The 723 regulator has some known reliability issues, but with proper
design they can be mitigated. In particular the differential voltage on
the error amplifier inputs is only rated for 5v. If one input is
connected to the 7.15V reference, then if the power supply output is
shorted the voltage rating is exceeded. The solution is a
strategically-placed diode.
Alan N1AL
On 07/22/2016 12:14 AM, Richard Fjeld wrote:
I was glad that I caught Jim's remark about blowing the 723 by being
connected to a battery with the PS off. And also Myron's answer.
Back in the tube TV days, I purchased a bare circuit board at Radio
Shack, (I think). The board was similar to an Astron circuit board, but
simpler. I rewound a heavy transformer from a color TV and made my
first 13.8 Volt power supply to use for a Heathkit HW-104. Years later,
the 723 went bad. It may have been due to the stated reason, I can't
remember now. I did some repair work on it and still have it.
Someone on the reflector provided the following link one time, which I
think is a good idea for an extra measure of over-voltage protection or
accidental reversal in polarity. I remember discussion about a reversal
that happened to someone on the reflector not long ago.
I hope the link still works on here. If it doesn't, it is on ad5x dot
com website. Look for a Vprotect pdf file.
http://ad5x.com/images/Articles/Vprotect.pdf
Dick, n0ce
On 7/21/2016 7:41 AM, Myron Schaffer wrote:
Jim and Clay,
It used to be that way....the RS linear models could not tolerate
external voltage present when unpowered, not anymore. Astron has
incorporated back-voltage protection through incorporation of some
diodes installed in key locations to prevent this.
You can verify if your supply has this modification by looking at the
circuit board and see a 1N4001 type diode soldered across 2-pins
(can't remember which ones off the top of my head) of the IC voltage
regulator LM-723 chip and others hung in various places to protect
the pass transistor as well. Usually soldered to the solder side of
the circuit board so they are easy to spot. I can't remember is there
were some small capacitors added as well.
Any newer (like newer than 1990) linear Astron will have these
installed.
Myron WVØH
Printed on Recycled Data
-
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