Scanner Motor Drive Circuit - Panasonic UF-5500 Service Manual

6.7.2.

Scanner Motor Drive Circuit

General
Scanner motor drive circuit is consist of motor current control circuit, ADF (Auto Document Feeder) motor driver and OCP (Over
Current Protection) circuit.
6.7.2.1. Motor current control circuit
1. Circuit explanation
According to the scan speed, each motor current is controlled for appropriate value.
When scan speed is low, motor current is reduced to prevent the vibration during motor rotation.
When scan speed is high, motor needs much driving force. so much current should be supplied.
For the control of motor current, Vref voltage of each motor driver is controlled.
When Vref voltage is high, motor current is increased, and the voltage is low, motor current is reduced.
In order to control the Vref voltage, PWM pulse is supplied from IC300 pin D8.
PWM pulse is inverted by Q521 and integrated by R533, R534, and C509, then converted to DC voltage.
This DC voltage is supplied to Vref pin of each motor drivers.
When duty of PWM pulse is high, Vref voltage is decreased and when duty is low, Vref voltage is increased.
For ADF motor, motor current is controlled approx. 0.5A.
2. Circuit diagram of current control and OCP circuit
IC300
PWD
ADFMEN
3. Timing chart
Following timing charts are the example when PWM pulse duty are approx 9% and 45%.
(A)
PWM pulse
(B)
Drain of Q521
(C)
Vref
Current control Block
3.3V
A
Q521
R538
D8
D9
PWM Duty 9%
30KHz
Approx. 2.4V
B
C
R534
R711
Q700
R701
41
IC700
22
Vref
20
PS
ADF motor
OCP Block
R702
PWM Duty 45%
30KHz
Approx. 1.2V
UF-5500 / 4500