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that means a immediate breakdown! You must install a protection circuit around your semiconductors
to protect them of those reverse voltages. Damping waves in high power system is
frequently causing lots of trouble, moreover when attention has not been paid for them!
5.­May I suggest the reader to try some experiments and generates such damped waves?
The capacitor may not be polarised. (voltage oscillating over and under zero volt).
It can be charged via an auxiliary DC power supply with a serial resistor to permit the charge
,but high enough to avoid any perturbation during the generation of the damping wave.
Usual low voltage can be used as charging voltage.
To display the wave, a memory scope can be connected at the capacitor. It will be selected as
single trace, triggered by the capacitor voltage itself.
A non­memory conventional scope can also be connected but you will probably design your
circuit for slow damping waves, or with a long persistence scope if any….
If you do those tests, you may have some problem with the shorting switch!! Conventional
switches have a usually a bounce of the mobile contact during the mechanical commutation. So
there are a few interruptions before the contact is really fully fixed. If the duration of that bounce
is close to the pseudo­period of the damping wave, you may see something like stroboscopic
effects! The display may be fully distorded!
The only correct way is to use a small mercury­wetted relay. Due to the capillarity, there is a
mercury bridge between the moving and fixed electrodes during the mechanical commutation of
the reed switch. There is no bouncing at all and the switching is perfect.
6.­ Note: For more complex calculations, see also into the book
“Reference data for radio engineers”
(published by Howard W. Sams & CO.,inc ITT)
73's from ON4BX