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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: PSU ripple current
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Date: Mon, 13 Jan 2003 11:15:06 -0000
NNTP-Posting-Date: Mon, 13 Jan 2003 11:15:07 GMT
Robert Strand wrote:
> 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).
How about i=C.dv/dt....
> If you can estimate the average DC voltage across the cap then the
> peak current is approximately (Vin_pk - Vdiodes - VDCav) / Rtotal.
Depends on what is dominating the current.
> If you can quantify all the necessary parameters it's simpler just to
> plug it into pspice.
No. Its simpler to plug it into SuperSpice:-)
Indeed, this will show some interesting results. Some runs of a simple
full wave bridge:
With R total (including diodes) = 0.02, Ipk=4.2A
With R total (including diodes) = 1, Ipk=4A
Only for large capacitors will the series resistance dominate.
Actually, its surprisingly messy to analyse a simple circuit like this
by hand. Of course, there is no reason to ever do this.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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