variation. If this were a higher
power Class B or AB type amplifier, such an output impedance could
easily result in one or two Volts of nonlinear distortion signal in the power
supply, and this would bleed into the output circuit as distortion.
Is that true for the final versions, i.e. for Figures 2, 6 and 7?

If figure 6 and 7 are suitable for Class A and AB amplifiers, this would be a really simple and useful circuit!

What do you think Mr. Pass meant?



Decker 4th January 2006 12:25 AM

Thanks, GR!

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