sci.electronics.design

On Jul 25, 10:05 am, Jim Thompson > wrote:
> On Wed, 25 Jul 2007 10:05:03 -0700, James Arthur
> wrote:

[...]

> >In practice, +30v and two cascaded zener shunt regulators did pretty
> >well, but you could also do something like this:
> >(view in Courier font)
>
> > .-----------------------------.
> > | |
> > | |
> > .-. |
> > | | R1 |
> > | | (trim for |\ |
> > '-' desired iz) | \ |
> > | | \ |
> > +----------------|+ \ |
> > | | \-------o-------> Vout
> > | | / |
> >,---' .--------|- / |
> > / \ ZD1 | | / |
> > --- | | / .-.
> > | | |/ | | R2 (trim for
> > | | | | desired Vout)
> > === | '-'
> > GND | |
> > '---------------------+
> > |
> > .-.
> > | |R3
> > | |
> > '-'
> > |
> > |
> > ===
> > GND
>
> >I think the above circuit's even self-starting if you choose an op-amp
> >with sufficiently high bias currents and use low-enough valued
> >feedback resistors. Otherwise, throw on a starter.
>
> >Cheers,
> >James Arthur
>
> 741 (and some brands of 709) OpAmp's will self-start in this
> configuration. I built hybrid circuits using this circuit between
> 1970 and 1973 at Dickson Electronics. Other OpAmp's may NOT
> necessarily self-start. So I handled that problem with a
> resistor/disconnect-diode scheme.
>
> ...Jim Thompson

Well, I was thinking of the LM324, what with its PNP inputs, not to
mention fabulous precision & noise ;-), but there are others...

Oh, sheesh ... okay, you've shamed me into it:

"Bootstrapped reference with startup"

Vcc
-+-
| .-----------------------------.
| | |
| | |
.-. .-. |
| |R4 | | R1 |
| | | | (trim for |\ |
'-' '-' desired iz) | \ |
| D1 | | \ |
V1-> +--|>|--o----------------|+ \ |
[*] | | | \-------o-------> Vout
.-. | | / |
| |R5 ,---' .--------|- / |
| | / \ ZD1 | | / |
| | --- | | / .-.
'-' | | |/ | | R2 (trim for
| | | | | desired Vout)
=== === | '-'
GND GND | |
'---------------------+
|
.-.
[*] V1 < V(ZD1) | |R3
| |
'-'
|
|
===
GND

Cheers,
James Arthur