Abstract: A circuit for driving a load. In one embodiment, the load is driven by an inverter circuit having a full bridge circuit divided by inductive elements to provide cross conduction protection. In another embodiment, first and second converter circuits are coupled to the inverter circuit with the inverter and converter circuits having common circuit elements. In a further embodiment, a common mode inducter is inductively coupled to a power circuit for detecting a common mode signal generated by a load current return path disruption. The common mode inductor is coupled to a control circuit for limiting current to the load.

Abstract: An electronic circuit providing independent operation and application of instant start voltages to each of a plurality of lamps. In a first embodiment, a circuit includes inductively coupled first and second inductive elements disposed on a single bobbin. A capacitive element is coupled between the first and second inductive elements to allow the inductively coupled inductive elements to operate independently when a lamp is removed from the circuit. A steady state strike voltage is generated at the lamp terminals from which a lamp has been removed. In another embodiment, a circuit includes a first circuit path including a first inductive element coupled to a first lamp and a second circuit including a second inductive element coupled to a second lamp. The first and second inductive elements are inductively coupled to effectively cancel flux generated while the first and second lamps are energized.

Abstract: A ballast circuit independently energizes first and second lamps. In one embodiment, an inverter provides a drive signal for energizing the first and second lamps. A first signal detection circuit detects a first AC input signal and a second signal detection circuit detects a second AC input signal, each of which energizes a respective one of first and second lamps. A first lamp control circuit receives a signal from the first signal detector such that the first lamp is energized by the drive signal when the first AC input signal is present. Similarly, a second lamp control circuit receives a signal from the second signal detector such that the second lamp is energized by the drive signal when the second AC input signal is present.

Abstract: A ballast includes a hot restart circuit for hot restart of a HID lamp. In one embodiment, the hot restart circuit includes inductively coupled first and second inductive elements coupled end to end. A first capacitor has a first terminal coupled to a point between the first and second inductive elements and a second terminal coupled to a switching element. When the switching element transitions to a conductive state, a voltage pulse is generated on the second inductive element and the corresponding pulse on the first inductive element is sufficient to achieve hot restart of the lamp. In one embodiment, the first capacitor and the second inductive provide a parallel resonant LC circuit. The resultant signal on the second inductive element increases a voltage on the first inductive element for hot restart of the lamp.

Abstract: A ballast circuit for energizing a lamp includes an inverter circuit with a start up circuit which provides a repeating start up sequence until a lamp lights. The start up circuit includes a start up switching element coupled across a start up capacitor which initiates operation of the inverter. A rapid start capacitor is charged as the inverter applies a signal to the lamp and the voltage on the rapid start capacitor determines the conduction state of the start up switching element. The inverter applies an increasing strike voltage to the lamp until the lamp lights or until the lamp voltage becomes greater than a predetermined level. After the restart capacitor discharges, the start up capacitor charges to re-initiate operation of the inverter. The ballast thereby applies a strike voltage to the lamp having a relatively small duty cycle for reduced stress on the circuit components.

Abstract: A ballast circuit for energizing a lamp includes an inductive element coupled to an input terminal and a capacitive element coupled to the inductive element in parallel with the lamp. In one embodiment, the capacitive element includes a plurality of capacitors each of which is coupled in series with a switch to control the total capacitance provided by the capacitors. By controlling the total capacitance, the intensity of light emitted by the lamp can be selected. In another embodiment, a switching element is coupled across one of the capacitors for providing a selected capacitance to the circuit for controlling the lamp light intensity. In a further embodiment, a transformer has a first winding coupled in series with the capacitive element with the inductive impedance of the first winding being controlled via a second transformer winding coupled to a control circuit.

Abstract: A ballast circuit for energizing a lamp comprises a circuit for limiting and/or regulating signal levels to the lamp. In one embodiment, the ballast comprises a control circuit which regulates the lamp current to a predetermined level such that the ballast can drive lamps having a predetermined diameter, which determines the operating current, and having a length that can vary, which determines the voltage drop across the lamp. In another embodiment, the ballast comprises a threshold circuit for limiting a load current prior to striking the lamp as well as after the lamp conducts current.

Abstract: A ballast circuit for energizing a lamp includes an inverter circuit having a switching element with a conduction state controlled by a control circuit which limits a voltage applied to the lamp. In one embodiment, the control circuit includes an integrated circuit providing a conduction control signal to a duty cycle control circuit. The conduction control signal alternately biases the switching element to conductive and non-conductive states at a first duty cycle when the lamp voltage is below a predetermined level. When the lamp voltage becomes greater than the predetermined level, the duty cycle control circuit decreases the switching element to a second duty cycle, which is less than the first duty cycle, to reduce the voltage at the lamp. In one embodiment, the ballast regulates the lamp current to a predetermined level such that the ballast can energize a lamp which can vary in length and has a predetermined diameter.

Abstract: A HID ballast includes a control circuit that minimizes arc instability associated with acoustic resonance of a lamp energized by the ballast. In one embodiment, the ballast includes an inverter circuit having first and second switching elements coupled in a half bridge configuration. A first control circuit controls the conduction state of the first switching element and a second control circuit controls the conduction state of the second switching element. The second control circuit includes a limiting circuit that limits the pre- and post-ignition energy levels to the lamp. One feature of the invention limits the lamp current amplitude such that the lamp can be driven while in acoustic resonance. In another embodiment, the inverter circuit includes a resonant inductive element and a resonant capacitive element which is coupled in parallel with the lamp.

