Oscilloscope first measurement

Measuring voltage spikes

New and old PSU

I have an old analog power supply unit (PSU) and two new ones (see picture to the right).

I thought I’d try to capture what happens with the voltage of one of the new PSU’s when I switch of the old analog one. So I switched the PSU’s on, hooked up the new one to the scope, set up the triggers in the scope, and switched the old PSU off…

WOW, that surprised me! As can be seen in the pictures below, the voltage spike when that old transformer is switched off is ginormous!

 

The length of this spike was not all that bad, only less then ½ a millisecond:

Switching off spike length

 

Spike voltage of 22.2 Volts!

But then there’s the voltage spike of 22.2 Volts Peak to Peak!

In a different PSU mind you!

Switching off spike voltage

 

Lesson:

What do we take away from this? Always disconnect all electronic experiments on the workbench before switching off (especially old) Power Supply Units!

 

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Oscilloscope first measurement