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Old 8th January 2004, 06:15 PM   #1
olvrkrg is offline olvrkrg  Germany
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Default Constant current source -3000V

Hello,
for an amplifier projekt I'm looking for a constant current source
10-30mA but -3000V. A series of 1000 V MOSFETs for example? Any suggestions?

Best regards
oliver
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Old 8th January 2004, 11:05 PM   #2
sreten is offline sreten  United Kingdom
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Is this an attempt to be amusing ?

sreten.
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Old 9th January 2004, 07:10 AM   #3
olvrkrg is offline olvrkrg  Germany
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No, definetely it's serious !
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Old 9th January 2004, 12:33 PM   #4
sreten is offline sreten  United Kingdom
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OK, I'll bite, why 3KV ?
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Old 9th January 2004, 12:51 PM   #5
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Maybe you should tell what voltage variations you expect on
the 3kV, since it might matter for the choice of solution. It is
quite a difference if you expect max 100V or max 1kV variation.
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Old 9th January 2004, 01:34 PM   #6
maylar is offline maylar  United States
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Need to know the input voltage range and also the load voltage and whether or not the load can become shorted.
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dave
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Old 9th January 2004, 03:08 PM   #7
olvrkrg is offline olvrkrg  Germany
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Excuse me that I did not tell more details before. I have build this amplifier to drive electrostatic loudspeakers. In the final stage, two tetrodes (4x150a) with anode resistor (120k, 40W) work as well known anode amplifier, push pull to drive the two stators of the electrostatic loudspeaker. Voltage supply ist +3000V, anode quiescant voltage +1500, swing ist +500 to +2500, for example.
The problem ist, that resistors of this kind in good quality are very expensive and my one is composed of 40 metal film resistors...
It is already working, but now I like to do some improvements.
So I thought, why not try a constant current source instead of the resistors?
Many thanks for your interest in my "ideas"

Best regards
oliver
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Old 9th January 2004, 04:30 PM   #8
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from first hand experience (ham radio stuff and photomultipliers) I can tell you that very peculiar stuff starts to happen when you go over about 700 volts -- things like humidity, presence of dirt, proximity, non-linearity of resistors etc.

You probably want to rethink using standard PCB materials, insulations etc. You can also wire bipolar devices in series -- there's an example in "the art of electronics".

BTW, Kepco sells replacement MOSFET devices for their very high voltage supplies -- used by the folks at Oak Ridge and Lawrence Livermore Labs, places like that --
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Old 10th January 2004, 02:18 AM   #9
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Two words:
Tubes
Cascode
You can cascode current sources, and tubes make fine current sources. Stack two (or more) tubes on top of one another in a cascode and you can deal with truly prodigious voltages.
Real world example? The front end in the Atmasphere amps. They use cascoded 6SN7s as the current source for the differential. Granted, the voltage is a lot lower, but the concept is what you're after.

Grey
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Old 10th January 2004, 09:17 AM   #10
Jax is offline Jax  Sweden
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Why not use another 4x150a to form an SRPP circuit?
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