Panasonic KX-MB1520FX7, Service Manual

Page: 41 / 396

41
KX-MB1520FX7/KX-MB1520FX8/KX-MB1520FXW/KX-MB1530FX7/KX-MB1530FXW
"DIRAB"(IC502_pin38) and "DIRCD"(IC502_pin47) determine the direction of motor rotation.
The relation between these signals and motor rotation directions are shown in below table.
After setting the above signals, clock signal is supplied from IC300_pinA10 to "CLKAB"(IC502_pin39) and "CLKCD"
(IC502_pin46).
Whenever clock signal is supplied, current value and direction supplied to Scan motors change according to the excitation mode
which is determined by above signal levels.
The clock frequency also determines the motor speed.
6.7.3.2. Motor current control circuit
1. Function
According to the scan speed, motor current is controlled for appropriate value.
For example, when scan speed is low, motor has enough driving force.
So to prevent the vibration and noise during motor rotation, motor drive current should be reduced.
When scan speed is high, motor needs much driving force. so much current should be supplied.
In order to control the motor current, VREFAB and VREFCD voltages of IC502 is controlled.
When VREFAB and VREFCD voltages are high, motor currents are increased, and the voltages are low, motor currents are
reduced.
2. Circuit Diagram
Please refer to the circuit diagram shown in the block diagram of FB (Flat bed) motor drive circuit (KX-MB1520) (P.38).
3. Circuit explanation
For the sake of VREFAB and VREFCD voltage control, PWM pulse is supplied from IC300_pinD8.
PWM pulse is integrated by R671, R672 and C657, then converted to DC voltage.
This DC voltage is supplied to VREFAB and VREFCD pins of IC502.
When duty of PWM pulse is high, VREFAB and VREFCD voltages are increased and when duty is low, VREFAB and
VREFCD voltages are decreased.
4. Timing chart of current control
Following timing charts are the example of VREFCD voltage corresponding to PWM pulse duty.