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-   -   Simple opamp/mosfet shunt regulator (http://www.diyaudio.com/forums/solid-state/139825-simple-opamp-mosfet-shunt-regulator.html)

Bonsai 5th March 2009 08:43 AM

BTW - its important to add the RC filter to th e zener reference as I mentioned above because the zener is quite noisy.

dodo 5th March 2009 08:49 AM

I don't know exact impendance of the used Zener reference
But assuming it's around -150 ohm . , if I made my math correctly 220R should be used insted of 499 to ensure eqiuval impendance on both imputs of the eror opamp

So before any final statment ...... we should ask the author about the base of his calculations

dodo 5th March 2009 09:04 AM

2 Attachment(s)
Bonsai

Do you have any bad expirience with the large ( 1000uF) low ESR cap on the autput of the shunt regulator ?



BTW , Borbely Simple Shunt

analog_sa 5th March 2009 10:22 AM

Just curious why would you want such a large cap at the output of a high performance regulator? One of the best reasons for using regulators i have is to minimise capacitance close to the amplifiying devices and thus large capacitor sound.

Rtop84 5th March 2009 10:39 AM

Big low ESR caps aren't optimal choice for high NFB opamp based regulators. Damping with small SMD resistor is usful. Somebody will say that better way is put in high ESR cap, but damped low ESR cap sounds otherwise than high ESR one;) but only experimental selection of caps and value of resistor in concrete circuit gives the best results...

iko 5th March 2009 12:04 PM

2 Attachment(s)
Quote:

Originally posted by analog_sa

Can you publish CCS results alone?

What is the purpose of R15?

Sorry, I don't understand what you mean by "CCS results alone."

As was said, R15 and C5 were intended originally as a filter for the zener noise, in the Jung regulator, except that the in+ to the opamp was taken from between R15 and C5, as in the next picture.

Edit: psrr curve with 1000u as the output cap.

iko 5th March 2009 12:08 PM

2 Attachment(s)
To filter the zener noise as in the Jung regulator, see attached. The psrr remains unchanged. I will have to do more sims to see if everything else stays the same.

Rtop84 5th March 2009 12:12 PM

PSRR plot always will be good;)....transient response with low esr cap is problematic.

Bonsai 5th March 2009 01:05 PM

With your latest circuit, PSSR will remain unchanged. What will improve is the output noise because you have filtered the noisy Zener.

Re the use of a big output cap. I prefer to use as big a cap as possible to keep the output impeadance low - especially at higher frequnceis where the open loop gain of the op-amp reduces. However, you have to watch that you do not introduce a pole in the loop with a low ESR cap - so this is where you have to try th e caps out to make sure the regulator remains stable.

I think some of the results we are getting in the sims are probably not acheivable (one sim showed better than -200dB!), but you should be able to get a a good, improved result.

Salas 5th March 2009 01:30 PM

Quote:

Originally posted by ikoflexer
salas, you're too kind, but I think that it's too early for congrats.

Anyway, I thought I stop poluting your threads

To the contrary, your ideas and simulations are shared wealth and stimulation. I don't believe that any idea or tweak is pollution. Good luck with the practical employment and measurements. It owes to sound it too. I would be glad to make one and subjectively ***** it when its final, and maybe there is a PCB.


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