Using relays are a common way of switching high-power loads with electronics. If you take any microcontroller or any other digital IC, you will see that their output current on a single pin is minimal – varies around 20mA. The same situation is with voltage. Digital pin output voltage is limited to IS supply voltage like 3.3v or 5V. Usually, we need to switch loads that draw significantly higher currents and are powered from a higher voltage supply. And there, you have several options for switching loads. One and oldest method is using mechanical relays. They are still a trendy way of switching power electronics. One most significant disadvantages of using a mechanical relay is that it has moving parts with all rising problems. These are: There is a more modern solution to overcome those problems – a Solid State Relay (SSR), also known as a single-phase power controller. Instead of switching loads mechanically, SSR does this with the help of electronics.