Hello. I am driving a unipolar stepper motor from a PIC 16F877. The PIC outputs the sequence on its pins correctly and the pulses are observed to be correct on the oscilloscope (meaning that they have a maximum value of 5 volts). The drive circuit of the motor is also correct. If I apply 5 volts to the gate of any of the 4 MOSFETs, that phase draws the correct current and the shaft moves to that phase. The problem happens when I connect the gates of the MOSFETs to the PIC pins. There is suddenly a voltage drop that causes the pulses to have a maximum value of 2 volts or something instead of 5 volts, which is not enough to turn the MOSFETs ON and hence operate the motor. I have pull-down resistors on the gates of the MOSFETs as well in order to turn a MOSFET off when the pin is floating. The strange thing is that the motor was operating just fine before. This just happened today. Can anyone help me locate my problem? Thanks a lot.
Nichola V. Abdo.
Nichola V. Abdo.