Abstract: A lighting device, and method of controlling a power stage thereof, is provided to stabilize operation at low output currents. An output current is sensed as a feedback signal and provided to control circuitry, which further defines upper and lower boundaries for a control band about an average sensed input control value. A reference signal corresponds to the average sensed input control value, wherein adjustments to the reference signal are enabled only when an actual sensed input control value extends beyond the control band. The upper and lower boundaries may be linearly or non-linearly approaching the average control value as a function of increases in the average control value, to prevent control adjustments in particular for low output current conditions. Control signals are generated for driving one or more switching elements in the power stage, based at least in part on the feedback signal and the generated reference signal.

Abstract: A driver circuit provides current to a light source from a resonant tank having a single inductive element. The driver circuit is coupled to DC power source having a power rail and a ground, and includes a power inverter providing AC input to the tank, which further includes a DC blocking capacitor and a primary winding of the inductive element coupled in series between the output of the inverter and the ground. A leakage inductance of the inductive element provides resonant inductance for the tank. The inductive element further distributes power output from the resonant tank to a plurality of secondary windings coupled to an output rectifier. A resonant capacitor coupled across output ends of the secondary windings provides resonant capacitance for the tank. The output voltages across the secondary windings are clamped to a value based in part on a turns ratio between respective secondary windings.

Abstract: A magnetic assembly includes a single bobbin structure that supports a first coil and a second coil. A first E-core has a center leg positioned within the first coil. A second E-core has a center leg positioned within the second coil. An I-core is positioned between the first E-core and the second E-core. The I-core completes a first set of magnetic paths between the center leg and outer legs of the first E-core and also completes a second set of magnetic paths between the center leg and outer legs of the second E-core. The two E-cores and the I-core are stacked in a vertical E-I-E configuration with respect to a common set of pin rails. In one embodiment, the first coil and the first E-core are configured as a transformer; and the second coil and the second E-core are configured as an inductor.

Abstract: An adjustable auxiliary power supply for a light emitting diode (LED) driver for adjusting an auxiliary power output includes a voltage regulator configured to receive a regulator input voltage and to output an auxiliary power supply voltage selected from a first output voltage and a second output voltage according to a voltage selection signal used to control an LED lighting setting. The adjustable auxiliary power supply includes a first and second input voltage circuits configured to selectively output respective first and second input voltages to the voltage regulator. The adjustable auxiliary power supply includes an adjustable resistance circuit coupled to the voltage regulator. The adjustable resistance circuit controls the auxiliary power supply voltage based upon an adjustable resistance setting of the adjustable resistance circuit. The adjustable resistance setting is configured to correspond to at least one of the first output voltage and the second output voltage.

Abstract: An LED driver is provided with transient protection circuitry to satisfy dielectric testing requirements. An embodiment of the driver includes a fuse coupled between an AC input and a DC power source, and first and second electrolytic capacitors coupled across the DC power source. Respective circuits including a transient voltage suppressor and a current limiting resistor are coupled in series across each of the electrolytic capacitors. The transient voltage suppressors have breakdown voltage thresholds slightly below a full rated output for the DC source, wherein a sensed short condition across one of the first and second electrolytic capacitors causes a short circuit across the DC source and thereby disabling of the LED driver prior to failure of the other electrolytic capacitor. The current limiting resistors further are configured to avoid causing the LED driver to be disabled for transient overvoltage conditions in which neither of the electrolytic capacitors is shorted.

Abstract: A DC-to-AC inverter provides power to a DC-to-AC converter via an isolation transformer. The DC-to-AC converter drives a DC load. A sensing circuit on the primary side of the isolation transformer senses the current flowing through the primary winding of the transformer. A capacitor is connected across the primary winding in parallel with the magnetizing inductance of the primary winding to form a parallel L-C combination. The capacitance of the capacitor is selected with respect to the magnetizing inductance such that the parallel L-C combination resonates at a nominal steady-state operating frequency of the DC-to-AC inverter, which causes the current through the primary winding to be proportional to a current through the DC load. The current through the primary winding is sensed and provided as a feedback signal to the DC-to-AC inverter to cause the DC-to-AC inverter to adjust the operating frequency to maintain the current at a desired magnitude.

Abstract: An LED driver circuit and a method prevent LED turn-off flash when input power is lost to the driver circuit. The driver circuit includes a DC-DC converter that provides an LED drive voltage to an LED load. A voltage drop sensing circuit detects the loss of input power and discharges a filter capacitor that provides operating power to a controller in a DC-DC converter. The controller turns off to halt the operation of the DC-DC converter before the voltage provided to the LED load decreases to a turn-off threshold of the LED load. The DC-DC converter cannot recharge a load capacitor across the LED load. Thus, once the LEDs in the LED load turn off, the LEDs remain off until the input power is restored.

