Ae (Auto Exposure) Sensor Circuit - Sharp SF-2020 Service Manual

(9) AE (Auto Exposure) sensor circuit

The AE sensor circuit is composed of the AE sensor PWB; which is composed of the photo diode, the I-V convertor circuit, and the amplifier circuit;
and the amplifier circuit on the control PWB.
CPU
AES
AN0
AEG1
I/O
AEG0
Operation amplifier A performs I-V conversion of the original density level (minute current) from the sensor. Operation amplifiers B and C amplify 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 I/O chip when test command SIM 47 is
executed.
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.
(10) Toner supply motor drive circuit
IC104 is the motor control IC which drives the toner supply motor with
the pulse signals (TMa, TMb) outputted from the I/O chip.
+5V
TMa
TMb
I/O
R20 R211
47KJ 47KJ
(11) Reset IC (IC13)
1
General
The M51953 BL is the semiconductor IC most suitable to detect the
power voltage and reset the logic circuit of every type including the
CPU.
It is provided with the built-in delay circuit. Delay time is easily ob-
tained by adding external capacity.
Pin connections (Top view)
External view 5P5
+24V
R40
1
1KJ
IC14A
C38
LM324
ZD2
HZS883
1000PF
+24V
IC5
C2
6 +
2
8
9 10UF35V
IN1
7
1 TMa
IN2
3 TMb
5
GND
TA7291S
M
5 Output
4 Delay capacity
3 GND
2 NC
1 Power
R50 100KJ
4
R53
2 C48 0.1µ F
3 1KJ
6
7
11
5
IC14B
LM324
R44 R43 R45 R47
15KF 750F 75F 270F
AEG1
AEG0
Truth value table
Input
TMa TMb
L
H
L
H
∞: High impedance
Internal circuit
+5V
2
Protection
circuit
(Heat insulated)
9
TMa
TMb
12 – 14
PDK
PDA
R48 C49
100KJ
2200PF
AE sensor PWB
Output
TMa TMb
∞ ∞
L
L H L
H L H
H L L
+24V
8
REG
1 5
GND
4
Mode
Stop
CW/CCW
CCW/CW
Break
6 +24V
TMa
7
M
3
TMb
pin = NC pin