Simple High Voltage mosfet driver circuit

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george fleming

Joined Dec 18, 2023
1
I need to drive a highside mosfet switch from a GPIO pin. The high voltage supply can be between 42.5V and 90V. I was searching around for the simplest solution I could find (small, low cost, few external components). I found a few options, but then cam up with this on my own:

1702912921815.png

I didn't find this particular type of example online, but it seems like the simplest way to achieve my desired functionality. Does anyone have feedback or ideas on what I might be missing or what to watch out for? I like the simplicity of this circuit because it is very easy to set the drive parameters:

GPIO = 0 to 3.3V
R2 sets the gate drive current: I_pulldown = (3.3 - Vbe)/R2. In this example I_pulldown = (3.3-0.7)/2.5K roughly 1mA.
Set R1 based on desired Vgs of mosfet:Vgs =(R1/R2) * (3.3-Vbe).
Gate pull up will be comparable but a bit slower than pull down due to RC effects. (when BJT turns off).
Setting R2 is a trade off between on IQ and gate switch speed, but works for low speed applications (~100us to 1ms switch time)

Waveforms in QSPICE look really clean, but still need to test on breadboard:
1702913467510.png
1702913505530.png
 

Ian0

Joined Aug 7, 2020
10,054
It’s pretty good as long as you don‘t need high frequency switching.I’d put a zener between gate and source just to be on the safe side. Any voltage between 10V and 18V.
 

crutschow

Joined Mar 14, 2008
34,697
The circuit with the NPN should work.

The one with the PNP won't, since the collector-base junction is forward-biased by the plus supply voltage.
A PNP needs a negative voltage from collector to base for normal transistor operation.
 

AnalogKid

Joined Aug 1, 2013
11,148
I would use this arrangement with a 10 volt zener diode.
You still need a resistor across the zener to assure rapid and complete turn-off. I just measured a 12 V zener, and got 4.x Mohm in one direction and open circuit in the other.

The FET's input capacitance and the added resistor determine the turn-off time. With a typical value of 1.2 nF, a 100 K resistor yields a fall time of approx. 360 us (to 3 time constants).

ak
 

crutschow

Joined Mar 14, 2008
34,697
I would use this arrangement with a 10 volt zener diode.
You also need a resistor (e.g. 10kΩ) across the Zener to discharge the gate capacitance and turn off the MOSFET.

And R1 needs to be a 1W resistor, since is dissipates about 1/2W when Q1 is on.
 

Ian0

Joined Aug 7, 2020
10,054
You also need a resistor (e.g. 10kΩ) across the Zener to discharge the gate capacitance and turn off the MOSFET.

And R1 needs to be a 1W resistor, since is dissipates about 1/2W when Q1 is on.
Current through R1 is (3.3V-Vbe)/2.5k = 1mA
So power in R1 is 1mA^2*12.5k = 12.5mW
 

Ian0

Joined Aug 7, 2020
10,054
The second circuit is potentially useful with a bit of rearrangement:
Make Q2 NPN, and connect the base to 3.3V
Then you have a common-base circuit which will drive the MOSFET. Its only disadvantage is that it is limited to the amount of current available from your logic output that drives unit.
 
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