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electronic switch with Optocoupler and IRF350 Mosfet

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romel_emperado

New Member
hi,,how do i connect properly the optocoupler with IRF350 mosfets that would control an 8Amps, 220v Ac Motor??
my problem is i dont know how to properly connect the optocoupler to the gate of the IRF350 mosfet..

pls post any schematics that would help me...

thanks n advance...
 

MikeMl

Well-Known Member
Most Helpful Member
Is the circuit just a replacement for an AC relay, or are you trying to vary the speed of the motor by chopping the AC waveform? The answer has to do with how fast, and how often the mosfet is turned on/off?

Are you aware that there are commercial products called SSR (solid-state-relay) that are specifically made for this task?
 
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romel_emperado

New Member
yes this is just a replacement of ac relay..
the only function of this circuit is only to turn on and of the motor..
how often?? the answer is hours or even days...

i need some schematic to completely connect the optocoupler with the gate of the mosfet..tnx

i got here a diagram but i doubted a 15v with 1k resistor is conneted to the output of optocoupler.. is this ok to connect 15v to the output??
 

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mneary

New Member
A MOSFET is not normally used for this function. Is this a requirement?

Look at Solid State Relays. Here's a link: Digi-Key Part Search. Look for D2425-10. Note I'm suggesting a 25A 240V relay for a good safety margin.
 
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romel_emperado

New Member
A MOSFET is not normally used for this function. Is this a requirement?

Look at Solid State Relays. Here's a link: Digi-Key Part Search. Look for D2425-10. Note I'm suggesting a 25A 240V relay for a good safety margin.
yes, this is a requirment. the instruction that i got is i am going to use a optocoupler then a mosfet for a Ac motor with 8amps current rating...
is this possible??
 

MikeMl

Well-Known Member
Most Helpful Member
yes, this is a requirment. the instruction that i got is i am going to use a optocoupler then a mosfet for a Ac motor with 8amps current rating...
is this possible??
It is a hell of a lot of work, and possible failed attempts, to avoid buying a $40 ready-made solution. SSRs are a proven technology. You will spend days trying to make one that works as well as a readily available SSR.
 

marcbarker

New Member
SSRs are a proven technology. You will spend days trying to make one that works as well as a readily available SSR.
I second that. The SSR gives you so much, full isolation from the line with approvals, and operated with less than 20 mA.

Inside an ssr is the optocoupler, the triac (not mosfet) and its firing circuit. If an 'ssr' had no choice but use a mosfet, it would have a bridge rectifier included.
 
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romel_emperado

New Member
do u mean i need to have a bridge type rectifier connected in the mosfet to make it DC so that the mosfet woks??

does an AC Motor works with
DC??
 

RCinFLA

Well-Known Member
A single MOSFET will not work as there is a body diode that will conduct on reverse cycle. It is possible with to series P-Ch, N-Ch MOSFET's but drive circuitry is complicated.

Stick with Triac's with opto-isolator diac trigger.

If the motor has brushes (like power drill) it will run on DC.
 

romel_emperado

New Member
i think motors used in the industrial conveyor is a brush type motor so i may be run it using DC...

this is a requirement for me to use mosfet but if i would decide for my own i would stick to TRiacs and relays..
 

kchriste

New Member
Forum Supporter
If you are really hung up on using a FET to control AC, here is one way to do it:

Note that you'll have to use an isolated gate drive circuit such as a small transformer to supply the gate voltage.
As mentioned, a TRIAC and a TRIAC OPTO are the proper devices to use for this purpose.
 

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romel_emperado

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thnks kchriste i already have the optocoupling circuit. your schematic is a great help to me.. i would try this one..thanks...
the only thing that i would try to check out is what type of motor that i am using...
 

romel_emperado

New Member
thnks kchriste i already have the optocoupling circuit. your schematic is a great help to me.. i would try this one..thanks...
the only thing that i would try to check out is what type of motor that i am using...
 

mneary

New Member
If the obsolete IRF350 MOSFETs are cheap, (they should be), you can reduce losses to almost nothing by eliminating the diode bridge and connecting two MOSFETs in series, source to source and gate to gate. Use the two drains as your switch terminals.

Drive the gate as you would normally, with the sources as common.
 
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marcbarker

New Member
220Vac...

Im trying to use mosfet as switching device in ac just like the triac and relays does.
Just thought I ought to ask just in case it was DC supply you had. Because if you did that would change almost everything that's been said here!
 

romel_emperado

New Member
i posted an atachement. pls. evaluate this circuit if you think this would possibly work before i may buy this components..just to be sure a little.
 

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mneary

New Member
Your 5V, 15V and Ground to the right of the 6N137 must be isolated from the logic circuit and Earth and people, etc.
 

romel_emperado

New Member
how about this one?? which is much better of my two circuits??
never mind the two 2n series transistors 'coz that is not final just see if that design would trigger the mosfet..
 

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