© 2013 Solid State Optronics • San José, CA

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S113 /H/S/TR

Rev 2.00 (11/25/2013)

001769

S113

Zero Cross

800V / 0.8A

AC Solid State Relay

ZERO-VOLT SWITCHING

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 3 shows a typical 60 HZ, 120VAC signal with a corresponding relay input signal:

Figure 3 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.

Figure 3: Zero-Volt Switching Cycle

5V Threshold

(Zero Cross Voltage)

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

Load Signal

I

F

=5mA