Hello to all members.
And also remember that properly applied, a Zener diode can be a very
good reference. This might be more in the Volt--Nuts class, but the
Solartron 7081 8.5 digit DVM uses a TC Zener as a voltage reference. Of
course it is a selected Zener with a carefully controlled bias current
and assorted compensation tricks, but still a Zener for a lab class 8.5
digit DVM.
Nice and safe holidays,
Claude VA2 HDD
On 2021-12-26 12:49, ed breya wrote:
Andy wrote:
"... I too was surprised to see nothing more than a Zener being used
in one case, but bearing in mind this was in a temperature controlled
environment is not as bad as a Zener in open air."
In the OCXOs I've had opened up, they used a temperature compensated
Zener, typically in the 1N821 class, 6.2 V, or one near 9.1 V (I
forget the part number series). So, it could actually have a very good
overall tempco - a TC Zener operating at a fixed oven temperature.
These were directly regulating the internal circuit voltage, and not
buffered, so I think the main problem with stability is the external
loading effects on the operating point of the TCZD. I think the first
noticeable effect would be a drop from open-circuit reference voltage,
when hooking up an external pot.
Ed
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