This reference design shows how to achieve zero cross switching (ZCS) with a solid-state relay. The reference design features the TPSI3050-Q1 isolated switch driver. TPSI3050-Q1 device integrates a laminate transformer to achieve isolation while transferring signal and power to the secondary side. This removes the need for any isolated bias supply. In addition, the TPSI3050-Q1 device can supply auxiliary current (IAUX) to external circuitry located on the high voltage (HV) side. Zero-cross switching is done while maintaining signal isolation between the low voltage (LV) and HV side. This reference designed achieved a 12-V, 200-us delay ZCS with a 110 VRMS, 60 Hz AC source.