Controlling AC power to inductive loads

An intelligent light dimmer device, comprising:

• a power input terminal configured for connection to an alternating current (AC) supply voltage, and a load output terminal configured to connection to an inductive load comprising a magnetic low-voltage transformer which is configured to drive low voltage lighting;
• an AC switch connected in an electrical path between the power input terminal and the load output terminal, wherein the AC switch is configured to be placed into one of a turned-on state to couple the AC supply voltage to the inductive load, and a turned-off state to decouple the AC supply voltage from the inductive load;
• and
• a control system configured to (i) generate a switch modulation control signal to switch the AC switch between the turned-on state and the turned-off state to modulate an amount of AC power that is delivered to the inductive load based on a given dimming power level setting, (ii) detect zero-voltage crossings of the AC supply voltage when connected to the power input terminal, (iii) monitor a load voltage of the inductive load when connected to the load output terminal to detect for a presence of inductive flyback voltage in the load voltage when the AC switch is switched between the turned-on state and the turned-off state for the given dimming power level setting, and (iv) in response to detecting the presence of inductive flyback voltage in the load voltage, determine for the given dimming power level setting, a delay time to place the AC switch into the turned-off state subsequent to each detected zero-voltage crossing of the AC supply voltage, so that the AC switch placed into the turned-off state at each time that substantially coincides with a zero-current crossing of load current of the inductive load, to thereby suppress the generation of inductive flyback voltage when the AC switch is switched between the turned-on state and the turned-off state for the given dimming power level setting.

A method, comprising:

• controlling alternating current (AC) power which is supplied to an inductive load by operation of an AC switch;
• detecting zero-voltage crossings of an AC voltage waveform of the AC power;
• generating a control signal to place a solid-state switch into a turned-off state;
• monitoring a load voltage of the inductive load to detect for a presence of inductive flyback voltage in the load voltage when the AC switch is placed into the turned-off state;
• and
• in response to detecting the presence of inductive flyback voltage in the load voltage, determine a delay time to place the AC switch into the turned-off state subsequent to a detected zero-voltage crossing of the AC voltage waveform, so that the AC switch placed into the turned-off state at a time which substantially coincides with a zero-current crossing of load current of the inductive load, to thereby suppress the generation of inductive flyback voltage when the AC switch is placed into the turned-off state.