The function of the OCMOS FET (SSR) is that of a relay, and therefore it has the same make and break functions as a conventional mechanical relay.
In the same way that a mechanical relay has several kinds of make and break functions, some variation can be seen also in the OCMOS FET (SSR).
The following "Form a", "Form b", and "Form c" categories are taken from the names given to mechanical relays.
"Form a: Normally-Open (N.O.)"
at no input current, output side is opened.
The "Form a" is an "open" type where when the current flows into the primary side LED, the secondary side closes and the current passes through; conversely, when the current doesn't flow into the primary side (normally), the secondary side opens. Thus it is called "normally-open". As this open state acts as an off-switch, it is also called "normally-off".
Among the OCMOS FET (SSR) range, the PS7xxx-1A and -2A OCMOS FET (SSR) are equivalent to this "Form a".
"Form b: Normally-Close (N.C.)"
At no input current, output side is closed.
The "Form b" is a "closed" type and performs the opposite operation to the "Form a": when the current flows into the primary side LED, the secondary side opens; conversely, when the current doesn't flow into the primary side (normally), the secondary side closes, hence the name "normally closed". This closed state acts as an on-switch and so it is also called "normally on".
Among the OCMOS FET (SSR) range, the PS7xxx-1B and 2B are equivalent to this
"Form c: (N.C.)+(N.O.)"
"Form a" and "Form b" were built-in one package.
The "Form c" pairs the "Form a" and the "Form b". In the case of a mechanical relay, the function would be that of a circuit switch, however in terms of the "Form c" OCMOS FET (SSR), it has integrated the 2 OCMOS FET (SSR) "Form a" and "Form b" types into one package. This OCMOS FET (SSR) has two primary and secondary sides; however, if the primary side LEDs are connected outside in series, and if the 2 MOS FETs on the secondary sides are connected in series and make a common terminal from the connected point, the function becomes similar to that of the mechanical relay "Form c". As this type's function is not merely make and break, it is called a "Transfer Type".
Take care to remember that the operations of the OCMOS FET (SSR) "Form c" differ in many ways to those of a mechanical relay: the mechanical relay normally has one input, and it is fundamentally impossible to conduct both a/b contacts simultaneously, whereas with this OCMOS FET (SSR), there are 2 inputs, and to perform both the a/b contacts independently, and to make the transfer-type perform precisely (i.e., to avoid both the Form a/b contacts conducting simultaneously), it is necessary to regulate the timing of the 2 input signals.
Among the OCMOS FET (SSR) range, the PS7xxx-1C is equivalent to this "Form c".
OCMOS FET (SSR) (PS7XX-1C)