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previous: Daver Amps that have series filter caps h... -- 12/28/1999 1:42 AM

Re: Power Supply Resistors

12/28/1999 5:54 AM
Bruce	Re: Power Supply Resistors It never hurts to have some positive way to bleed a filter cap off and it also helps (albeit minor) with the regulation. Think of Ohm's Law here, I don't know the voltage of the circuit you are using so here is another way to look at this. If you want to limit the current across a 1 watt bleeder resistor to say, .5ma to 1ma then you can use this: R = P/I^2 R = 1w/.001a x.001a R = 1w/.000001a R= 1M R = 1/.0005^2... R = 5M I don't know how long it would take a 1M to 5M resistor to bleed off, say 400vdc out of a 22uF cap, but I'd guess too way long. Ha ha... the smaller the resistance value, the shorter time to drain the supply off. So, I'd just use a 1W to 2W 360K to 470K metal oxide resistor and be done with it. More Ohm's Law... 400v/470K = .000851a .000851a x 400v = .34 watts 400v/360K = .0011a .0011a x 400v = .44 watts A 1 watter will work OK but 2 watter will probably last a lifetime. Bruce

12/28/1999 5:54 AM

Bruce

Re: Power Supply Resistors

It never hurts to have some positive way to bleed a filter cap off and it also helps (albeit minor) with the regulation.
Think of Ohm's Law here,
I don't know the voltage of the circuit you are using so here is another way to look at this.
If you want to limit the current across a 1 watt bleeder resistor to say, .5ma to 1ma then you can use this:
R = P/I^2

R = 1w/.001a x.001a
R = 1w/.000001a
R= 1M

R = 1/.0005^2... R = 5M

I don't know how long it would take a 1M to 5M resistor to bleed off, say 400vdc out of a 22uF cap, but I'd guess too way long. Ha ha... the smaller the resistance value, the shorter time to drain the supply off.
So, I'd just use a 1W to 2W 360K to 470K metal oxide resistor and be done with it.

More Ohm's Law...

400v/470K = .000851a
.000851a x 400v = .34 watts

400v/360K = .0011a
.0011a x 400v = .44 watts

A 1 watter will work OK but 2 watter will probably last a lifetime.

Bruce

Replies:

Daver Outstanding, Bruce! That's just wha... -- 12/29/1999 12:03 AM