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FS-1010
Heater lamp control circuit
Activation of the heater lamp is dominated by the HEAT signal which is derived by the engine CPU
(U01) at its pin #1. When its level is high, transistor QA03-a turns on, photo-triac PC2 and triac
TRC1 turn on simultaneously, and the heater lamp is applied with the primary AC voltage in turn.
Switching of triac TRC1, as affected by the HEAT signal is made in synchronization with the zero-
cross signal ZCROSS which is generated by the power supply unit. The zero-cross signal detector
watches the transition of alternating plus and negative current and detects the zero crosses. This
detector derives the resultant ZCROSS signal at its pin #43 of the engine CPU (U01). Since abrupt
change in the current flow can be significantly avoided by synchronizing triac TRC1 with the zero-
cross signal, the possibility of noise due to the primary AC supply is greatly reduced.
Figure 4-3-5 heater lamp control circuit
HEAT
ZCROSS
GND
QA03-a
QA03-b
GND
2
3
1
GND
Q11
+5V
+5V
+5V
GND
R52
R56
+
−
393
U04-1
THERMA
33
P10/ANI0
P50/A8
P00/INTP0
1
43
CPU
U01
Power supply unit
Bias
board
Engine board
High
voltage
board
Heat roller
Thermal cutout
Heater lamp
Thermistor
AC input
Tr iac
(TRC1)
Zero
cross
signal
detection
circuit
+24 V
Heater lamp control circuit
(PC2)
Photo-triac