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From: "Klaus Vestergaard Kragelund"
Subject: Re: buck switcher problem
Date: Thu, 12 Dec 2002 11:40:30 -0500
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Organization: TDC Internet
"Frithiof Andreas Jensen" wrote
in message news:firstname.lastname@example.org...
> "Jeff" wrote in message
> > The surprising thing is
> > that the power supply caps are getting hot.
> That's, in a sense Normal, problem is when they get too hot...
> > They suggest doubling or tripling the caps or using tantalums
> > that are rated for the higher frequency.
> Bad Advice: You would be better off splitting the present one or two big
> cans you presumably use into a larger number of smaller devices. This
> lower the combined ESR and the thermal resistance.
The ESR won't change much. When you split it into smaller cans - the
individual cans will have higher ESR and the resulting ESR won't be much
better than with one large can. However your dissipation will be divided
between more cans which will let them run cooler because the power
dissipated in one can is related to I^2xR
If however you use more big cans - this will lower the ESR according to the
number of cans.
> Look at what the data sheets say - there are curves of permissible ripple
> current vs. frequency - then calculate how many you need to be within
> Also you should confirm that the capacitors you use now are really
> for high frequency/low ESR and not some thrashy 50 Hz consumer component.
> Panasonic make *both* types f.ex.
> Tatalums have additional problems, apart form the price: The ESR can get
> low that they will readily resonate with the PCB leads. This usually
> in a decent "Ka-Boom" when the capacitor subsequently overheats.
> > Any other advice? Is it ok to use aluminum electrolytic at this
> Should be, IF the capacitors are designed for switchers and lots of
> devices are used to make up the capacitance. Look at a Pentium/Athlon
> high-end motherboard for inspiration ;-)
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