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Re: pinging triode kingdom

Posted by Dave Cigna (A) on May 5, 2007 at 04:46:24

In Reply to: pinging triode kingdom posted by Vinnie on May 4, 2007 at 13:51:34:

Vinnie, I don't believe that there is any formula for calculating the size of the resistors given just the size of the caps. As Ian (Gingertube) suggested, it really is a function of leakage current. As he said, you want the resistors to pass at least several times as much current as the DC leakage current of the caps. More current will work fine, but it means that you'll be wasting power from the ps. Sometimes someone wants to deliberately bleed a certain amount of current anyway (for some other reason) so they let the cap balancing resistors perform double duty. In that case the resistors might be passing far more current than necessary to keep the caps balanced, but that's OK.

The fact is, I think you should be able to figure out what's happening all by yourself. That's the very best way to learn... To understand it yourself, I suggest you think about what you would expect to see with only the resistors in place. Leave the caps completely out of the picture for now.

Here's a homework problem. If you work through it then I guarantee that you will be left with a much better understanding. I strongly suggest you try to find the answers by yourself before asking for help. Obviously, you are free to use any books. Everything you need is probably in the first chapter or two of the National Radio Institute Home Study Course that your wife gave you.

Homework problem:

On a piece of paper, draw a string of three 150k resistors in series with 1000VDC at one end and ground at the other.

1. Calculate the net resistance of the entire string.

2. Calculate the current through the string.

3. Calculate the expected voltage at each junction (i.e. the voltage across each resistor.)

4. Calculate the total power dissipated by the entire string.

5. Calculate the power dissipated by each individual resistor.

-- Dave

p.s. Please, I'd like to ask that others do not shout out their answers before Vinnie has a chance to figure them out himself.

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