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Old 26th July 2008, 12:40 AM   #1
gary h is offline gary h  United States
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Default parallel capacitors in PS question

Hi all,

I recently got my plate supply component values using PSUD2. Some of the caps modelled are a bit expensive, bulk only, or not available at high enough voltage rating. The caps will see around 300V so I'm figuring a 450V minimum rating, right? And I'm going with electorlytics.

Some of the caps needed are: 0.68uF, 60uF, 200uF. I've tried searching Mouser, Digikey, Newark for 450V caps +/- 10% but keep coming to the conclusion that running pairs in parallel might be more suitable. For instance, 2 33uF to replace the 60uF.

What is the thinking on this? I read that I need resistors to ensure both caps share the load equally, how do I calculate and configure these? Does the 450 voltage remain unchanged ?

thanks,

gary
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Old 26th July 2008, 12:42 AM   #2
gary h is offline gary h  United States
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BTW,

here's the model
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File Type: jpg 300_b+.jpg (92.3 KB, 218 views)
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Old 26th July 2008, 01:31 AM   #3
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400V would do, but can't hurt going higher. I'd use a 800-1000V film cap for the first one, though. Actually you might want to get a range of valuse and adjust this cap for the final voltage.

Parallel caps don't need anything special - series caps usually call for equalizing resistors since they are generally used to get higher voltage ratings.
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Old 26th July 2008, 05:08 AM   #4
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Panasonic ED, TSED, TSHB from Digi-Key.  There are no better caps, as far as I am concerned, and I have A-B tested them with Black Gates (of which they are the equal), and Cerafines (to which they are superior).

Five clams each, delivery in five days.

Get to work,

Poinz
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Old 26th July 2008, 09:06 AM   #5
nitrate is offline nitrate  United Kingdom
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Hi there,

I've had the same problems lately. Had to resort to e-bay for my bigger caps ( 10,000 @ 100V min ). However for my high voltage B+ caps i re-claimed them from old switchmode power suplies. I got some nice 820uF @ 250V out of an old photocopier supply and some 330uF 400V out of an old AT computer PSU. However you may still struggle to find voltages as high as what your looking for. Seems there is no good source of cheap high voltage caps in the UK at the moment.

I've tried using caps in series in my main PSU but it was hard to balance the voltages and the ESR was so high that i still had high ripple. Also you have to remember that caps in series are like resistors in parallel, 1/C tot = 1/c1 + 1/c2 + 1/c3 ect. Thus if you put two caps in series to double the voltage you end up with only half the capacitance and double the resistance. Both these side effects make using caps in series, for me at least, not worth it. Just my opinion tho...

Leigh
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