Power conditioners and smpsu

[pucho812]

Can’t seem to find this answer or maybe I am looking in the wrong spots but

If a power conditioner is outputting something other then a sine wave it seems to reduce lifespan of smpsu.

I have seen in the past things like the monster 3500 power conditioner outputting a square wave which seems to kill smpsu’s rather quickly.

Why?

 

[ccaudle]

Without looking at the circuit details my first guess would be that the square wave output causes something in the power factor correction circuit to overload. The PFC measures the input voltage, and tries to make the output current of the PFC stage follow the input voltage, so that the combination causes the input impedance to appear roughly resistive and lower distortion than a typical diode into bulk capacitor input stage. Normally the output of the PFC would be pulsing on and off so that on average the current follows the input voltage, but at any instant it is either completely on or completely off. If the input voltage jumps up and stays high, the output driver has to stay on for much longer than usual, so perhaps the output inductor saturates, which then causes an overcurrent in the output driver. Or perhaps the high duty cycle causes the PFC output to go over voltage.

So my guess is that the problem is with the PFC, because the rest of the AC-DC SMPS is just a high voltage DC buck converter, and that would not have any problem with square wave input.