Datasheet

SN55107A, SN75107A, SN75107B, SN75108A
DUAL LINE RECEIVERS
SLLS069D – JANUARY 1977 – REVISED APRIL 1998
18
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
temperature controller with zero-voltage switching
The circuit in Figure 22 switches an electric-resistive heater on or off by providing negative-going pulses to the
gate of a triac during the time interval when the line voltage is passing through zero. The pulse generator is the
2N5447 and four diodes. This portion of the circuit provides negative-going pulses during the short time
(approximately 100 µs) when the line voltage is near zero. These pulses are fed to the inverting input of one
channel of the SN75108A. If the room temperature is below the desired level, the resistance of the thermistor
is high and the noninverting input of channel 2 is above the reference level determined by the thermostat setting.
This provides a high-level output from channel 2. This output is ANDed with the positive-going pulses from the
output of channel 1, which are reinverted in the 2N5449.
Heater
Load
2B
120 V to
220 V, 60 Hz
5-V
Zener
– T
Thermostat
Setting
GND
Channel 1
Channel 2
10-V
Zener
250 µF
2N5449
2N5447
250 µF
V
CC +
V
CC –
1A
1B
2A
+
+
SN75108A
Figure 22. Zero-Voltage Switching Temperature Controller