On Thu, Jul 05, 2007 at 01:28:24AM -0400, DJ Delorie wrote: [...] > Both 3.3 and 5v work fine. I'm getting about 18mV P-P ripple on the > 3.3v line, at about 150Khz (the switcher's freq) plus a smaller 6MHz > ripple, probably from the ATX power supply I'm using. Shorting the > 3uH output inductor has no affect.
Is that the secondary output inductor, after the first output inductor and capacitor? If so, I suspect that's because you don't have a secondary capacitor or any other load after the secondary inductor (not counting your scope, which I assume has very high input impedence and doesn't count as a load). If you don't allow an inductor to pass current, it will not allow a voltage to develop across its terminals, and so just looks like a conductor. Until you let it pass current by putting a load on it. V = L * dI/dt I = 0 => dI/dt = 0 => V = 0 Stick a capacitive load on there and you'll see a reduction in that ripple, I bet. (A resistive load would result in a much smaller reduction; possibly not even measurable.) _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
