Heater Lamp Control Circuit - Sharp SF-2220 Service Manual

(6) Heater lamp control circuit

D16
DSM101
PR Q5
8 ~ 20
2SA573
R54 R5 3
5.6KJ 47KJ
General
1
The heater lamp control circuit detects the heat roller surface temper-
ature with the thermistor, converts it into a voltage, and outputs it to
the CPu analog input pin.
The CPU converts analog signals into digital signals, compares them
with the value set by test commands to turn on/off the heater lamp,
maintaining the heat roller surface temperature at a constant level.
The higher the heat roller surface temperature is, the greater the
thermistor resistance is, and vice versa.
Therefore, the lower the heat roller surface temperature is, the higher
the thermistor pin voltage is. The thermistor pin voltage is inputted to
the analog port of CPU, which controls ON/OFF of the heater lamp
according to the input voltage level.
13
IC20D
NJM2901
14
IC20C
D6 D7
NJM2901
+24V
IC9
16 1
I1
O1
15 2
O2
I2
14 3
O3 I3 R32
13 4
O4 I4
12 5
O5 I5 2.7KJ
11 6
O6 I6
10 7
I7
O7
9 8
SK
G
ULN2004
R35
270J
1/4W
10K
2.2K
Q3
DTA123Y5
MC-Service
R67 R7 1
1KJ 47KJ
11
R7 5
10
Q7
2SC945
75J
C7
R6 8
5.6KJ
0.22µ F
R91 R87 R89
8.2KJ 1MJ 4.7KF
8
D3 8
9
MA700
C55
R93
R9 2
680J
47KF
22000PF
PR
CPU
HL
AN1
PR
L2
+5V2
PR
AC PWB
AC
N1
[High temperature protect circuit when the CPU is hung up (out
of control)]
1) The IC20 8 pin voltage (reference voltage) is divided by R91 and
R93. The thermistor pin voltage is inputted to the IC20 9 pin.
When the voltage at 9 pin becomes lower than the voltage at 8 pin
(the heat roller surface temperature about 240V), the IC20 14 pin
is driven to LOW, pulling down the PR signal to the GND level,
turning off the AC power of the heater lamp.
2) Since the OP-latch signal is fixed to HIGH or LOW, the collector of
Q7 is open. The voltage at IC20 10 pin is higher than the voltage
at IC20 11 pin (reference voltage), and IC20 13 pin is driven to
LOW.
With the above operations, IC9 13 pin is opened to turn off Q5,
turning off the power relay. As a result, the AC power of the heater
and the copy lamp is turned off.
* The double protection with 1) and 2) is provided.
12 – 12
+5V1
C6
R80
OP-LATCH
CPU 17PIN
24KJ
R84
0.22µ F
D41
10KJ
Vref
Heat roller
GATE
T1
T2
GND
AC PWB
200V AREA
MLSW
ML
MLSW
ML
ML : 1KW