SN55107A, SN75107A, SN75107B, SN75108A

DUAL LINE RECEIVERS

SLLS069D – JANUARY 1977 – REVISED APRIL 1998

18

POST OFFICE BOX 655303

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

VCC +

VCC –

1A

1B

2A

+

+

SN75108A

Figure 22. Zero-Voltage Switching Temperature Controller