The reference design demonstrates a multichannel solid state relay (SSR) using a single isolation. The design uses a multichannel 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.

• 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 around 3 mm
• Low-cost, functionally isolated open-loop flyback based power supply, without the need of an MCU
• Surge and switching overvoltage protection

• Thermostat
• HVAC Controller