H bridge motor driver problem

Thread Starter

zgaunc

Joined Aug 22, 2021
15
Hi all, I just made a H bridge motor driver using a bread board. I followed exact schematic design attached in this post. I used Arduino board to control motor. When motor was running I took off two signal control wires from Arduino board. Most of the time the motor stopped but occasionally, the motor slow down a little then speed up to the normal and keep running. I think the motor should stop because when signal lost, the pull up resistors on the upper side of the H bridge should close the gate of the p-mosfets, so that the motor stop running. Does anyone know this problem? What is the reason and how to fix it.
Thank you
 

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ElectricSpidey

Joined Dec 2, 2017
1,882
I don't see how the values on that schematic can be correct, as per the "0" volts and the '12" volts because those resistors are creating a divider.

It seems to me when one side is pulled low, the other side would be at 6 volts. (assuming equal value resistors)

When both signals are removed both sides will be at 6 volts, not 12.
 

Audioguru again

Joined Oct 21, 2019
3,645
Hee hee, when both sides produce gate voltages of +6V then all the Mosfets are turned on causing them the short the power supply making lots of smoke.
Get rid of the gate resistors to ground.
 

Irving

Joined Jan 30, 2016
2,183
What resistor values have you used? theres nothing on the diagram and they didnt come out well in the pics.

@Audioguru again Not necessarily, if the upper ones are much smaller than the lower ones the the upper will be off and the lower on by default (inputs open).
 

Juhahoo

Joined Jun 3, 2019
222
Don't connect MOSFETS like that, there is potentially a high risk of shoot through and then you burn things.
Each of the MOSFET needs an individual control, and since you have MCU their control is so simple or use a H-bridge controller where the shoot through is prevented in hardware.
 

Irving

Joined Jan 30, 2016
2,183
Don't connect MOSFETS like that, there is potentially a high risk of shoot through and then you burn things.
Each of the MOSFET needs an individual control, and since you have MCU their control is so simple or use a H-bridge controller where the shoot through is prevented in hardware.
True. This is a better arrangement, it uses two more ports on the Arduino, but this facilitates more helpful control...

1630179679457.png
 

Audioguru again

Joined Oct 21, 2019
3,645
What resistor values have you used? theres nothing on the diagram and they didnt come out well in the pics.

@Audioguru again Not necessarily, if the upper ones are much smaller than the lower ones the the upper will be off and the lower on by default (inputs open).
With no resistor values shown I assumed they are all the same value.
Then when the transistors are both turned off, all Mosfets have a Vgs of 6V and are all turned on.
 
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