From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: PSU ripple current
Date: Wed, 15 Jan 2003 09:16:41 -0500
NNTP-Posting-Date: Wed, 15 Jan 2003 09:16:08 EST
Organization: Bell Sympatico
John Woodgate wrote:
> I read in sci.electronics.design that Mike Monett
> wrote (in <3E24D301.2A73@sneakemail.com>)
> about 'PSU ripple current', on Tue, 14 Jan 2003:
> >I just put this in SPICE. The ripple current is similar to a half sine
> >wave followed by a flat discharge. The shape of the half sine changes
> >with any change to the circuit, including leakage inductance of the
> >transformer, source resistance, load current, and of course, cap value.
> You can get different shapes depending on the ripple amplitude. SPICE
> allows you to explore all these possibilities
> >Although the charge current can change shape dramatically, it never
> >resembles a square wave, or even comes close.
> It does if the ripple amplitude is small - less than 5% of the d.c.
> output voltage.
Nope. I tried that also. It becomes closer to a perfect half sine wave.
> The charging voltage waveform is the tip of a (approximate, but very
> close if there is little leakage inductance in the transformer) sine
> wave of much higher frequency than the supply: you can see this if you
> display the ripple voltage and the diode current simultaneously. For
> very short charging times ( = small ripple voltage), this tip is close
> to a straight line. The discharge waveform is exponential, but again,
> for small ripple voltages it is nearly linear.
> Regards, John Woodgate
And none of these waveforms look like a square wave used in the previous