Panasonic UF-5500, Service Manual

Page: 41 / 365

41
UF-5500 / 4500
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
3. Timing chart
Following timing charts are the example when PWM pulse duty are approx 9% and 45%.
Current control Block
IC700
ADF motor
OCP Block
3.3V
C
509
R
533
Q521 R534
IC300
R538
R
539
PWD
D8
A
B C
R
540
Vref
PS
22
20
ADFMEN
D9
Q700
R701
R702
R711
Approx. 2.4V
30KHz
30KHz
Approx. 1.2V
PWM Duty 9% PWM Duty 45%
(A)
PWM pulse
(B)
Drain of Q521
(C)
Vref