I have a power supply (flyback) takes 28V DC in and output +/- 5V out. Load is about 1 watt.
The problem I'm having is that at specific temperatures, over a 0.5 C temperature band, the output gets noisy. Then as the temperature band passes, it cleans up to normal room temp levels. Between 25 and 125C I get three of these bands. One at 62C one at 80C and one at 97C. It is very repeatable with temperature but I can't figure out why it is doing it.
Any ideas?
On Tue, 08 Nov 2005 01:38:04 GMT, "Mook Johnson" wroth:
It's just marginally stable at all temperatures but less stable at a few. If you can increase the margin, the problem might go away.
Take a look at the feedback parameters. Assume it was noisy at all temps and persue the suggested remedies.
Is the design based on a particular IC? Post the circuit somewhere.
Jim
I have between 45 and 65 degrees of phase margin at all combinations of line and load. This was verified on the gain phase analyzer.
Stability doesn't seem to be an issue. There is something else going on.
Come sort of resonance occurring dur the magnetics changes that "tune" a circuit for high Q at those temps?
Just wondering if anyone had seen anything like this before.
Does it also move with input/output voltage ratio or output current?
What else is in the circuit or nearby?
Does it happen when the turn off time and the system clock or some such get in sync?
What flavor capacitors are you using in the feedback circuits? If they are ceramic what type.
Does it happen with a different inductor? Does pressing on the core make it stop?
Are the switching semiconductors oscillating during the turn on/off edges?
-- -- kensmith@rahul.net forging knowledge
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