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Old 2nd Aug 2018, 8:59 am   #4
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default Re: Vibrators Solid State Replacements

That doesn't seem right to me!

The 'dead time' with a mechanical vibrator, allows the transformer's primary inductance to gracefully resonate with a capacitor across the primary, so that by the time the vibrator's 'new' contacts have made, the voltage across them is already very low because a half-cycle of oscillation has taken place. So they join with minimal sparking. When the contacts separate, there is also minimal sparking because the primary capacitor prevents a sudden rise of voltage as they separate.

Replacing the vibrator with a solid-state version, the 'drop-in' replacement would ideally have a similar dead time. Switch-mode power supply IC's such as the SG3524 are easy to set up to provide suitable drive waveforms - the obvious thing is a preset pot, tweakable while 'scoping the transformer waveforms, so that the ideal condition is attained.

If the dead-time is nearly zero, then the time for half a cycle of free oscillation is reduced. So to get nearly lossless switching, the commutation capacitance has to be REDUCED, not increased.

Reducing the commutation capacitance has the unwanted side effect that spikes due to leakage inductance will be larger. (But this is a separate thing to consider).
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