Vasile Surducan wrote:
>
> On Fri, 26 Jan 2001, Michael Rigby-Jones wrote:
>
> > > -----Original Message-----
> > > From: Roman Black [SMTP:fastvid@EZY.NET.AU]
> > > Sent: Friday, January 26, 2001 10:04 AM
> > > To:   PICLIST@MITVMA.MIT.EDU
> > > Subject:      Re: [EE:] Shunt regulator? 317/337 solution
> > >
> > >
> > > As I said, a shunt regulator needs positive feedback,
> > > ie; if voltage is too high, must turn on more.
>
>     I'm agree with this only if "regulator" means for you the final
> transistor of a shunt regulator. But the effect of regulation comes
> because of the global negative feedback. If you have a NPN driven in base
> from an operational amplifier you must connect +in to feedback and -in to
> reference to achieve a shunt regulator. Colector of the npn conected to
> load and balast resistor to V+. But this is not a positive
> feedback. Increasing output voltage level will determine the amplifier to
> turn on more the transistor and the final effect is the output voltage
> will decrease at initial value ( assuming you have a good reference )
> In any language we are talking about this is negative feedback !
>
> > > The actual inversion is provided by the nature
> > > of it being a shunt reg.
> > >
> > > I really don't think you can do it with a 317,
>
>     Well, the ideea was to do it with a 317. Of course is neither the
> cheapest nor the best methode. But can be done in some circumstances.
> Don't shut the piano player just because you don't like how it sing !
> And if you don't think make first a try.
> Cheers, Vasile

Sorry Vasile! I should have said it in a different way.
I know you knew what I meant! :o)
-Roman

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