Using a mosfet like a relay

Thread Starter

MikeJacobs

Joined Dec 7, 2019
94
Quick question for you guys.
I cant find a suitable SSR for what I want to do because of the voltage drop.
Many of the relays im looking at have a 1.5 V drop or greater and I cant have that.
So im looking to replace my relay with a mosfet.

What are the disadvantages to this? I know I can get fets with very low RDS so the voltage drop will be low and power dissipation also low.

On occasion the source voltage will shut off and the gate would reamin (closed / on) then the voltage at the source may turn back on. This is just a function to the circuit. Does anyone see any issues with this? Thanks
 

ericgibbs

Joined Jan 29, 2010
9,117
hi Mike,
Welcome to AAC,
What sort of voltages and currents do you have in mind.?
What is the driving source.?
Load type.?
E
 

Alec_t

Joined Sep 17, 2013
10,611
On occasion the source voltage will shut off and the gate would reamin (closed / on) then the voltage at the source may turn back on.
Not clear what's going on there. If you're keeping the gate voltage constant but switching the source voltage to turn the FET on/off then whatever is doing the switching will have to carry the full load current. Doesn't that make the FET redundant?
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
94
No, it just so happens that the signal through the turns off and on , on occasion.

Sometimes I want the on and off to allow through the fet other times I do not
 

ericgibbs

Joined Jan 29, 2010
9,117
hi M,
If the MOSFET Gate is kept enabled during a Power Off period, the MOSFET should start conduction as soon as the main power is restored.
E
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
94
hi M,
If the MOSFET Gate is kept enabled during a Power Off period, the MOSFET should start conduction as soon as the main power is restored.
E
Thanks

That is what I thought. I just wanted to make sure I was not forgetting something. So there should not be any issue with trying to run this like a SPST NO SSR Relay im guessing. Just don't want to miss something. Appreciate everyone's input
 
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