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AC switches are silicon devices that control AC loads directly connected to the AC mains. This means that the driving reference terminal of the AC switch can be connected to the Line potential. This circuit explains the need of an insulation layer for the control unit and the way to implement it for an AC switch device.

It was thought in the past that connecting an MCU to the Line should be avoided as it will lead to poor appliance immunity. But it has been demonstrated over the years that such topology provides good immunity. Connecting an MCU supply to a stable nRn-flRDWLng UHIHUHnFH LV HYHn EHWWHU for immunity.

Safety insulation should be provided between accessible parts and high-voltage circuits to protect end users against electric shocks. It’s not required to ensure safety insulation by insulating low-voltage control circuits (like MCU) from high-voltage parts ( like AC switches). In fact, the insulation could be implemented elsewhere— for example, on the keyboard to which the end user has access—leaving the MCU connected to the Line. This could be cost-effective as a non-insulated power supply and non-insulated