Our patent is a system and method for controlling the power delivered to a load by an alternating current (AC) electrical circuit having a line voltage. Root Mean Square (RMS) voltage is a measure of the average power. The RMS voltage is reduced by disconnecting the power line for a short interval (0.008 seconds for 60 Hz US power systems). The number of disconnects per second determines the average power consumed and therefore the RMS voltage. Different RMS voltages can be achieved by controlling the number of disconnects per second.
A unique feature of the patent is that the disconnect occurs when the stored energy is zero. For the common case of inductive and resistive loads, the energy stored in the load is zero when the current is zero. For these cases the disconnect begins when the current is zero. Power is reapplied when the voltage is zero. Disconnections alternate between removing positive voltage half-cycles and negative voltage half-cycles to avoid a direct current (DC) bias. A system incorporating digital logic elements is provided for implementing the method and for detecting whether the load is inductive or capacitive.
Spikes of voltage that produce radio frequency interference (RFI) are avoided by switching power off when the stored energy is zero.
This method can be implemented using a small, inexpensive circuit.
The patent also describes logic to determine if the load is capacitive or inductive.