Drive a relay with PIC micro using a high side n-channel MOSFET

Thread Starter

roxi60

Joined Sep 2, 2018
67
Hello.
I would like to drive a relay 12 V, with a pic micro 0-3.3V, using a N-channel high side mosfet.
I tried different values of R and put NPN transistor but I couldn't manage, since I can not find a solution to have a switching voltage on gate that is higher (I guess) then +V, in order to switch on and off the mosfet.

Any suggestion or example circuit will be very appreciated.

Many thanks
 

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LesJones

Joined Jan 8, 2017
2,726
You will need the drive signal to go about 10 volts positive of you positive supply rail. If you use a logic level device about 5 volts above the + supply rail would work. Why do you want to use an N channel mosfet AND have the load on the low side ?

Les.
 

bertus

Joined Apr 5, 2008
20,863
Hello,

To drive a high side N gate mosfet, the gate voltage needs to be over the supply voltage of the circuit.
The circuit you posted witll not do this.
There are special high side drivers with a boost circuit to provide the higher voltage for the gate.
Here is one of the many examples:
https://www.analog.com/en/products/lt1910.html

Bertus
 

Thread Starter

roxi60

Joined Sep 2, 2018
67
Many thanks for your replies.
I would like to use this because I burned a high side P channel mosfet and I have now only n-channel mosfet, and I don't want to change the circuit, if possible.
Thank you.
 

LesJones

Joined Jan 8, 2017
2,726
It is not possible without changing the circuit. Even if you use a P channel device the drive signal must have a high level close to the supply voltage to switch it OFF.

Les.
 

Thread Starter

roxi60

Joined Sep 2, 2018
67
Thank Les.

I found in the forum such a circuit, but I don't think it is correct isn't it?Capture example driving a relay with high side nmosfet.PNG Anyway, I will change the circuit or the mosfet type.

Thank you.
 

ericgibbs

Joined Jan 29, 2010
11,073
hi,
When using NMOS I try to place the load in the Drain circuit, ie: low side drive.
It makes the circuit simpler and keeps the logic sense as Ard pin Hi = MOS On.
E
 

dendad

Joined Feb 20, 2016
3,610
I made a Hula Hoop that has addressable LEDs in it. It is driven by an Arduino Mini. To turn it on, a push button shorts out an N channel FET on the high side. When the Arduino starts up, a 50% PWM signal generates the high side FET gate drive voltage via a diode/capacitor voltage multiplier. The number of stages in the multiplier needed depends on the processor volts and the needed gate volts. This works pretty well, but is only good for on/off control, not if you want to PWM the FET.
 

ScottWang

Joined Aug 23, 2012
6,953
There are some ways that you can pick one you like.
1. A low Vgs as 2.5V N ch MOSFET.

2. One stage NPN bjt on low side → P ch MOSFET

3. One stage NPN bjt on low side → one stage PNP bjt on high side → N ch MOSFET (Vgs±10V)

SQ2310ES -- Nch, 20V/6A, Vgs=4.5V/30mΩ, Vgs=2.5V/34mΩ, Vgs=1.5V/42mΩ.
Si2300DS -- Nch, 30V/3.6A, Vgs=4.5V/68mΩ, Vgs=2.5V/85mΩ.
 
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