Re: 1% zener diodes?

On Jul 25, 10:05 am, Jim Thompson <To-Email-Use-The-Envelope-I...@My-
Web-Site.com> wrote:
On Wed, 25 Jul 2007 10:05:03 -0700, James Arthur
<dagmargoodb...@xxxxxxxxx> 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

.

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