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From: John Woodgate
Subject: Re: buck switcher problem
Date: Wed, 11 Dec 2002 21:16:06 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Wed, 11 Dec 2002 21:30:28 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Boris Mohar wrote (in <firstname.lastname@example.org>)
about 'buck switcher problem', on Wed, 11 Dec 2002:
>On Wed, 11 Dec 2002 18:12:48 GMT, "Jeff" wrote:
>>I have a power supply using a switching regulator that is supplied by a full
>>wave bridge rectifier and a stepdown transformer. The surprising thing is
>>that the power supply caps are getting hot.
>>The values for capacitance and ripple current are all within the
>>calculations, but there is a large temperature rise on the caps. The
>>regulator vendor says it is a problem with the 300 kHz switching frequency
>>and aluminum electrolytic.
>>They suggest doubling or tripling the caps or using tantalums (expensive!)
>>that are rated for the higher frequency.
>>Any other advice? Is it ok to use aluminum electrolytic at this frequency?
> Try faster diodes.
Definitely fast diodes are necessary for 300 kHz. But also put 0.22 uF
polyester of appropriate voltage rating across each electrolytic filter
capacitor. At 300 kHz, anything larger may be near self-resonance,
depending on lead length. Keep the leads as short as possible..
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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