Method of soft-starting a switching power supply containing phase-control clipping circuit
View Patent ↗A method of operating a power controller that converts a line voltage to an RMS load voltage includes a soft start in which a conduction angle of a phase-control clipping circuit is gradually increased to a steady state value that defines the RMS load voltage. The controller has a circuit with a time-based signal source that triggers conduction independently of line voltage magnitude and a transistor switch whose gate receives signals from the time-based signal source to trigger the circuit. When starting the power controller, a microcontroller increases the conduction angle of the phase-control clipping circuit in plural steps to provide the soft start.
1. A method of operating a power controller that converts a line voltage to an RMS load voltage and that has a phase-control clipping circuit that clips a load voltage to define a conduction angle that sets the RMS load voltage, the circuit including a time-based signal source that sends signals to trigger conduction in the circuit independently of line voltage magnitude and a transistor switch whose gate receives the signals from the time-based signal source, the method comprising the steps of:
when starting the power controller, increasing the conduction angle of the phase-control clipping circuit, the conduction angle increasing in plural steps from a first value to a steady state value; and
during subsequent operation of the power controller, sending the signals from the time-based signal source with the steady state value of the conduction angle at constant time intervals to the gate of the transistor switch to cause the power controller to provide the RMS load voltage independently of line voltage magnitude.
2. The method of claim 1 , wherein the clipping circuit clips the load voltage immediately following each polarity change of the load voltage.
3. The method of claim 1 , wherein the clipping circuit clips the load voltage immediately before each polarity change of the load voltage.
4. The method of claim 1 , wherein the clipping circuit clips the load voltage in portions of cycles of the load voltage that include a peak value between adjacent polarity changes of the load voltage, and wherein the conduction angle spans from before to after polarity changes of the load voltage.
5. The method of claim 1 , wherein the clipping circuit includes a microcontroller that sets the conduction angle by controlling timing of the signals from the time-based signal source and the method further comprises the step of a user selecting in the microcontroller at least one of a location and range of the conduction angle.
6. The method of claim 1 , wherein the step of increasing the conduction angle of the phase-control clipping circuit comprises the step of increasing the conduction angle in each of plural consecutive cycles of the load voltage.