S742

1 Form A

Solid State Relay

PERFORMANCE DATA

0

10

20

30

40

600 610 620 630 640 650 660 670

Blocking Voltage (V)

S742

Typical Blocking Voltage Distribution

N = 100, Ambient Temperature = 25°C

0

500

1000

1500

Tem perature (C)

S742

Maximum Load Current vs. Temperature

5 V

Threshold

Input Signal

SCR #1 Turns On when

5V threshold is reached.

SCR #1 Turns Off,

SCR #2 Turns On

at Zero Volts.

SCR #2 Turns Off,

SCR #1 Turns On

at Zero Volts.

SCR #1 and Relay Turn

Off at Zero Volts.

5

4

2

6

3

1

Relay Input Signal is

Turned On.

Relay Input Signal is

Turned Off.

This solid state relay has been designed with a driver circuit that controls the operation of two back-to-back silicon controlled rectifiers

(SCRs), each responsible for one half of the AC cycle. If an AC signal is examined, the turn on, turn off and zero-volt switching can be seen.

Figure 1 shows a typical 60 Hz, 120Vac signal with a corresponding relay input signal:

ZERO-VOLT SWITCHING

Figure 1 shows the sequence of zero-volt switching operation. At Stage 1, an input signal is applied to the relay. The relay will not turn on

until the threshold voltage of 5V is reached. Once this point is reached (Stage 2), SCR #1 (designated as the SCR which controls positive

AC voltage) turns on. However, SCR #1 only conducts for an instant, as the cycle quickly crosses zero. At this point (Stage 3), SCR #1 will

turn off and SCR #2 (negative AC voltage) turns on. Likewise, at the next zero cross (Stage 4), SCR #2 will turn off and SCR #1 conducts

again. Even though the input signal is terminated at Stage 5, the relay will continue to conduct (typical SCR behavior) until Stage 6, when

SCR #1 crosses zero and ceases to conduct. Please note that turn on can likewise begin on the negative phase of the AC cycle with a -5V

threshold, though only the positive phase is shown here.

© 2004 Solid State Optronics • San José, CA

www.ssousa.com • +1.408.293.4600

Page 3 of 5

S742

rev 1.40 (10/25/2004)