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http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-circuit.html

I have made 2 H bridges following this schematic. I have replaced

TIP107 with TIP147

TIP102 with TIP142

The Opto-couplers are P785.

I have not included the diodes as they are internal to the TIP.

I am trying to run two small toy car motor, max 2 Amp. The power supply is 20V isolated, the plan is to PWM the ENA signal with an Arduino to adjust the Voltage to the motors. Everything seems to work just fine on the bench. However after a few minutes of running and stalling under load, the TIP seem to get quite hot and the motors stop responding in the direction the stall happened. The other side seems to be unaffected. When trying again after a few minutes, the affected side just gets hot, but no motion from the motor, while the unaffected side seems to work fine. I have already replaced the TIPs a few times, a multimeter test shows some transistors don’t turn off anymore, last time both PNP had continuity between collector and emitter with all power off. I went over and over the control circuit, there seems to be no problem there. Is there anything I might be getting wrong? I have to invert the PWM value in the code,

PWMValue= (255-PWMValue)

as the sides are actually active when ENA is low, so I am not sure if this is causing any problems, but as I said without load the motors run just fine.

Thanks in advance

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