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From: Robert Strand
Subject: Re: PSU ripple current
Date: Mon, 13 Jan 2003 18:19:53 +1100
Organization: ihug ( New Zealand )
NNTP-Posting-Date: Mon, 13 Jan 2003 07:22:42 +0000 (UTC)
User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
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steve c l wrote:
> Given the full wave ripple voltage across the input capacitor of a psu,
> how does one estimate the ripple current in the capacitor. If the ESR is
> the main determining element, are there typical values of this that can
> be used in the estimate? Some guidance would be appreciated. BTW the
> ripple frequency is 100 hertz. and the capacitor is say, aluminium foil
> 5000mfd steve
It depends not only on the cap ESR but also on the transformer winding
resistance (secondary + primary reflected into the primary).
If you can estimate the average DC voltage across the cap then the peak
current is approximately (Vin_pk - Vdiodes - VDCav) / Rtotal.
If you can quantify all the necessary parameters it's simpler just to plug
it into pspice.
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