Re: Modify Astron Power Supply

: The diagram looks strange to me, with a direct connection from the
: higher voltage driver supply (e.g. pin 12 of the 723 or collector of
: Q2) to the base of the series pass transistors.

The pass transistor pre-drive transistor is a simple current amplifier.

: With a higher separate driver power supply the driver current should
: flow through the Q2 driver transistor, through the small resistors
: into the base connection of the series pass transistor. Thus in the
: diagram the direct connection from the driver supply to the series
: pass transistor base should be removed.

Some of the available circuit diagrams have mistakes...

:>I modded one of those significantly. Too long ago to remember the exact
:>thing I did, but DO put that crowbar SCR anode on the collector of the
:>pass transistors. If it trips as is, you kiss the current meter and
:>expensive current sense resistor goodbye.

: When using crowbars, there should be a some kind of fuse on the
: feeding side, preferably immediately after the filter capacitor.

No, you want the entire supply to remove itself from operation if
the crow-bar circuit fires.

: If the crowbar is before the series pass transistors, it is a good
: idea to put a large reverse biased diode across the series transistors
: (CR7 in the diagram), which would discharge any large capacitors on
: the regulated side through the crowbar. Without the diode, the
: collector side would be at 0 V after the crowbar tripped, but the
: emitters could still be at +12 V due to any large capacitors on the
: regulated side.

An expensive part... the crow-bar is best left at the tail end of the
supply (where it is now).

cheers,
s.

.

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