I'd like to know where one can get a 1500volt bipolar transistor with say a
25 watt dissipation rating at 1500volts Vce. Second breakdown kills bipolars
under these conditions - this is especially serious for shunt regulators.
For a shunt regulator, the transistor may need to be able to stand the full
supply voltage. Under transient conditions (first switching on) the voltage
across the transistor can be the full supply voltage until the loop has
worked. Since it won't have infinite bandwidth, it will take time for the
loop to stabilise - and this is unlikely to be under tens of microseconds.
This can probably be got around without too much complex circuitry. However,
high voltage transistors are relatively slow devices, so they need some
clamping. How long breakdown takes is interesting - the argument that you
can run a transistor such that you exceed Vcbo in a microwave PA because
there isn't time for breakdown to be established before the volts drop leads
to interesting arguments among process guys!
You can sink 30mA at 1kV in an 807. Surely they're still cheap enough?
73
Peter G3RZP
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