Controllable-load circuit for use with a load control device

A load control system for controlling the amount of power delivered from an AC power source to an electrical load, the load control system comprising:

• a load control device adapted to be coupled to the electrical load for controlling the amount of power delivered to the electrical load;
• and
• a dimmer switch comprising a thyristor coupled in series electrical connection between the AC power source and the load control device, the thyristor characterized by a rated holding current and configured to conduct a load current from the AC power source to the load control device, the dimmer switch configured to generate a phase-control voltage that is provided to the load control device to enable the load control device to adjust the amount of power being delivered to the electrical load in response to a conduction period of the phase-control voltage;
• wherein the load control device is configured to conduct a controllable-load current from the AC power source through the thyristor of the dimmer switch, the load control device configured to maintain the magnitude of the controllable-load current constant for at least a portion of each half-cycle of the AC power source, the load control device configured to decrease the magnitude of the controllable-load current from an initial magnitude in a first half-cycle to a decreased magnitude in a second subsequent half-cycle, such that the decreased magnitude of the load current conducted through the thyristor in the second half-cycle exceeds the rated holding current.

A load control system for controlling the amount of power delivered from an AC power source to first and second electrical loads, the load control system comprising:

• a first load control device adapted to be coupled to the first electrical load for controlling the amount of power delivered to the first electrical load;
• a second load control device adapted to be coupled to the second electrical load for controlling the amount of power delivered to the second electrical load;
• and
• a dimmer switch comprising a thyristor coupled in series electrical connection between the AC power source and the first and second load control devices, the thyristor characterized by a rated holding current and configured to conduct a load current from the AC power source to the first and second load control devices, the dimmer switch configured to generate a phase-control voltage that is provided to the first and second load control device to enable the first and second load control devices to adjust the amount of power being delivered to the respective electrical loads in response to a conduction period of the phase-control voltage;
• wherein the load control devices are configured to conduct respective controllable-load currents from the AC power source through the thyristor of the dimmer switch, the load control devices configured to maintain the magnitude of each controllable-load current constant for at least a portion of each half-cycle of the AC power source, the load control devices each configured to adjust the magnitude of the respective controllable-load current from an initial magnitude in a first half-cycle to a decreased magnitude in a second subsequent half-cycle, such that a total magnitude of the respective controllable-load currents exceeds the rated holding current when the controllable-load currents have the respective decreased magnitudes in the second half-cycle.

A controllable-load circuit for drawing a selected current from a power source comprising:

• a first semiconductor switch having a control input coupled to the power source;
• a first impedance forming circuit connected in series with the first semiconductor switch across the power source, the first impedance forming circuit including a first input for selecting between at least two impedances to be connected in series with the first semiconductor switch;
• a control circuit having an output coupled to said first input for selecting the selected impedance;
• and
• a second circuit coupled to said first semiconductor switch for monitoring the power source and for increasing the impedance to current flowing from said power source through said first semiconductor switch at a selected voltage level of said power source, thereby to reduce the current through said first semiconductor switch;
• wherein said power source comprises an alternating current source, said control circuit configured to control the impedance of said impedance forming circuit to automatically control the current through said first semiconductor switch to be at a predefined level, said control circuit configured to control the impedance of said first impedance forming circuit for each half-cycle of the alternating current source;
• further wherein the controllable-load circuit is coupled across the power source providing power to a driver circuit driving an LED light source.

A controllable-load circuit for drawing a selected current from a power source comprising:

• a first semiconductor switch having a control input coupled to the power source;
• a first impedance forming circuit connected in series with the first semiconductor switch across the power source, the first impedance forming circuit including a first input for selecting between at least two impedances to be connected in series with the first semiconductor switch;
• a control circuit having an output coupled to said first input for selecting the selected impedance, said control circuit configured to control the impedance of said impedance forming circuit to automatically control the current through said first semiconductor switch to be at a predefined level;
• a second circuit coupled to said first semiconductor switch for monitoring the power source and for increasing the impedance to current flowing from said power source through said first semiconductor switch at a selected voltage level of said power source, thereby to reduce the current through said first semiconductor switch;
• wherein the power source comprises a source of rectified alternating current having a phase control component, the phase control component comprising one of a forward phase control component or a reverse phase control component, said control circuit configured to determine whether said rectified alternating current comprises a forward phase control component or a reverse phase control component, said control circuit further configured to render the first semiconductor switch conductive when there is a forward phase control component and to render the first semiconductor switch nonconductive when there is a reverse phase control component.

A load control device for controlling the amount of power delivered from an AC power source to an electrical load, the load control device adapted to be coupled to the AC power source through a dimmer switch, the load control device comprising:

• a load control circuit adapted to be coupled to the electrical load for controlling the amount of power delivered to the electrical load;
• a controller coupled to the load control circuit for controlling the amount of power delivered to the electrical load in response to a phase-control voltage received from the dimmer switch;
• and
• a controllable-load circuit coupled to the controller, the controllable-load circuit operable to conduct a controllable-load current from the AC power source through the dimmer switch;
• wherein the controller is operable to determine whether the phase-control voltage comprises a forward phase-control waveform or a reverse phase-control waveform, the controller operable to operate in a first mode when the phase-control voltage is a forward phase-control waveform, and to operate in a second mode when the phase-control voltage is a reverse phase-control waveform;
• wherein the controller is operable to enable the controllable-load circuit, such that the controllable-load circuit conducts the controllable load current through the dimmer switch when the controller is operating in the first mode, the controller further operable to disable the controllable-load circuit, such that the controllable-load circuit does not conduct the controllable-load current through the dimmer switch when the controller is operating in the second mode;
• and
• wherein a magnitude of the controllable load current conducted by the controllable-load circuit through the dimmer switch exceeds at least one of a rated latching current or a rated holding current of the dimmer switch.

An LED driver for controlling the amount of power delivered from an AC power source to an LED light source, the LED driver adapted to be coupled to the AC power source through a dimmer switch, the LED driver comprising:

• a bus capacitor for storing a DC bus voltage;
• an LED drive circuit coupled to the bus capacitor for receiving the DC bus voltage and adapted to be coupled to the LED light source for controlling the amount of power delivered to the LED light source;
• a controller coupled to the LED drive circuit for controlling the amount of power delivered to the LED light source to control the intensity of the LED light source in response to a phase-control voltage received from the dimmer switch;
• and
• a controllable-load circuit coupled to the controller, the controllable-load circuit operable to conduct a controllable-load current from the AC power source through the dimmer switch;
• wherein the controller is operable to determine whether the phase-control voltage comprises a forward phase-control waveform or a reverse phase-control waveform, the controller operable to enable the controllable-load circuit, such that the controllable-load circuit conducts the controllable-load current through the dimmer switch when the phase-control voltage is a forward phase-control waveform, the controller further operable to disable the controllable-load circuit, such that the controllable-load circuit does not conduct the controllable-load current through the dimmer switch when the phase-control voltage is a reverse phase-control waveform.