[AMPS] screen regulators

[km1h@juno.com]

On Mon, 16 Nov 1998 15:11:37 -0000 Peter Chadwick
<Peter_Chadwick@mitel.com> writes:
>
>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?

Hollow state still works Peter! Particularly when cost and reliability is
a factor.
I have used triode connected 6L6, 807, 6146, 829B/3E29, 5894, etc in the
past. Just parallel what you need for current. 
In this area 829B's and sockets are almost throwaways at flea markets.

For serious voltage you can use all those 4CX250 pulls and the cheap
Russian/Chinese sockets. Old GE Master Pro TX sections with the 8072
final are found in dumpsters.
HP and other companies use the 4CX250, 8072 and similar in HV lab
supplies. 

73  Carl  KM1H

 
>
>73
>
>Peter G3RZP
>
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