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I'd like some input on whether or not to use a mechanical relay or some form of SCR setup to change the capacitance in my LC circuit that is currently operating at around 170V, 1A at 150kHz. (Not 220V, as the circuit shows)

Power is fused, isolated, rectified and sent through an H-bridge to the LC circuit from a Variac.

I thought of a design like this;

Capacitance switch

However, I think the opto-isolator should be on the MT2 side, not the M1 side. I may be wrong in that regard, but whatever; the main point being, I would like to put 3 of these capacitors in parallel and 'switch' them into the LC configuration separately.

Will this kind of design work, or am I better off using something like the aforementioned back-to-back SCR configuration, back-to-back MOSFET/IGBT configuration.

Please take into account the fact that I know very well this is quite possible using the correct relays, but it's more a question of whether or not this can be done using solid state parts.

EDIT: By the way, this is so I can tune what is essentially a Tesla coil digitally.

ARMATAV
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  • Personally, I'd look at using a pair of IGBTs back-to-back with a photo-voltaic opto driving the gates. Relays are a potential problem with the voltage rating and triacs are far too slow for 150 KHz. – Dwayne Reid Feb 27 '15 at 00:38
  • Thanks for the alternative, I was thinking of doing that (but with MOSFETs for easier control), however I was torn between doing back-to-back or full-wave rectifier configuration like mentioned here; http://electronics.stackexchange.com/questions/18858/equivalent-circuit-of-a-solid-state-relay/18861#18861 – ARMATAV Feb 27 '15 at 00:42
  • The problem with the bridge configuration is that the diodes introduce a discontinuity near each zero crossing. I do not know if that will have any effect but it is there. – Dwayne Reid Feb 27 '15 at 02:18
  • Ah, I see. Alright, I'll try your method for switching then. Thanks! – ARMATAV Feb 27 '15 at 02:31

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I would use a thyristor in place of a spark gap. Though you would have to manually tune it.but for auto tuning you will need pll or self oscillating circuit, or some sort of feed back.be just like oltc tesla coil. other wise your circuit will get a whole lot more complicated, which sounds like what you don't want if your considering relays.

neal kennedy
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