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Mosfets switching AC

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Bazza175

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Hi.
I am trying to switch ac for use in reverse phase dimming.

I would like to use 2 mosfets with thw sources and gates connected together.

My problem is switching the gate.
My setup currently is as follows.
I have a 12v source from a power supply that is regulated down to 3.3v for the electronics.
The output from the PIC has a opto coupler connected.

What i was thinking was to put the 12v supply on the output of the optocoupler so as to switch the gates of the mosfets. The sources from the mosfets would then go to 0v.

My conceen is that i dont know for sure if this is going to work safely. If at all.

Can anyone give me any pointers.

Oh appologies for the lack of a schematic im using my phone.
 
...

Oh appologies for the lack of a schematic im using my phone.

And I thought those phones did everything ;)

Why dont you use an opto-triac? Or an SSR?
 
I dont want to use triacs as i want to use reverse phase dimming. Triacs dont allow for this.
SSRs tend to be very big. Dual mosfets essentially create a SSR. Only thing is missing the switching aspect.
 
I have just connected up 2 mosfets like in the link.

**broken link removed**

When i put the mains on the drain pins with a load in series the load which is a 60w bulb gradually comes on until it is around 50% lit. It would suggest that one of the diodes are conducting in reverse or the mosfet is being activated.

At present there is no gnd or control signal connected.

Mosfets im using is irf830.

Any idea why this is happening.
 
You can't leave the gate floating, there will be leakage current and EM interference charging the gate. Use a 10k resistor between 0V and gates to prevent this.

Hope you are using isolation transformer and do things safely, because it seems you don't have enough experience to be playing with mains voltage.
 
I have plenty of experience with mains voltage. I just dont have experience with mosfets and mains voltages.
There is no isolation transformer hence the reason for the optocoupler providing isolation.

I have a 10k resistor in place from the gate to 0v already. When i said the signal was not connected i was referring to its connection to the PIC.
 
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