Switching wall-wart noise

How much noise should I expect from a 5 volt 800mA, switching, regulated wall-wart?

The wall-wart is powering a PIC processor and some other logic and works well when plugged into a surge protected power strip, but causes erratic operation when plugged into a regular unprotected AC socket.

The processor inputs are driven with schmitt trigger inverters (74HC14) so I would expect the noise rejection to be about 2.5 volts. I can see about 150mV of noise on a 15mHZ scope, but apparently the noise level exceeds

2.5 volts that I can't see.

I added a 1 ohm resistor in series with the +5 and a 0.1uF cap from other side of resistor to ground which seems to cure the problem but I don't see much change in noise level on the scope.

The load is 300mA, so what would be an optimum RC filter to use? Or should I replace the wall-wart?


Reply to
Bill Bowden
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I would replace it. I use the Elpac WM series of linear regulated wallmounts. I use them to power custom test equipment used to measure noise, so you know they have to be quiet. Digi-Key & Mouser carry them.

Steve J. Noll | Ventura California | | The Used High-Tech Equipment Dealer Directory |

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Reply to
Steve J. Noll

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