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AC Switch using MOSFET

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hozefa

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Hello,

I need some guidance for designing AC switch using MOSFET. This will be controlled from Microcontroller (Switching Application).
For example I have 20 bulb as a AC load and at a time only one bulb should be ON, after some time AC voltage (230V AC) will be switched to the next Bulb and it goes on (like dancing light), and switching will be controlled by Microcontroller.

So the I/P will be 230v AC and out put also 230v AC, up to 5-7Amp.

Please give some suggestion on how to design this application using MOSFET and what all criteria has to keep in mind while designing this application.
 

pranam77

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A triac like BTA12/600 will be highly suitable to switch the said load driven with AC at 5-7 amps. Cheers
 

brunofunchas

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Re: How to design AC Switch using MOSFET

Hello,

You have to use a TRIAC instead of a MOSFET.

As an alternative you can use a PLC.

Best regards,
Bruno
 

    hozefa

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hozefa

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Thanks Bruno & pranam for the reply,

if you can guide me or give some reference circuit/schematic of how to use TRIAC for this application then it will be really help full for me to get start this project
 

pranam77

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This thread will give you more ideas about the ttopic. Cheers.
 

    hozefa

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hozefa

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Thanks Pranam,

I have checked that thread, it was useful, and that what I was looking for, SSR (using TRIAC) simple circuit to use in embedded System.

But when I have check the price of SSR it was around 20$ each (Single Load), too costly for my application where I need some 16 to 20 SSR (around 20 AC Loads).

Can anyone guide me in designing this application using TRIAC?
 

pranam77

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Yes naturally SSR's will be costlier. You can have more idea and a schematic from one of my old post in this link given below which describes how to drive an AC load with triac. Cheers
 

    hozefa

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gvnl

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You can command an opto-triac like MOC3020/3040 by the microcontroller (or similar), then the opto will drive a bigger triac (like BT138) connected to the load. This way, you maintain isolation. Schematics are provided in the datasheet of the MOC3020/40, so have a look.

Regards

Added after 1 minutes:
 

bobcat1

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HI

It is a bit complicated to use a MOSFET instead of TRIAC

Search EDN design Idea (at EDN site) there was once an application who show how to use MOSFET as AC switch

Also go to IR site and search for MOSFET application note - they have some application note who show's the use of MOSFET as an AC switch

All the best

Bobi

The microcontroller specialist
 

itaig

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If you don't need isolation then you can directly drive a sensitive gate triac using the I/O port on a micro through a resistor (about 100R will be ok).

You will need to connect the A1 terminals of the triacs together and the VSS of the micro should also connect to this point.

Connect the loads to terminal A2 of each triac.

Warning!! the micro will be at live voltages. You will need to isolate the mains before connecting to a programmer otherwise you project, programmer and PC may become a very expensive puff of smoke :D

Another thing is to remember to maintain clearance and creapage distances on your PCB.
 

hozefa

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Thanks Everyone.

Hey Pranam, that link was useful. I have got some idea that how to use TRIAC and for some extra protection I can use MOC3041/21.

I am planning to use SC141 TRIAC for my application, 6amp.

I will upload the schematic soon so you can just check it up if you have time.

- Does TRIAC need any delay while switching it ON/OFF?
- How fast I can do switching?

Thanks Once again.
 

pranam77

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hozefa said:
Does TRIAC need any delay while switching it ON/OFF?- How fast I can do switching? Thanks Once again.
It is my pleasure to have helped some one. The triac itself is a solid state form of an Electromagnetic relay. Thus no relays are again required. naturally you can switch faster than a relay with a triac. Anyways i'll wait for your schematic. Cheers
 

hozefa

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Hi,

Here is the schematic, have a look.
Please tell if any extra precaution is required in the circuit.
 

sahu

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hozefa said:
Hi,

Here is the schematic, have a look.
Please tell if any extra precaution is required in the circuit.
i think ,R6=100E , R3=3.3K & no req. R4=5K
 

pranam77

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hozefa said:
Hi, Here is the schematic, have a look.
Please tell if any extra precaution is required in the circuit.
I think it shud work fine. Only the snubber resisitor may be changed to 100E as "Sahu" mentioned. If you use BTA6/600 or BTA12/600 sieres triacs, these come with built in snubbers. Thus external circuits may be left off. Cheers
 

    hozefa

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hozefa

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Thanks Pranam for Help.

Once I built & test this, I will let you know.
 

hozefa

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Hello,

I have used TRIAC for AC switch but the requirement is of High Frequency AC Switching, which can be achieved by using MOSFET.

So can anyone help me in designing AC switch using MOSFET?
 

FvM

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The new requirement sounds confuse when reading your original post.
 

pranam77

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hozefa said:
Hello, I need some guidance for designing AC switch using MOSFET. This will be controlled from Microcontroller (Switching Application).
For example I have 20 bulb as a AC load and at a time only one bulb should be ON, after some time AC voltage (230V AC) will be switched to the next Bulb and it goes on (like dancing light), and switching will be controlled by Microcontroller.
So the I/P will be 230v AC and out put also 230v AC, up to 5-7Amp.
Please give some suggestion on how to design this application using MOSFET and what all criteria has to keep in mind while designing this application.
hozefa said:
Hello, I have used TRIAC for AC switch but the requirement is of High Frequency AC Switching, which can be achieved by using MOSFET. So can anyone help me in designing AC switch using MOSFET?
How come suddenly you are enlightened after all these questions and answers?
 
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    gamitm

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hozefa

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Hi Pranam,

This is totally new requirement I have. Using TRIAC, the old requirement was full filled.

I have posted the same query as new post also (as a new requirement).
In this new requirement I need high frequency switching.
 

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