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H-bridge DC motor driver with OPAMP as gate driver?

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suku:
I'm designing a circuit where I drive a 12V 500mA DC brushed motor using a H-Bridge MOSFET IC (DMHC3025LSD or really any suitable FET pair).

https://hu.mouser.com/datasheet/2/115/DMHC3025LSD-709448.pdf

I designed simple opamp based driver circuit that will take a GPIO output from 5V microcontroller and output the gate signals for the FETs.



DRIVER_P1, DRIVER_P2, DRIVER_N1 and DRIVER_N2 are connected to the microcontroller. Pullup and Pulldown reistors are to make sure that the motor won't start while the microcontroller is in reset state. I will add zener clamps to make sure not to damage the GPIO pin with the 12V.

MOTOR+ and MOTOR- are connected to the DC motor

VDD+12V is +12V.
VSS+12V is the Ground for the 12V supply.
VREF is 2V.

Design goals: Low cost, high reliability operation, reliable supply chain for the components.

Will this circuit work well? What are some things to look out for when designing motor drivers? Should I use integrated motor driver chip? I'm looking for any feedback!
 Thanks.

David Hess:
There is nothing inherently wrong with that if you do it right unless you need better performance.  Operational amplifiers make slow comparators and they become even slower when driving the relatively high input capacitance of power MOSFETs.

The LM324 is tame enough to work well as a comparator if the result is fast enough for you.  I would put low value series resistors between the LM324 outputs and the power MOSFET gates to limit the current at the expense of a little bit of speed.  In through hole designs, these resistors would also help with layout.

If the LM324 does not pull up far enough to its positive supply to completely shut off the p-channel power MOSFETs, then add a pull-up resistor to its output.

Benta:
Is this for static drive, or do you intend PWMing the motor?
Also, why the diodes? The MOSFETs already have reverse diodes.

suku:
I want to be able to PWM the motor. Does that require any special consideration?

Zero999:

--- Quote from: David Hess on June 24, 2019, 06:50:50 pm ---If the LM324 does not pull up far enough to its positive supply to completely shut off the p-channel power MOSFETs, then add a pull-up resistor to its output.

--- End quote ---
But then that problem could be shifted to the negative side of the bridge.

The easiest fix is to replace it with a comparator, such as the LM339 (note the different pin-out) and a pull-up resistor from each gate to +12V.


--- Quote from: suku on June 24, 2019, 08:23:20 pm ---I want to be able to PWM the motor. Does that require any special consideration?

--- End quote ---
The LM324 will not do for PWM. The MOSFETs will switch very slowly, which will cause them to get very hot. You need a proper gate drive IC, such as the TC4468.
http://www.farnell.com/datasheets/2124840.pdf?_ga=2.221062353.878591148.1561408095-1107606318.1553553996

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