Kyocera FS-1010 service manual Heater lamp control circuit, heater lamp control circuit

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.

Engine board

33 THERMA			Heater lamp control circuit
P10/ANI0
	+5V			+5V	+5V
CPU	R52	2	U04-1		Q11
U01			−	1
	GND
		3	393
			+
	R56				QA03-b
1	GND	GND
	HEAT
P50/A8						GND
					QA03-a
43	ZCROSS
P00/INTP0
	Power supply unit				Bias
AC input					board
Thermal cutout				Zero
				cross
				signal		High
Heat roller			detection			voltage
		+24 V		circuit		board
Heater lamp
	Triac			(PC2)
		Photo-triac
	(TRC1)
Thermistor

Figure 4-3-5 heater lamp control circuit

FS-1010

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