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I want to control resistance (100Mohm) programmatically. I found on this site that photoFET can solve this issue by sourcing constant current. From my understanding FET can give resistance control over orders of 1 to 2Mohm. Apart from this I want to drop 5000V dc(5kv) across this resistance. So what should I use? i.e Range of variation for this resistor needs to be from few 100 Megaohm to few kiloohms. A small amount of current 50 micro amperes flows in the circuit.

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  • \$\begingroup\$ Sounds hard. I assume a bunch of HV relays (to switch resistors) is too expensive. \$\endgroup\$ – George Herold Oct 8 '14 at 17:14
  • \$\begingroup\$ What is the min and max the resistance needs to be? Saying it needs to be 100 MOhm means you can use a fixed 100 MOhm resistor since it doesn't need to change. \$\endgroup\$ – Olin Lathrop Oct 8 '14 at 17:22
  • \$\begingroup\$ 100 Mohm to few kilo ohm range \$\endgroup\$ – sai Oct 8 '14 at 17:29
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    \$\begingroup\$ 5kV across 10k is 2500 watts. Have fun! \$\endgroup\$ – gbarry Oct 8 '14 at 17:38
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    \$\begingroup\$ It seems to me to that this could possibly work by using vacuum tubes, however, this is just an speculation since I'm not very well-versed in vacuum tubes. Perhaps someone with more knowledgeable could enlightened us. \$\endgroup\$ – Kvegaoro Oct 8 '14 at 18:16

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