Futterama
Member
Hi,
I'm building a H-bridge full bridge circuit for controlling a windshield wiper motor (around 2A unloaded) and it keeps burning the MOSFETs and MOSFET drivers.
A PIC16F1825 is connected to the TC4424's, directly from PIC pins to TC4424 inputs. I'm using the built-in PWM controller in the PIC.
The 2 inputs on the TC4424 that controls the lowside FETs, have a pulldown resistor of 100k. All the FETs have a 100k pulldown resistor on the gate. I know this will actually turn on the high side FETs during the power up time where the PIC is initializing but I forgot all about the pulldowns until I was soldering my PCB and it was hard to pull the gates to Vin due to the PCB layout, and I guess it doesn't matter since the lowside FETs are off during power up.
The lowside FETs are FDP8896 (N-Channel, 30V, 92A, 5.9mOhm) and the highside FETs are NDP6020P (P-Channel, -20V, -24A, 50mOhm). These are mounted on a heatsink and are electrically isolated using thermal pads and nylon washers for the screws.
The PIC is powered from a 7805 and Vin is 12-15V.
I have had the circuit working just fine and my code seems to work like it should, I could run the motor at different duty cycles and different frequencies.
The latest burnout happened today when I was testing the motors ability to run slow at 10% PWM duty and at different frequencies. I was running the unloaded motor at a frequency and would just change it in my code, so I disconnected the circuit from Vin, did the quick change in code, recompiled, reprogrammed the PIC and connected the Vin again, this took around 10-15 seconds. My 20A powersupply went into overload and I quickly saw the amp-meter showing 23A and it smelled funny and I quickly disconnected the power again. The one TC4424 driver was toast and the MOSFETs connected to it was unable to turn off (I disconnected them from the circuitand tested them individually).
Any idea what went wrong?
It seems to happen when I connect the power, so I was thinking maybe the lowside pulldowns are too big and didn't discharge the gate while the power was disconnected and then one of them were on when I reconnected the power. Or maybe I really need to add pullups to both the drivers input for the highside FETs and also to the highside FET gates.
I'm building a H-bridge full bridge circuit for controlling a windshield wiper motor (around 2A unloaded) and it keeps burning the MOSFETs and MOSFET drivers.
A PIC16F1825 is connected to the TC4424's, directly from PIC pins to TC4424 inputs. I'm using the built-in PWM controller in the PIC.
The 2 inputs on the TC4424 that controls the lowside FETs, have a pulldown resistor of 100k. All the FETs have a 100k pulldown resistor on the gate. I know this will actually turn on the high side FETs during the power up time where the PIC is initializing but I forgot all about the pulldowns until I was soldering my PCB and it was hard to pull the gates to Vin due to the PCB layout, and I guess it doesn't matter since the lowside FETs are off during power up.
The lowside FETs are FDP8896 (N-Channel, 30V, 92A, 5.9mOhm) and the highside FETs are NDP6020P (P-Channel, -20V, -24A, 50mOhm). These are mounted on a heatsink and are electrically isolated using thermal pads and nylon washers for the screws.
The PIC is powered from a 7805 and Vin is 12-15V.
I have had the circuit working just fine and my code seems to work like it should, I could run the motor at different duty cycles and different frequencies.
The latest burnout happened today when I was testing the motors ability to run slow at 10% PWM duty and at different frequencies. I was running the unloaded motor at a frequency and would just change it in my code, so I disconnected the circuit from Vin, did the quick change in code, recompiled, reprogrammed the PIC and connected the Vin again, this took around 10-15 seconds. My 20A powersupply went into overload and I quickly saw the amp-meter showing 23A and it smelled funny and I quickly disconnected the power again. The one TC4424 driver was toast and the MOSFETs connected to it was unable to turn off (I disconnected them from the circuitand tested them individually).
Any idea what went wrong?
It seems to happen when I connect the power, so I was thinking maybe the lowside pulldowns are too big and didn't discharge the gate while the power was disconnected and then one of them were on when I reconnected the power. Or maybe I really need to add pullups to both the drivers input for the highside FETs and also to the highside FET gates.
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