"Big Bad Bob" wrote in message
...
On 12/28/18 09:16, bitrex wrote:
All amps of that scale should have active protection circuitry/monitoring
of currents, biases, and temperatures via microprocessor to avoid
potentially catastrophic faults.
Even briefly overvolt or overcurrent on a typical transistor, and you'll be
replacing it VERY soon. I made the mistake of designing a circuit that
operated close to the maximum Vceo (these 60V transistors should be able to
handle 45-50V right?), and the transistors never lasted long under load
(replaced 3 times, and 3 blown fuses that were supposed to protect them).
Replaced with transistors that had twice the Vceo and no problem.
Well... overcurrent on a mosfet output device is usually pretty safe for
quite a while. Second breakdown is the problem with bipolar. Their rating at
high voltage is much lower than their power ratings would imply.
I designed mosfet amp in the early 80s. I tested it by putting in a full
level signal with an output s/c. The only protection was a zener across the
gates to limit the current to the device ratings. I left it cycling with its
90 Deg heatsink thermal cutout for 3 days. No problems.
-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html