Abstract: A ballast circuit includes a rectifier for coupling to independent first and second AC input signals, a first inverter for energizing a first lamp and a second inverter for energizing a second lamp. A boost converter can be coupled between the rectifier and the inverters. The first inverter is enabled when the first AC input signal is applied to the rectifier and the second inverter is enabled when the second AC input signal is present.

Abstract: A ballast includes a resonant inverter circuit which limits the voltage applied to a lamp when it fails to light. In one embodiment, the inverter includes first and second switching element having conduction states controlled by respective first and second control circuits. The second control circuit includes a third switching element which controls the conduction state of the second switching element. An end of life circuit includes a first threshold circuit coupled to the third switching element for disabling the inverter when the voltage applied to the lamp becomes greater than a first predetermined threshold. In another embodiment, the second control circuit includes a fourth switching element for controlling a duty cycle of the third switching element and the end of life circuit includes a second threshold circuit. When the lamp voltage becomes greater than a second predetermined threshold, the fourth switching element reduces the duty cycle of the third switching element.

Abstract: A circuit having a full bridge configuration with a single actively biased switching element. In one embodiment, the circuit is a ballast circuit having a full bridge inverter with one switching element. The bridge includes a diode coupled to the switching element such that the diode and the switching element are coupled between positive and negative rails of the inverter. The bridge further includes first and second capacitors coupled end to end across the positive and negative rails. The ballast circuit can be coupled to a rectifier/boost circuit having a boost inductor coupled to the inverter circuit.

Abstract: A circuit for energizing a load includes an inverter which provides a feedback signal to a rectifier for substantially linear operation of the rectifying diodes. In one embodiment, a ballast includes a rectifier and a resonant inverter which energizes a lamp. The inverter generates a current that is split between a first path which includes the lamp and a second path which includes a feedback capacitor. A feedback path, which includes a feedback inductor, extends from the feedback capacitor to a point between the rectifying diodes. The feedback capacitor and feedback inductor resonate in series to provide a reactive feedback signal for achieving substantially linear operation of the diodes. In another embodiment, the lamp current flows to a clamp circuit for limiting the lamp current to a predetermined level.

Abstract: A circuit, such as a ballast circuit, includes a resonant feedback signal from an inverter that provides substantially linear operation of rectifying diodes. In one embodiment, capacitors coupled in series with respective lamps resonate with a first winding of a feedback transformer so as to generate a feedback signal on a second winding of the transformer. The feedback signal is effective to produce substantially linear operation of the rectifying diodes.

Abstract: An electronic circuit includes first and second inductive bias elements coupled to respective first and second switching elements for preventing avalanche current flow through the switching elements. In one embodiment, a resonant inverter circuit includes first and second switching elements with first and second freewheeling diodes coupled across the respective switching elements. A first inductive bias element is coupled to the first switching element and a second inductive bias element is coupled to the second switching element. The first and second bias elements are inductively coupled with a resonant inductive element for biasing the respective first and second switching elements against avalanche current flow.

Abstract: An electronic circuit providing independent operation and application of instant start voltages to each of a plurality of lamps. In a first embodiment, a circuit includes inductively coupled first and second inductive elements disposed on a single bobbin. A capacitive element is coupled between the first and second inductive elements to allow the inductively coupled inductive elements to operate independently when a lamp is removed from the circuit. A steady state strike voltage is generated at the lamp terminals from which a lamp has been removed. In another embodiment, a circuit includes a first circuit path including a first inductive element coupled to a first lamp and a second circuit including a second inductive element coupled to a second lamp. The first and second inductive elements are inductively coupled to effectively cancel flux generated while the first and second lamps are energized.

Abstract: A circuit including a rectifier having rectifying diodes has a feedback signal which provides substantially linear operation of the rectifying diodes. In one embodiment, a ballast circuit includes a rectifier circuit coupled to an inverter circuit which energizes a fluorescent lamp. The inverter circuit includes a ballast capacitor coupled to an inductive feedback element. The voltages generated across the ballast capacitor and the feedback element combine to provide a feedback signal that is effective to periodically bias at least one of the rectifying diodes to a conductive state during substantially the entire AC input signal. The substantially linear operation of the rectifying diodes enhances THD and PF performance of the circuit.

Abstract: A circuit for driving a load. In one embodiment, the load is driven by an inverter circuit having a full bridge circuit divided by inductive elements to provide cross conduction protection. In another embodiment, first and second converter circuits are coupled to the inverter circuit with the inverter and converter circuits having common circuit elements. In a further embodiment, a common mode inductor is inductively coupled to a power circuit for detecting a common mode signal generated by a load current return path disruption. The common mode inductor is coupled to a control circuit for limiting current to the load.

Abstract: A method and apparatus for efficiently driving a load coupled to a ballast is described. A switching element coupled between a pair of ballast terminals converts a low frequency drive signal to a high frequency drive signal which is provided to the load.