by erichayes » Sat Mar 06, 2004 9:00 pm
Hi All,
Back in the days when power switches actually contolled the mains, manufacturers almost always installed a .05~.1 uF cap across the switch to suppress turn-on transients (and extend switch life).
Now, with everything turned on by a microprocessor, there are virtually no power switches, other than the ones on power entry modules (PEM).
If you're planning to use a power switch other than a PEM to control the line voltage to your project, you should install the cap. Ceramic, rated at 600V minimum is best, if you can find them; otherwise a good poly film in series with a 75~100 ohm 1/2 watt resistor will help. The same would apply to standby switches, as long as they're handling AC, but then you'd definitely want to use a ceramic rated at 1KV or higher.
Also, if you're recapping an old amp, include this one along with the coupling caps. It was the major cause of switch failure.
Eric in the Jefferson State