Gyrators to replace PSU chokes?

[ray_moth]

PSU chokes are bulky and heavy and not necessarily well made unless expensive. Gyrators seem to offer a tempting alternative, but can they effectively replace PSU chokes? Comments welcome!

[Eli Duttman]

Ray,

Gyrators are definitely useful. Everything has its price. You need Volts to operate the circuitry. So, no gyrator in place of a true inductor, when constructing a choke I/P filter. Still, a gyrator allows you to emulate a large inductance, while using comparatively little space and adding little weight.

Check this page (written in German) out.

[Leffemannen]

I use it as filter in my PSU, works like a charm. Just that it dose not store energy like a true choke do.

shematic

The middle one is B+ supply (we have 230 mains -> 1:1 120VA transformer: I get about 295 volt DC @ 230 mA out)

The bottom one is the -60 volt (negative) supply, that's why it's upside down. (I like to keep the mosfet close to ground when ever possible)

/Leif

[Michael Koster]

Originally Posted by Leffemannen

I use it as filter in my PSU, works like a charm. Just that it dose not store energy like a true choke do.

shematic

The middle one is B+ supply (we have 230 mains -> 1:1 120VA transformer: I get about 295 volt DC @ 230 mA out)

The bottom one is the -60 volt (negative) supply, that's why it's upside down. (I like to keep the mosfet close to ground when ever possible)

/Leif

Might not be a bad idea to add a gate-source zener diode for gate voltage protection to these circuits.

Cheers,

Michael

[ray_moth]

Thanks for the information. Can anyone explain how to calculate the simulated inductance for a MOSFET gyrator? Would an IRF820 be OK? I'm thinking of using it in a stereo EL34 PP amp.

[Wavebourn]

Unfortunately gyrator can't replace a choke. A choke stores an energy, while gyrator turns it into a heat simulating inductive impedance. If to make a tank out of gyrator and a capacitor it may have low output impedance on the main frequency, but for other frequencies it's output resistance will be higher. It is better to utilize the same elements and to make a R-C filter with a big time constant, and a source follower.

[pointy]

I was taught to only control the output of any one valve section in one way (volts or current)

so that the VALVE will form the audio signal of that section

in this way the one side (volts or current) can be laid flat for the valve to form a good image of the audio signal with the other

this practice stops solid state from forming part of the audio signal output of any stage and this requirement will be different from the voltage gain stage to the current output stage of an amplifier

so I would look to have each valve section controlled at point in only one way.

[ray_moth]

Sorry, Pointy, I can't see the relevance to a gyrator in a PS.
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PS: I still don't understand how to estimate the simulated inductance -- can anyone suggest a formula based on the simple MOSFET circuit in the German site linked by Eli?

[Bas Horneman]

Electronic Choke

[revintage]

Did some sims on Leffemannens circuit and that one is ca 25H.