Need current regulator circuit for 300 vdc, 1 mA

Discussion in 'The Projects Forum' started by Greg52556, Dec 7, 2014.

1. Greg52556 Thread Starter New Member

Dec 7, 2014
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0
Anyone know of a circuit (or component) to regulate my 300 vdc to 1 mA as the load decreases? I am doing electrolysis and the load decreases as the process continues, due to ion formation.

Nov 12, 2008
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3. Greg52556 Thread Starter New Member

Dec 7, 2014
4
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OK. Source is 300 vdc, R1 is 10 kΩ, R2 depends on what I want to limit current to, the transistors are like BC547 and BD139 except they will be 500 volts. Did I miss anything? Thanks!

4. crutschow Expert

Mar 14, 2008
13,496
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You forgot power dissipation. At 300V a 10k ohm resistor will draw 30mA and dissipate 9W so you will want to increase R2's value. Since you only need 1mA, you could increase R2 to about 10meg ohm or so.

5. Greg52556 Thread Starter New Member

Dec 7, 2014
4
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So to confirm:
R1 stays at 10k ohm.
R2 should be 10 meg ohm.
This limits current to 1 mA with 300 vdc source.
What wattage should R1 and R2 be?

Last edited: Dec 8, 2014
6. JWHassler Member

Sep 25, 2013
204
34
I think the resistor ref-#s got swapped: R1 is the larger one. 10 megohms sounds good and will dissipate .009 Watts
R2 sets the current by R2=600/current_in_mA (approx 600 ohms) and dissipates .001*600 = .6 Watts

7. crutschow Expert

Mar 14, 2008
13,496
3,373
Yes, I meant R1 of course.

Note that the 600 ohm R2 emitter resistor will dissipate .001^2 * 600 = .6mW.

Last edited: Dec 8, 2014
8. JWHassler Member

Sep 25, 2013
204
34
Oh gosh..... right back atcha, crutschow.

9. Greg52556 Thread Starter New Member

Dec 7, 2014
4
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Thanks! I'll let you know how it works.