Capacitance multiplier, suggest improvements

AllenB · 03:59 AM

I have this supply ready to power a dual rail class A amp. Can this circuit give low ripple, and hold a steady ground for low DC offset?

(EDIT: The lower rail in the picture should read -V, of course

)

MJL21193 · 28th February 2011, 04:08 AM

It won't work as drawn. Look HERE for some idea. - post #14 details a cap multi regulated supply that you can look at the structure of.

RJM1 · 04:10 AM

More like this.
And the bottom supply should be labeled V-.

MJL21193 · 28th February 2011, 04:09 AM

Yeah, that doesn't fix it.

RJM1 · 28th February 2011, 04:11 AM

Yeah it does.

MJL21193 · 28th February 2011, 04:20 AM

Quote:

Originally Posted by RJM1

Yeah it does.

No, it doesn't.

RJM1 · 28th February 2011, 04:27 AM

Yeah it does.

AllenB · 28th February 2011, 04:30 AM

Yes, thanks, I can get it to sim now. Is it OK as a practical circuit?

MJL, that's a monster you have there.

Elvee · 28th February 2011, 09:20 AM

Quote:

Originally Posted by AllenB

I have this supply ready to power a dual rail class A amp. Can this circuit give low ripple, and hold a steady ground for low DC offset?

(EDIT: The lower rail in the picture should read -V, of course

)

You should add resistors in parallel with the capacitors, to give the transistors more room.

Substituting a CFP for the darlington has a number of advantages: it improves the ripple rejection marginally, gives a DC output 0.7V higher, but more importantly, it reduces the output impedance by a factor 2.5.

AndrewT · 28th February 2011, 10:15 AM

the added resistor parallel to the base cap is what makes it a capacitor multiplier.
Without the added resistor, the circuit tries to be a bad voltage regulator.

That added resistor !
Try a series pair of Zener and resistor. You can get cap multiplier action where output voltage tracks (a fixed % of ) input voltage at voltages lower than the "knee".
At input voltages higher than the "knee" the slope of output voltage vs input voltage brings in a little voltage regulation and this prevents excessively high voltages being sent to the client circuit when mains voltage is near maximum tolerance.

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28th February 2011, 04:08 AM	#2
MJL21193 Account disabled at member's request Join Date: Mar 2007	It won't work as drawn. Look HERE for some idea. - post #14 details a cap multi regulated supply that you can look at the structure of.

28th February 2011, 04:09 AM	#4
MJL21193 Account disabled at member's request Join Date: Mar 2007	Yeah, that doesn't fix it.

28th February 2011, 04:11 AM	#5
RJM1 diyAudio Member Join Date: Jan 2010 Location: Titusville, Fl.	Yeah it does.

28th February 2011, 04:30 AM	#8
AllenB diyAudio Member Join Date: Oct 2008	Yes, thanks, I can get it to sim now. Is it OK as a practical circuit? MJL, that's a monster you have there.

28th February 2011, 10:15 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	the added resistor parallel to the base cap is what makes it a capacitor multiplier. Without the added resistor, the circuit tries to be a bad voltage regulator. That added resistor ! Try a series pair of Zener and resistor. You can get cap multiplier action where output voltage tracks (a fixed % of ) input voltage at voltages lower than the "knee". At input voltages higher than the "knee" the slope of output voltage vs input voltage brings in a little voltage regulation and this prevents excessively high voltages being sent to the client circuit when mains voltage is near maximum tolerance.