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IRF5305S Power MOSFET, is switching voltages of 3V possible?

powersupplyfix

Jan 19, 2017
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Hi all,
found this interesting yyd-3 module which is some sord of four channel "silicon" relay.

It has four (817) optocouplers who's open collectors (Emitter:GND) drive (VCC:10M->G->10K:GND) the gate of an IRF5305S (used as a high side switch).

I looked at the datasheet of that P-FET but am unsure if it will switch reliably at VCC voltages down to 3V.
Those FETs need to switch minimum 100mA, at max 1.2A (all at 3V) and will operate at 70C temperatures.
They are used as relays, i.e. to power lights etc.

Has anybody worked with these FETs or does anybody know if there is a minimum (VCC) voltage or current required for these types of hexfets to switch on reliably?

Thanks!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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The Vgs(th) can be as high as 4V, and the device is specced for a minimum Vgs of 4.5V, so it would fall somewhere between "won't work" and "unreliable".
 

BobK

Jan 5, 2010
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The 3-20V spec for that module is the voltage to drive the LED in the optocoupler, not the gate drive for the MOSFET. The input must be through a resistor that will allow 5mA of current.

Bob
 

powersupplyfix

Jan 19, 2017
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Thank you for your replies.
Yes, this is regarding the FET, not the input to the optocoupler LED (which is driven by 12V).
The emitter/collector of that optocoupler transistor would pull down the 1M pull up at the gate of the FET.
On page 2, VGS seems specced (Threshold) from 2-4V, so 3.3V would fall in it's range of operation, right?
My question is about VDD (or VCC or VDS?), if that can be also at 3.3V, or does it need to be higher?
In that case, do you know a (drop in) FET which you could kindly recommend, and which could go lower, say to 2.5-3V @ 2A?

The stuff (LEDs lights, motors etc) which needs to be switched on/off is being powered by 3.3V only (but controlled via optocouplers by 12V).

It all works well with a relay version, but those 3.3V relays need 120mA each!

Thank you!!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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The important factor is where the voltage which is supplied to the gate of the MOSFET comes from.

In most optocoupled circuits, this would come from the load side.
 

powersupplyfix

Jan 19, 2017
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Yes, the voltage to the gate comes from the 3.3V power supply of the load side .
I'm not worried about the "LED" side of the optocoupler, as there are 12V available.

Question is if this HEXFET can switch [email protected]@70C reliably with a gate going from 0V to 3.3V, and it's source (being high side switch) connected to same 3.3V. And the load connected to the 0V.

Or if not, do you guys know a part? There are sooo many...

Thank you all for your input!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Remember that the optocoupler will not pass all the voltage to the gate (it will drop some). I would think that anything less than 5V would be problematic.

A MOSFET with a lower Vgs(th) might be able to be substituted.
 

BobK

Jan 5, 2010
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You may notice that the board is speced to switch a minimum of 5V. It will not likely work at 3.3V. The threshold voltage is listed at min 2 and max 4V. That is the voltage that allows 250uA to pass. So it is possible that it will not even allow 250uA of current at 3V let alone 2A.

Bob
 
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