DIYbanter - View Single Post - Chinese dimmer just had thermal runaway and burned up

Ralph Mowery

In article ,
says...

That's it, no more Chinese dimmers! I just can't trust them. This
week, I managed to pick up a linear variable voltage and current Astron
12 amp power supply. It won't be as efficient as switching units, but
Astron is apparently a winner with amateur radio folks and reviews tout
its reliability. I looked at the schematic and it seems that all of
their units use the same general design, just different transformers and
components of course as size increases. I like the fact that the
schematics are readily available unlike this Chinese stuff where it is
next to impossible to find one! I have even been able to peek at
several internally online of course, but apparently people often tweak
and modify them and post images and such online. Nice to see the innards.

Astron has been using the same basic design for many years for their
linear supplies. There is almost no difference in any of them, just
more pass transistors and bigger transformers. That same circit has
been used in many other power supplies with minor variations. All
designed around the 723 voltage regulator. It is almost like a
cockroach and the circuit will not die as it is very reliable.

I have a 50 amp one that has been on 24/7 for around 30 years. Only cut
off when I moved and to rearange the equiipment.

They do have two weakness in that if you push their ratings the
transistor socket pins get loose and do not make good contact.
If the power is cut off and right back on say as can hapen during a
storm the over voltage protection will trip and you have to cut it
off,count to about 10 slow and then turn it back on.

I have another supply of no name that uses the same basic circuit and it
has been on over 40 years.