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Old 28th February 2011, 03:56 AM   #1
AllenB is offline AllenB  Australia
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Default Capacitance multiplier, suggest improvements

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 )
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Old 28th February 2011, 04:08 AM   #2
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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.
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Old 28th February 2011, 04:08 AM   #3
RJM1 is offline RJM1  United States
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More like this.
And the bottom supply should be labeled V-.
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Old 28th February 2011, 04:09 AM   #4
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Yeah, that doesn't fix it.
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Old 28th February 2011, 04:11 AM   #5
RJM1 is offline RJM1  United States
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Yeah it does.
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Old 28th February 2011, 04:20 AM   #6
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Quote:
Originally Posted by RJM1 View Post
Yeah it does.
No, it doesn't.
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Old 28th February 2011, 04:27 AM   #7
RJM1 is offline RJM1  United States
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Yeah it does.
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Old 28th February 2011, 04:30 AM   #8
AllenB is offline AllenB  Australia
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Yes, thanks, I can get it to sim now. Is it OK as a practical circuit?

MJL, that's a monster you have there.
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Old 28th February 2011, 09:20 AM   #9
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by AllenB View Post
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.
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Old 28th February 2011, 10:15 AM   #10
AndrewT is offline AndrewT  Scotland
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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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