High side Mosfet driver using n-channel

Thread Starter

jonfarrugia

Joined Feb 19, 2010
71
I've been looking at different ways to control an N-channel mosfet as a high side switch for a 12VDC load.
The signal to the circuit will be from an arduino it may or may not be a pwm output.
I was considering using an LM2941CT set for 20vdc as the power for the MOSFET gate driver circuit.

If I connect the arduino output to a transistor that controls either 20vdc or 0vdc to the high-side n-channel MOSFET gate, would this be ok? See attachment

I was going to use this regulator because I want to use it's power to drive 20 MOSFET gates from 20 different Arduino Outputs.
 

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#12

Joined Nov 30, 2010
18,159
That looks right, give or take frequency related parts. Depends on how fast you want to run it.
 

THE_RB

Joined Feb 11, 2008
5,438
There are a heap of specialist small ICs called "high side FET drivers".

Many of them even generate the higher voltage needed for the gate, so you don't need dual PSUs. :)
 

#12

Joined Nov 30, 2010
18,159
As the gate is passing 12 volts, going positive, there is 8 volts across the 10K resistor. That's .0008 amps. The gate is 190 pf. The gate voltage will be moving at 4.2 volts per microsecond if I did the math right. The half wave time of 5kHz is 100 usec. That says more than 2% of the 5Khz time will be spent in the last 8 volts.

I think, speed it up a bit. 750 ohms for R1

Still, RB has a better idea.
 

Thread Starter

jonfarrugia

Joined Feb 19, 2010
71
There are a heap of specialist small ICs called "high side FET drivers".

Many of them even generate the higher voltage needed for the gate, so you don't need dual PSUs. :)
Can u provide a link to a single ic driver that might work in this application?
 

Thread Starter

jonfarrugia

Joined Feb 19, 2010
71
As the gate is passing 12 volts, going positive, there is 8 volts across the 10K resistor. That's .0008 amps. The gate is 190 pf. The gate voltage will be moving at 4.2 volts per microsecond if I did the math right. The half wave time of 5kHz is 100 usec. That says more than 2% of the 5Khz time will be spent in the last 8 volts.

I think, speed it up a bit. 750 ohms for R1

Still, RB has a better idea.
Thanks. I'll test this when the components come in.
 

MikeML

Joined Oct 2, 2009
5,444
Why not just use a PFet preceeded with an NPN? That also eliminates the need for a higher than 12V power supply or charge pump.
 

#12

Joined Nov 30, 2010
18,159
Or move the N-fet to the other side of the load.

There are 6 ways to do this. Why you choose the most difficult?
 

Thread Starter

jonfarrugia

Joined Feb 19, 2010
71
I need high side switching for this application.

I went with the above circuit cause I have the IRF510 MOSFET in stock.
 

#12

Joined Nov 30, 2010
18,159
That pretty much confirms my math. The MikeML circuit has 3usec time one way and 8 usec time the other way. That demonstrates that a 10K drive resistor is going to be awful in this application.
 
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