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Gyrators to replace PSU chokes?
Gyrators to replace PSU chokes?
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Old 1st May 2010, 04:36 AM   #1
ray_moth is offline ray_moth  Indonesia
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Default Gyrators to replace PSU chokes?

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!
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Old 1st May 2010, 12:47 PM   #2
Eli Duttman is offline Eli Duttman  United States
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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.
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Old 1st May 2010, 06:11 PM   #3
Leffemannen is offline Leffemannen  Sweden
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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
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Old 1st May 2010, 06:54 PM   #4
Michael Koster is offline Michael Koster  United States
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Quote:
Originally Posted by Leffemannen View Post
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
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Old 2nd May 2010, 03:16 AM   #5
ray_moth is offline ray_moth  Indonesia
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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.
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Old 2nd May 2010, 06:34 AM   #6
Wavebourn is offline Wavebourn  United States
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Gyrators to replace PSU chokes?
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.
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Old 2nd May 2010, 10:25 AM   #7
pointy is offline pointy  United Kingdom
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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.
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Old 2nd May 2010, 12:13 PM   #8
ray_moth is offline ray_moth  Indonesia
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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?

Last edited by ray_moth; 2nd May 2010 at 12:18 PM.
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Old 2nd May 2010, 03:34 PM   #9
Bas Horneman is offline Bas Horneman  Netherlands
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Electronic Choke
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Old 2nd May 2010, 04:39 PM   #10
revintage is offline revintage
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Did some sims on Leffemannens circuit and that one is ca 25H.
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