Transistor switching higher voltage

[Mounter]

Hi guys

Here is an unusual question I need you to help me with.

Is it possible to switch say 230 V with a transistor (say mosfet) using 12 V?

Suppose the transistor spec says the maximum source drain voltage is 400 V and maximum source drain current at 10 V is 10 A. The gate threshold is 3 V. Closing time delay (drain source) is some 20 ps.

Now, the other question is: will it work if the "Source" ultimately connects to the Gnd of the 230 V source and not the Gnd of the 12 V source?

Essentially something like this:

View attachment 62607

Yes it is a 230 VAC source but it's rectified so no problem, right?

Edit: I should have drawn the diod after the mosfet, sorry my bad.

 

[ronsimpson]

I don't see a problem. You know the 12 volts is from Gare to Source of the MOSFET.

 

[Mounter]

Ok...

The reason I'm asking is this:

View attachment 62619

The application needs 12VDC, but it's only needed ON rarely, when it's not use I don't want the Switcher to be working needlessly.
Also, I want the whole system to turn OFF automatically (extravagancy to spare me the effort of pulling a switch)

Explanation to the schematic:
Double NO switch is pressed closed. The AC/DC switcher starts working, and so does the system (not relevant here except for the 555 timer module). 12 VDC is provided to the Trigger of the 555 IC timer module. 5 minute countdown. P3 is the Output of the 555 IC. All the mosfet gates are connected to this pin.

The mosfet gates are now closed (?). When you release the button switch 230VAC is alternately cycled through the two pairs of mosfets to the AC/DC switcher, until the timer runs out.

(Now the 555 IC is triggered LO. The timer module has to be powered up before the trigger turns HI. I'm not sure how to solve this either, any ideas? Maybe if the press switch was a triple NO I could wire the trigger pin through it to the solid GND? )

What I need help with:
Will the 50 Hz affect the transistors somehow badly?
What happens to a Switcher if the switch is pressed multiple times quickly? I guess there would be a time lag before the transistors eventually close. Pressing the button would probably be like igniting an engine, you need to hold it pressed for a second.
How can I solve the IC trigger issue?
Any other reason why this shouldn't work?

Here is a suggested N-type mosfet that almost matches the criteria (?):
https://www.electro-tech-online.com/custompdfs/2012/03/162657-da-01-en-IRFP_450_A.pdf

 

[tcmtech]

It would probably be far simpler and more reliable to just use an off the shelf solid state relay instead of the set up you are proposing now for the AC side switching system.

 

[Mounter]

Yeah I thought about that and sure it would be easier, one doble closing relay... Just thought that it would be more stylish with silent transistors. But then, it doesn't solve the timer reseting issue. And I'd still wish for someone knowledgeable to evaluate this concept in case it might work.

(If it's about the transistor clicking, isn't there a way to sound isolate them?)

 

[Diver300]

You only need to turn off one of the AC wires.

The problem that you have is that you need around 10 V between the gate and the source of each MOSFET to turn them on, and around 0V for them to turn off. The maximum gate-source voltage is +/- 20 V. The circuit has all the different MOSFET gates at different voltages, so your drive circuit would need to be really complicated.

That is why I would pay for a solid-state relay, which is basically what you are trying to do, but where someone else has done all the drive circuits and put it in a box for you.

 

[tcmtech]

Yeah I thought about that and sure it would be easier, one doble closing relay... Just thought that it would be more stylish with silent transistors. But then, it doesn't solve the timer reseting issue. And I'd still wish for someone knowledgeable to evaluate this concept in case it might work.

(If it's about the transistor clicking, isn't there a way to sound isolate them?)

Huh?

 

[Mounter]

Huh?

Huh?? Aha. ..[embarrassed]..
Whoops I didn't realize that a solid state relay isn't the same as normal relay until now. Thanks for telling me about it, definitely gonna use it here instead.

Are solid state relays more reliable than normal relays in the long run?

And lastly: any bright ideas on how to solve the timer reset issue?

 

[Reloadron]

I would use as tcmtech suggest a SSR. I would also place a snubber circuit across the SSR as outlined in this link. That should cure the resets if simply after going to an SSR they persist.

Ron