RE: 4 pole caps in a voltage doubler circuit

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Posted by Gingertube (A) on July 30, 2012 at 21:05:05

In Reply to: 4 pole caps in a voltage doubler circuit posted by DAK on July 29, 2012 at 17:28:20:

Yes you can use them. The extra lugs ("poles") are just to get a low inductance connection to the external circuit. In switch mode power supplies switching at 100s of kHz that is very important. Can't hurt for an audio amp. I have a bag of 470uF/450V caps (inherited from the day job) with 4 terminals like these.

Like any voltage doubler make sure the "top" caps do not have an exposed case connected to the -ve terminal which in a voltage doubler circuit will sit at half rail voltage, got a nasty surprise from a cheap Chinese 845 SET which had dergraded insulation on the "top" cap (Half rail was 440V).
Series connecting caps for both top and bottom positions is OK, ALWAYS use voltage share resistors across series connected caps. Make sure the voltage share resistors are appropriate value - biggest mistake I see with posted designs using series connected caps is using way too high a value share resistor value.

Work out the typical leakage current from the formulae on the data sheet or if not given use the following:
Ileak = 0.006 CV
where C is the capacitance value (in Farads) and V is the applied voltage (not the caps rated voltage) and then size the the resistor such that you get at least 3 times that leakage current in the share resitor ( 5 times is better). Then do an I squared R calc to get the power dissipated and use a resitor of at least 3 times that power rating.

Example Calc:
assume your caps are 1000uF 160V and you will have 130V applied
leakage current from above will be 0.8mA.
Want 5 x 0.8 = 4mA in the share resistor, 130V across it so 27K share resitor is what you need. I squared R gives you 0.43 watts, use a 2W metal film minimum.

Hope this helps,
Cheers,
Ian

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Follow Ups Full Thread

Topic - 4 pole caps in a voltage doubler circuit - DAK 17:28:20 07/29/12 (14)

RE: 4 pole caps in a voltage doubler circuit - Gingertube 21:05:05 07/30/12 (1)

thank you for the info (nt) - DAK 01:41:38 07/31/12 (0)

RE: 4 pole caps in a voltage doubler circuit - mikeyb 11:01:15 07/30/12 (1)

RE: 4 pole caps in a voltage doubler circuit - DAK 18:45:50 07/30/12 (0)

RE: 4 pole caps in a voltage doubler circuit - Chris O 18:24:08 07/29/12 (9)

RE: 4 pole caps in a voltage doubler circuit - Eli Duttman 18:55:00 07/29/12 (8)

hash filter - DAK 08:56:32 08/01/12 (0)

" Insert a "hash" filter" - Chris O 07:54:30 07/30/12 (6)

RE: " Insert a "hash" filter" - mikeyb 10:52:37 07/30/12 (1)

RE: " Insert a "hash" filter" - Jim McShane 09:22:32 07/31/12 (0)

RE: " Insert a "hash" filter" - Jim McShane 10:49:45 07/30/12 (3)

RE: " Insert a "hash" filter" - Gingertube 21:14:52 07/30/12 (2)

RE: " Insert a "hash" filter" - Eli Duttman 17:10:35 07/31/12 (0)

I ALWAYS Do (nt) - Jim McShane 09:19:31 07/31/12 (0)

Follow Ups

RE: 4 pole caps in a voltage doubler circuit - Gingertube 21:05:05 07/30/12 (1)

thank you for the info (nt) - DAK 01:41:38 07/31/12 (0)

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