"Meindert Sprang" wrote in message ...
"Larry W4CSC" wrote in message
...
Yes, it may blow the rectifier diodes. A square wave is just switched
DC. A gasoline engine's battery powered ignition system works the
same way. The switching transistors come on, DWELL for the pulse
width, then switch off, like the points opening.

big snip

Sorry Larry, your explanation is way off. The inverter, being a square wave
one, doe not produce spikes like an ignition system. Also, the squarewave
does not produce induction spikes in the connected adaptor. The only reason
why the rectifier in the adaptor might fail from the rapid reverse of the
square wave is the fact that it takes time for a diode to block when the
voltage is reversed. With a sinewave gradually changing polarity, there is
no problem. But with a square wave, the polarity is changed very rapidly.
This causes all diodes in the bridge to conduct for a very short time ( a
few microseconds) effectively shorting the inverter output during this time.
This produces high current spikes which can be audible.

The sound the OP heard from his razor whn switched off, probably comes from
the input filter capacitors in the razor, that also conduct during the phase
change in the square wave.

Meindert

If the output of a square wave inverter is connected directly to a
line transformer (i.e. wall adapter), then Larry is exactly right.
You can verify this with a simple experiment: connect the output of a
function generator to the primary of a small 60 Hz transformer, and
then connect one channel of a scope to the primary of the transformer
and the other channel of the scope to the secondary. Set the function
generator for a 60 Hz sinewave, and you will see sinewaves across both
the primary and secondary windings of the transformer. Now, switch
the function generator to a squarewave output, and you will see a
large voltage spike at each edge of the squarewaves. The spikes will
alternate between positive and negative.

MJM