This reference design demonstrates a multi-channel solid state relay (SSR) using a single isolation. The design uses a multi-channel digital isolator with a single isolated power supply and common ground gate-drive circuit to control multiple SSRs independently. The design is rated for 24-VAC powered relays with current rating up to 2 A, but scalable up to 240 VAC and higher current rating. Each SSR channel consumes less than 75-mm2 space with a maximum height of the component around 3-mm, enabling considerable size saving compared to electromechanical relays. The use of single isolated power supply reduces board space and BOM cost.
          Features
          
          - Multiple solid-state relays using a single isolation with multichannel digital isolator, easily scalable to any number of SSR channels with minimum extra cost
 - SSR drive voltage 24 VAC ±20%, drive current 2-A RMS (voltage and current rating, scalable by using appropriately rated components)
 - SSR turn on and turn off time: 15–300 μs (adjustable), average current consumption per SSR drive (referred to primary) < 4 mA (adjustable down to 20 μA per channel)
 - SSR size < 75 mm2 per channel. Height is around 3 mm.
 - Functionally isolated open-loop flyback based power supply without the need of an MCU
 - Surge and switching overvoltage protection