Hey from sydney Australia

I need a schematic of a way of switching mains from a sine wave to a square wave. Keeping it simple. I think it would just involve a few SCRs and diodes

by fiero128
July 04, 2013

You need to define your requirement a lot more clearly.

Is this to provide a low power logic level signal from the mains?

Is it to provide a high power signal from the mains?

What load do you require to drive?

What short circuit protection (fuse, current limit, foldback etc.)?

What mains frequency?

What mains voltage?

What current?

What load power?

What load impedance?

Does the output have to be at the same frequency as the mains input?

Plus this whole area comes with the usual warnings about this being mains, unless you are absolutely certain that you know what you are doing: don't.

by signality
July 05, 2013

Is this to provide a low power logic level signal from the mains? No, to use 240Vac directly

Is it to provide a high power signal from the mains? Yes

What load do you require to drive? 6 to 8 amps

What short circuit protection (fuse, current limit, foldback etc.)? circuit breaker

What mains frequency? 50 Hz , like all the mains here in Australia

What mains voltage? 240 VAC

What current? 6 to 8 amps

What load power? 15 to 20 watts

What load impedance? Unsure yet1 Kohm

Does the output have to be at the same frequency as the mains input? No, the aim is around 42.2 Khz. The aim is to get as close but not fussy

Plus this whole area comes with the usual warnings about this being mains, unless you are absolutely certain that you know what you are doing. I plan in using a variac to start low mains voltage and make the alterations needed to increase to 240 v AC

by fiero128
July 05, 2013

"What load do you require to drive? 6 to 8 amps"

Into what?

A resistor?

A motor?

A Marx Bank?

Cane Toads?

"Does the output have to be at the same frequency as the mains input? No, the aim is around 42.2 Khz. The aim is to get as close but not fussy"

So you want to convert AC mains into a 42.2kHz squarewave capable of driving a 8A into a load of around 1k.

That's an output voltage swing of 8kV.

That's a load power of 64kW.

I think you need to go away and do some basic arithmetic.

:)

"I plan in using a variac to start low mains voltage and make the alterations needed to increase to 240 v AC"

Beware that a Variac is not isolated:

https://en.wikipedia.org/wiki/Autotransformer

You should at least connect to that through a high power 1:1 isolation transformer.

From your very own power station.

by signality
July 05, 2013

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