Driving MOSFET gate using dsPIC33

I would like to drive a MOSFET gate using Mc (3.3V) to switch another 3.3V for the Accelerator by using N-Chanel logic level MOSFAT.
IS it possible?
Can i Use it as high side drive or it should be low side drive?


Please Advise

If you have a mosfet with low enough threshold you can use it as a low side driver. You're going to have to read some data sheets.

Hi,

Designing a circuit means you need specifications first:
* hat is the max load current
* what's the desired max voltage drop at the Mosfet

Btw: I like the idea, that GND is the common reference point for all connected systems.
But if you switch the GND, other systems can't refer to it, therefore I recommend to switch high side power supply line.
The easiest way is to use a P-ch Mosfet.
If you need some protection (overcurrent...): there are ready to buy power supply switches.

Klaus

Btw,you can't use an N-channel mosfet as a high side driver the way you're showing it. The gate voltage has to be higher than the source voltage for it to turn on.

barry said:

Btw,you can't use an N-channel mosfet as a high side driver the way you're showing it. The gate voltage has to be higher than the source voltage for it to turn on.

Click to expand...

Thanks all for your reply. Thanks Barry. May i ask why Gate Voltage must be higher then the Source to turn ON? any explanation
one more thing, for safety purpose on N-Channel low side, do i need to use a resistor between the Gate and the Drain?

KlausST said:

Hi,

Designing a circuit means you need specifications first:
* hat is the max load current
* what's the desired max voltage drop at the Mosfet

Btw: I like the idea, that GND is the common reference point for all connected systems.
But if you switch the GND, other systems can't refer to it, therefore I recommend to switch high side power supply line.
The easiest way is to use a P-ch Mosfet.
If you need some protection (overcurrent...): there are ready to buy power supply switches.

Klaus

Click to expand...

Thanks KlusST,
As i mention on the Picture, the voltage source is just 3.3V and i need min 3V at the Drain as an output. the Load Current is not more than 50mA.
My concern is if i use P-Channel as high side, does it work

Hi,

May i ask why Gate Voltage must be higher then the Source to turn ON? any explanation

Click to expand...

Please read through basic Mosfet circuits, it's operation and it's voltages.

Look into any N-ch datasheet. There you find the condition how to turn ON the mosfet. It is V_gs....it needs to be higher than lets say 3V.
V_GS means: Voltage from gate to source.
So if the voltage from gate to sour e is 3V and the source to GND voltage is 3.3V .... it should be obvious, that the gate (gare to GND) voltage needs to be 6.3V.

********
P_CH:
Let's take something like FDV304P (just as example. There are many others that maybe better fit your needs)
It's ON resistance is 1.5 Ohms at V_gs = -2.7V.
You can expect a voltage drop of less than 1.5 Ohms x 50mA = 75mV.

Klaus