Re: Modifications to 577 Curve Tracer Main Power Supply


 

On Sun, Mar 1, 2020 at 11:04 PM, Gary Robert Bosworth wrote:


The reason why I do not like this design is because of the fact that the
-30V output is used to bias the 6.2V reference diode VR772. This poses a
classic lock-up condition in that if the -30V does not exist, then the
reference diode is never turned on.
I think that's incorrect:
Whenever - 40 V is present, Q788 is pulled into conduction by R787 (to gnd), causing the output voltage to move from 0 V towards - 30 V.
The regulating circuit *reduces* that conduction by increasing conduction of Q786.

Raymond

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