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.
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.
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
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
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.
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.
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.
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?
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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?
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Here:
Active Choke for Valve Amplifiers
Gyrators can indeed take the place of smoothing chokes. The circuit shown in the link is current limited to about 50mA, but you can increase the zener to 12V, and R3 to 10 ohms to get up to 200mA dc continuous, with a clip-on heatsink.
(You can even make a gyrator-input rectifier if you isolate the gyrator with diodes, although I can't see much point in such a topology.)
Ray,
Forgot your question about simulation. It´s quite easy if you do it by trial and error:
Do two models with the same capacitors.
Do first wih a choke and the other substituting the choke with a gyrator.
Then apply the same DC-voltage with added ripple.
Try out what choke-value gives equal ripple as the gyrator one.
You can use the .step directive to find the right value.
A more accurate method is to do a frequency response plot of the gyrator and then work out the inductance from the resonant frequency:
L = (1/2*pi*f)^2 / C
.
You mean put it in say a series resonant circuit with a known C value and do a frequency vs impedance plot?
Wouldn't it be easier to plot the gyrator impedance vs frequency and calculate L based on the -3db cutoff frequency?
With the MOSFET based gyrator circuits I build there is a simple RC that determines the Fc. I usually calculate the -3db point in circuit and don't even worry about the equivalent inductance.
If it's a power supply filter, you can use a constant-voltage-referenced follower and get both ripple reduction and regulation with the same pass element.
Cheers,
Michael
I looked at Gyrators a while back and A couple of things come to mind with regards to their use
(1) A Gyrator does not store energy like an inductor.
(2) because they don't store energy, they will dissipate more heat to achieve the same voltage drop.
With these in mind, wouldn't one achieve better PSRR (assuming the goal is to reduce ripple for lower IM and hum) using the transistor as a series regulator rather than as a Gyrator?
The simulations I've done with the gyrator show higher ripple than the simple pass regulator with not many more components. The pass regulator does require a larger input filter cap as a trade off.
An additional advantage of a true inductor is the result of their storing energy. It is possible to take a transformer whose ratings are with a capacitive input filter, change it to an inductive input filter and then draw a greater amount of current at a lower voltage.
(1) A Gyrator does not store energy like an inductor.
(2) because they don't store energy, they will dissipate more heat to achieve the same voltage drop.
With these in mind, wouldn't one achieve better PSRR (assuming the goal is to reduce ripple for lower IM and hum) using the transistor as a series regulator rather than as a Gyrator?
The simulations I've done with the gyrator show higher ripple than the simple pass regulator with not many more components. The pass regulator does require a larger input filter cap as a trade off.
An additional advantage of a true inductor is the result of their storing energy. It is possible to take a transformer whose ratings are with a capacitive input filter, change it to an inductive input filter and then draw a greater amount of current at a lower voltage.
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Something like that, yes. I was thinking of a Gain V. Frequency plot really, which will show a resonant peak just like any LC filter stage. Impedance v. frequency would work too though.
Exactly. A series stabiliser can give better performance, but needs a larger / high-voltage capacitor.
Tubes can be used as filter reactor (chokes) in power supplies,the concept is not new and there even was a type especially designed for that application: the CBS 6216.
This small 9-pin miniature high perveance beam power pentode can actually replace a 12H/100mA/350DCR filter choke in a power supply,as illustrated in this 1953 CBS ad below:
More common (high perveance) tubes could be substituted in this circuit with similar results. For many reasons, the 6216 and associated filter reactor circuit remained obscure and was seldom used. My guess is that the good old choke was cheaper,more reliable and easier to implement...
This small 9-pin miniature high perveance beam power pentode can actually replace a 12H/100mA/350DCR filter choke in a power supply,as illustrated in this 1953 CBS ad below:
More common (high perveance) tubes could be substituted in this circuit with similar results. For many reasons, the 6216 and associated filter reactor circuit remained obscure and was seldom used. My guess is that the good old choke was cheaper,more reliable and easier to implement...
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