3600 Printer Maintenance Manual
Motor Driver
The motor driver circuit of the 3600 consists of ICs U2, U21, U17, and U19; discreet parts Q16, Q1, Q3, Q4, Q6, Q11, Q12, Q13, Q14; and associated diodes, resistors, and capacitors. The eight
When a phase is driven or turned on, one FET on each end of a phase is turned on. One of the FETs will be a high side FET putting 50 volts on one end of the winding. The other FET will be a low side FET putting zero volts on that end of the winding.
When the motor is running the windings are being excited first with 50 volts on one end, and then the 50 volts on the other end. At no time are both FETs on the same end of a winding on at the same time.
When a winding is turned on, the current is first monitored and then controlled by turning the FETs on and off at a high rate. This is called pulse width modulation. The current in the winding is monitored measuring the voltage across the sense resistors R18, R22, R97, and R99. These voltages are called sense_A1 and sense_B1. These voltages are inputs to U2. U2 is a comparator that compares a reference voltage (voltage at U2 pins 2 and 6) to the voltages sense_A1 and sense_B1. When these voltages become greater than the sense voltage the associated out put of U2 switches from low to high. This voltage is fed into the GAL U21 and then to the appropriate driver IC U17 or U19 which turns the associate FET off. The off time during this pulse width modulation cycle is constant and controlled by the C109, R127 for sense_A1 or C42, R137 for sense_B1.
The reference voltage on pins 2 and 6 of U2 is established by the pulse width modulation input M5. This is an input from the microprocessor to Q15 through R108. The duty cycle of this signal controls the reference voltage input to U2. The magnitude of this voltage establishes the magnitude of the current in motor windings.
Other inputs from the microprocessor to the GAL U21 circuit are M1, M2, M3, and M4. These inputs control the stepping of the motor. They go into the GAL where they are decoded and fed into the driver ICs U17, U19 which turn the FETs on and off.
Reset is the last input to the motor driver circuit. U19 pin 3 is high when reset is applied to the DISABLE input of U17. This action ensures that all the FETs are held in the off condition to control start up and shut down transients.
