Fixing Heater Lamp Control Circuit - Kyocera Mita FS-6020 Service Manual

FS-6020

(1) Fixing heater lamp control circuit

AC power
source
Fixing heater lamp
The ON/OFF action of the fixing heater lamp is controlled by the fixing heater lamp lighting ON signal (HEATON) output from
the No.62 pin of CPU (U1) of the engine/high voltage PWB. When the HEATON signal reaches the H level, the photo triac
(PC4) - Thyristor (CR1) turns on because the transistor (Q5) turns on and then the AC voltage is loaded to the fixing heater
lamp.
The HEATON signal turns ON/OFF the photo triac (PC4) - Thyristor (CR1) being synchronized with the zero cross signal
(ZCROSS) that is detected by the zero cross signal detection circuit on the power source PWB. The ZCROSS signal detects
the zero cross point (0V) where the AC power source changes between positive/negative domains and it is input to the
No.61 pin of the CPU (U1) of the engine/high voltage PWB. Since the ON/OFF operation of the photo triac (PC4) - Thyristor
(CR1) is performed at the zero cross point (0V), it can avoid the sharp change of current and restrain noises generated from
the AC power source.
2-3-4
Power source PWB
Zero
cross
signal
detection
circuit
CR1
PC4
Fixing thermistor
Figure 2-3-4 Fixing heater lamp control circuit
Engine/high voltage PWB
Pulse
Fixing heater lamp ON circuit
3
2
Q5
1
+5V1
Fixing heater
lamp ON -
Runaway prevention -
Fixing thermistor
disconnection
detection circuit
61
ZCROSS
CPU
(U1)
62
HEATON
63
HTEMPN
64
THDEAD
76
THERM