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-   -   const. voltage & const. current on output FET ? (http://www.diyaudio.com/forums/solid-state/68572-const-voltage-const-current-output-fet.html)

Bernhard 25th November 2005 11:13 AM

const. voltage & const. current on output FET ?
 
Would const. voltage Vds & const. current Ids on output FET reduce nonlinearity ?

5V @ 2A

jcx 25th November 2005 02:25 PM

certainly, keeping both constant also eliminates signal too

darkfenriz 25th November 2005 02:30 PM

Quote:

Would const. voltage Vds & const. current Ids on output FET reduce nonlinearity ?
If you mean cascodingthe constant current source, than YES, it basically increases output impedance and thus increases linearity at cost of voltage swing and maybe some other nasty things. But proper casoding may linearize, Pass wrote a nice article on this.

Bernhard 25th November 2005 04:17 PM

Quote:

Originally posted by darkfenriz

If you mean cascodingthe constant current source, than YES

I mean cascoding the gain device to keep the voltage constant.
But also keep the current through the gain device constant.

Steven 25th November 2005 07:18 PM

Stasis^2
 
I have a circuit concept ready for a single ended class A output stage that keeps both the current in the output transistor constant, as well as the voltage across it. It's basically an emitter follower (could be source follower) with some circuitry around it. The special thing is that the current remains constant irrespective of the load current. In this way Vbe is constant (or Vgs) and less distortion is expected.

If I only had time to finish the design.

Steven

Bernhard 25th November 2005 07:56 PM

Re: Stasis^2
 
Quote:

Originally posted by Steven
I have a circuit concept ready for a single ended class A output stage that keeps both the current in the output transistor constant, as well as the voltage across it. It's basically an emitter follower (could be source follower) with some circuitry around it. The special thing is that the current remains constant irrespective of the load current.

I made simulation too: SE classA with constant current & voltage on source follower.

What has Stasis got to do with it ?

Christer 25th November 2005 07:58 PM

Bernhard,
where does your load current come from?

Steven,
same question. :)

Bernhard 25th November 2005 08:15 PM

Modulated current source.
Parallel injection should also be possible.

Christer 25th November 2005 08:51 PM

Sure, there are many ways one could do it, but in the end you need something to provide the load current instead of the follower, so do you really gain anything? Maybe I just can't figure out a clever way to do it, but it seems you would probably make things more complex and probably get worse performance in the end. I'd be interested to see a schematic, though, of what you have in mind.

Steven 26th November 2005 01:01 PM

Re: Re: Stasis^2
 
Quote:

Originally posted by Bernhard

What has Stasis got to do with it ?

Stasis is the name Nelson Pass gave to his early amplifiers where the focus was on keeping the current through and the voltage across the transistors more or less constant. Stasis comes from Greek and means "a standing still", see http://dictionary.reference.com/word...002/08/04.html

Nelson used cascoding to keep the voltage more stable and Sziklai output pairs to keep the current through the driver transistors more stable (in a Sziklai pair the driver controls the output).

I called it Stasis^2 to indicate that my circuit keeps the voltage far more stable, as well as the current, but it is just a nickname; Stasis is a trademark, so I cannot use it.

Steven


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