Zero crossing switch
A zero crossing switch turns one when the sinusoidal AC voltage its zero crossing has, and switches off when the sinusoidal AC has its zero crossing. Semiconductor relays that are equipped with thyristors or triacs always switch off when the current crosses zero, because only then does the thyristor block. Switching on can, however, take place at different times, depending on the function of the solid-state relay. If the switch-on takes place at the zero crossing of the voltage, one speaks of a zero-crossing switching semiconductor relay.
In the actuator circuit of the zero-crossing switch there are usually two anti-parallel connected thyristors.
A zero-cross switch is suitable for switching ohmic loads without causing network disturbances, e.g. B. click disturbances are generated. Zero-crossing switches or zero-voltage switches are less suitable for switching inductive loads such as coils or transformers because they generate a high inrush current. Either peak switches, if transformers with an air gap in the core are switched on, or transformer switching relays for all other transformers are more suitable for this.
Most manufacturers refer to their corresponding solid state relays as zero voltage switches , which is the function of turning on. The property “zero-crossing switching” also refers to the switching-off described above when the current crosses zero, but this is not meant for the switch-on characteristics of semiconductor relays. Solid-state relays with peak switching or instantaneous switch-on characteristics are also manufactured.