Sharp SF-2014 Service Manual page 121

(5) Driver circuit (Solenoid, magnetic clutch)
1 General
The control signals of each load outputted from the CPU and I/O
cannot drive the load directly. The output, therefore, is delivered to
the load through the driver IC.
2 Operation
The driver circuit forms a Darlington circuit with two transistors to
obtain a large drive current (load current) from a small input current
(I/O output current). When the driver input voltage is HIGH (+5V), the
transistor is turned on to flow a current in the arrow direction, operat-
ing the load. When the driver is turned on, the driver output pin
voltage is 0V.
I/O
Output
(7) AE (Auto Exposure) sensor circuit
The AE circuit is composed of the AE sensor PWB which is com-
posed of the photo diode, and the I-V convertor circuit, and the
amplifier circuit on the control PWB.
AES1
AE sensor PWB
Operation amplifier A performs I-V conversion of the original density
level (minute current) from the sensor. Operation amplifier B amplifies
the output of operation amplifier A to a suitable level for inputting to
the CPU.
The amplifying level is automatically set by selecting the AE gain
signal (AEG0 ~ AEG2) outputted from the CPU when simulations SIM
47 is executed.
(6) Stepping motor drive circuit
1 General
The driver circuit drives the lens drive motor.
A: Stepping motor phase A coil drive signal
B: Stepping motor phase B coil drive signal
A: Stepping motor phase A coil drive signal
B: Stepping motor phase B coil drive signal
+24V
LOAD
Stepping motor time chart
A
B
A
B
C150
22000PF
R152
200KJ
POK 12
R153
-
14
POA 13
+
IC111D 10KJ
LM324
R151
C149
200KJ 33PF
R157 R156 R155
5.5KF 5.6KF 30KF
R150
5.6KF
AE operation is performed by the software in the control PWB. When
a reflected ray enters the sensor, a voltage corresponding to the light
quantity is inputted to the CPU. The CPU compares the input voltage
and the copy lamp application voltage and controls the copy lamp
voltage so that the exposure level corresponds to the original density.
12 – 7
A
Phase A
+24V
Phase A
Phase B Phase B
A
B
Drive signal
A
B
C
B
24V
4
IC111A
3
R150
+
1 AE5
B
2
-
10KJ
LH324
ZD105
HZS583
R154
330KF
AGE2
AGE1
AGE0
+24V B
Lens drive
LEMT0
LEMT1
LEMT2
LEMT3
AN0
CLPWM
CPU