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

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