Question about gate driver use at voltage above microcontroller voltage

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
Hey guys,

So I need to switch a mosfet with the drain voltage at 30 volts and the source voltage at 25 volts. The gate driver is has a Vdd of 40 volts and a Vee at 25 volts. Can I control the gate driver with 5 volts or is that impossible? Do I have to use an optical coupling? What are my options? All input is helpful and appreciated!

-khan
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31

crutschow

Joined Mar 14, 2008
34,855
Would they work?
No.
Those are just two complementary emitter follower transistors in one chip, that give a current gain but no voltage gain.
Thus their output voltage can be no greater than the input signal voltage.

At what speed do you want to drive the MOSFET?
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
No.
Those are just two complementary emitter follower transistors in one chip, that give a current gain but no voltage gain.
Thus their output voltage can be no greater than the input signal voltage.

At what speed do you want to drive the MOSFET?
The most will be turned on/off maybe once per second
 

Alec_t

Joined Sep 17, 2013
14,417
...... Then a shifter/driver like either of these (depending on whether a high power or low power FET is being driven) should work :-
LevelShiftDrive.PNG
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
...... Then a shifter/driver like either of these (depending on whether a high power or low power FET is being driven) should work :-
View attachment 119774
Sorry Alec t, didn't have much time to respond to his morning. So basically the circuit is a voltage divider controlled by a mosfet that controls the gate driver? Given r2 and r2, won't the output voltage be 20 volts which is less than vee and not enough to drive the transistor? Perhaps may need to change the resistors?
I like that but is there something more simple like a single device that can accomplish this? I'm trying to simply my circuit as much as possible.
 

shortbus

Joined Sep 30, 2009
10,049
When I hear "gate driver" I automatically think, gate driver IC. As far as I know they (IC's) can be triggered by a micro controller output voltage. They come in many types, low side, high side, and half bridge. Have a look at these since only you know what you need - https://www.google.com/search?q=mosfet+gate+driver+ic&ie=utf-8&oe=utf-8 The mosfets themselves determine the voltages being controlled, not the driver. Most drivers have a ~500V or more isolation between the mosfet and the triggering signal built into them, so optical isolation shouldn't be needed.
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
When I hear "gate driver" I automatically think, gate driver IC. As far as I know they (IC's) can be triggered by a micro controller output voltage. They come in many types, low side, high side, and half bridge. Have a look at these since only you know what you need - https://www.google.com/search?q=mosfet+gate+driver+ic&ie=utf-8&oe=utf-8 The mosfets themselves determine the voltages being controlled, not the driver. Most drivers have a ~500V or more isolation between the mosfet and the triggering signal built into them, so optical isolation shouldn't be needed.
The reality is, I'm not really sure what I need but I am trying to figure it out. Basically I need to switch a mosfet with current and voltage between drain and source of 2 to 3 amps 30 and 25 volts . I also have upto 40 volts to drive the mosfet if necesary. The microcontroller is at 0 to 5 volts. What would be a good gate driver ic for me in this case? The mosfet I am using is: http://www.mouser.com/Search/ProductDetail.aspx?R=FQP13N06Lvirtualkey51210000virtualkey512-FQP13N06L
 

MrChips

Joined Oct 2, 2009
31,107
You can also use an opto-coupler.
The microcontroller turns on/off an LED in the opto-coupler with a suitable current limiting series resistor.
The output of the opto-coupler can be used to switch the gate voltage at the desired control voltage.
The only limitation is the speed of switching. What is the maximum frequency of the desired output?
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
You can also use an opto-coupler.
The microcontroller turns on/off an LED in the opto-coupler with a suitable current limiting series resistor.
The output of the opto-coupler can be used to switch the gate voltage at the desired control voltage.
The only limitation is the speed of switching. What is the maximum frequency of the desired output?
Thanks for the info. Rather than using a separate opto-coupler, is there a gate driver that contains an internal optical coupling? As in I just want to simply things and use as little components as possible.
 

Alec_t

Joined Sep 17, 2013
14,417
Note that a lot of driver ICs rely on a 'bootstrap' arrangement which requires the lower end of a capacitor being rapidly pulled high and low repeatedly to create a gate voltage 10V or so higher than the FET source voltage. This may not work reliably if you switch at a 1 sec rate.
I'm still not clear exactly how your FET is associated with the various supplies and a load. Can you post a sketch/schematic?
So basically the circuit is a voltage divider controlled by a mosfet that controls the gate driver? Given r2 and r2, won't the output voltage be 20 volts which is less than vee and not enough to drive the transistor?
There are no MOSFETs in the circuits I posted, other than the one you are intending to drive. The circuit is not a controlled voltage divider. R2 is a pull-up resistor for Q2 base, so that the FET gate voltage will be driven close to 40V. R3 is a pull-down resistor for Q3 base to drive the FET gate voltage close to 25V (Vgate = 25V-Vcb+Vbe = ~ 25V when Q3 conducts). The traces in the pic I posted are the result of an LTspice simulation and show the expected approximately 25V-40V swing (yellow trace = first circuit, blue = second circuit).
 

crutschow

Joined Mar 14, 2008
34,855
The reality is, I'm not really sure what I need but I am trying to figure it out. Basically I need to switch a mosfet with current and voltage between drain and source of 2 to 3 amps 30 and 25 volts . I also have upto 40 volts to drive the mosfet if necesary. The microcontroller is at 0 to 5 volts. What would be a good gate driver ic for me in this case? The mosfet I am using is: http://www.mouser.com/Search/ProductDetail.aspx?R=FQP13N06Lvirtualkey51210000virtualkey512-FQP13N06L
Since we are somewhat guessing at this, here's the LTspice simulation of a circuit using an opto that I think does what you want.
The MOSFET you selected is a logic level type that needs only a Vgs of 5V to fully turn on, so you don't need the 40V for the gate driver.
Look okay?

upload_2017-2-2_10-14-41.png
 

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Thread Starter

bkhan10000

Joined Jan 18, 2017
31
Since we are somewhat guessing at this, here's the LTspice simulation of a circuit using an opto that I think does what you want.
The MOSFET you selected is a logic level type that needs only a Vgs of 5V to fully turn on, so you don't need the 40V for the gate driver.
Look okay?

View attachment 119789
Thank you so much, crutschow. Looks like exactly what I need. Will go and try it out.
 
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