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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