Millions of home appliances worldwide contain at least one electrical load that requires its input power to be switched on and off, and some require variable input power. For appliances where the power to a single load has to be switched on and off, a simple electromechanical switch can meet the requirement, subject to its expected shortcomings of contact sparking, conducted and radiated electromagnetic interference and limited electrical life. For appliances where the load power must be varied, a solid state power controller using a triac is most often employed because of the associated circuit's simplicity, reliability and economy.
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