can triacs rapidly switch AC into a transformer

[Zak28]

Can a triac thyristor chop standard AC mains into 1-20Khz to transformer step up voltage as higher frequency than standard mains frequency?

There might already be applications for this but Im not sure whether it can be used to step up voltage into higher frequency using transformer. This would suit a tesla coil much more efficiently than low voltage step up methods.

 

[KlausST]

Hi,

The biggest problem is that triacs, thyristors, SCRs can't be switched OFF like transistors.

Once they are triggered they stay ON until current goes to zero.

Klaus

 

[Zak28]

I thought light dimmers switched the current quicker than mains frequency.

Would there be a workable solution implace of thyristors to have the high frequency?

 

[Easy peasy]

forced commutation was used to turn off SCR's ( mainly ) and triacs - however a lot of extra circuitry is required - then along came mosfets & IGBT's so much easier to chop the mains or whatever, given that you can now easily buy 1200V SiC mosfets at > 50A SCR's & Triacs are seldom if ever used in modern times.

 

[Zak28]

forced commutation was used to turn off SCR's ( mainly ) and triacs - however a lot of extra circuitry is required - then along came mosfets & IGBT's so much easier to chop the mains or whatever, given that you can now easily buy 1200V SiC mosfets at > 50A SCR's & Triacs are seldom if ever used in modern times.

If this is the suggested MOSFET switch, what is gate driver lowside common to? Or there is a better MOSFET topology.

 

[FvM]

Gate driver should be of course referenced to common source node.

There are several reasons why the "chopper" circuit can't be used in the shown basic configuration:

- Mains input filter required to comply with EMC rules
- Switching inductive loads creates large overvoltage that kills the MOSFETs if not clamped approriately

 

[Easy peasy]

your approach is a little bit simplistic - you will need snubbers across the mosfet switch, and source referenced gate drive, you will get maximum power near the mains peaks ( 325Vpk for 230Vac )

Per your question about SCR's closing faster - inverter grade SCR's - hard to find now, could switch up to 20kHz if force commutated or in a resonant ckt - typically 0.3uS turn on time - a good idea to have a close read of a data sheet for a good SCR ... to see its limitations, hold current, latching current etc, turn on time ...

mosfets or IGBT's far easier to use.

 

[Zak28]

This seems far more simple and practical. It would need a ballast or other current limiting element. Do SMC rectifiers typically fail short or open?



There are tesla coil diagrams depicting several series 1kv slow rectifiers to prevent short circuit issues if diode is damaged. But fusing the circuit at power entry side should prevent any short circuit issue.

At mains voltage a snubber diode is fine over resistor capacitor. The only issue is neutral can be within several volts or less to gate turn on voltage. Is there a remedy for this?