Abstract: An LED driver circuit is provided with a dynamic operating range which can be set using an offline tuning interface. During an offline mode of operation, the tuning interface may be coupled to the dimming control interface and provide both power and one or more digital pulses corresponding to a desired maximum output voltage and/or maximum output current. The controller then modifies the programmed maximum output voltage and the maximum output current values based on the one or more digital pulses received via the tuning interface circuit. Group tuning is permitted by way of a shared bus between a programming device and a plurality of LED driver circuits. Tuning confirmation or error may be detected by an LED driver circuit and the programming device may be notified of the success or failure of a particular tuning operation.

Abstract: An LED driver circuit is provided with a dynamic operating range which can be set using an offline tuning interface. During an online mode of operation, a controller for a power converter is configured to regulate the output voltage and the output current generated by the power converter based on a dimming control signal from a dimming control interface, a sensed output from the power converter, and programmed maximum output voltage and maximum output current values. During an offline mode of operation, the tuning interface may be coupled to the dimming control interface and provides a sequence of digital pulses corresponding to a desired maximum output voltage, maximum output current, or operating parameter. The controller then modifies the programmed maximum output voltage and the maximum output current values based on the predetermined sequence of digital pulses received via the tuning interface circuit.

Abstract: An LED driver is provided with input surge absorbing capacity. A surge protection circuit branch is coupled across output lines from a DC power source, in parallel with and between a filtering capacitor and a non-isolated buck-boost PFC circuit. A variable impedance device such as a spark gap is coupled to a first power line and having a breakdown voltage to operate as an open circuit during normal operating conditions with respect to a peak input voltage across the capacitor. Responsive to a surge condition with respect to excess energy across the capacitor, the spark gap operates as a closed circuit, and a second capacitor coupled between the spark gap and the second line absorbs the excess energy. Responsive to a return to normal operating conditions, the spark gap reverts to an open state and the accumulated surge energy is discharged from the second capacitor to circuit ground.

Abstract: An LED driver provides constant output power with wide range output current and voltage. A parallel resonant tank configuration is supplemented by resonant gain clamping circuit configured to partially cancel voltage across the resonant capacitor during half-bridge switching operation. Voltage between the resonant components is clamped to one-half a driver input voltage, ensuring inductive switching of the half-bridge. An output transformer has a primary winding coupled across the resonant capacitor, with a center tap defining first and second portions. An output voltage clamping circuit is coupled across the DC input power source and to the center tap, wherein maximum voltage across the primary is clamped based on a relationship between respective numbers of turns in the first and second portions, and maximum voltage across a secondary winding is clamped based on a relationship between the respective numbers of turns in the secondary winding and the first and second portions.

Abstract: A floating output power supply includes circuitry for indirectly sensing an output current and output voltage of the floating output power supply. The circuitry includes a circuit ground referenced current sensing resistor placed in between diodes forming one leg of a full wave rectifier. The voltage of this current sensing resistor is circuit ground referenced and representative of an output current of the floating output power supply. A resistive network is coupled between a negative output and a positive output of the floating output power supply. The resistive network includes a circuit ground referenced resistor whose voltage is representative of the output voltage of the floating output power supply. A controller of the floating output power supply determines output voltage, current, and/or power from these sensed voltages and currents and adjusts an operating parameter of an input power supply as a function of the determined output voltage, current, and/or power.

Abstract: A power factor correction (PFC) circuit includes an adaptive multiplier feedback control circuit to enhance stability of the PFC circuit for high input voltage and low input power (i.e., low input current) conditions. The adaptive multiplier feedback control circuit controls a voltage provided to a multiplier voltage input of a controller of the PFC circuit. The controller determines control loop gain as a function of the voltage at the multiplier voltage input terminal of the controller. The adaptive multiplier feedback control circuit increases the voltage at the multiplier voltage input of the controller is the input current to the PFC circuit increases. The PFC circuit may be used in an AC to DC converter of the driver circuit of a light fixture operable to provide power to a light source of the light fixture.

Abstract: A constant current source has an increased differential amplifier gain at low output currents and a decreased differential amplifier gain at high output currents. The differential amplifier amplifies a sensed output current of the constant current source. A gain control circuit scales a reference current in conjunction with the gain applied to the sensed output current to maintain stable operation of the constant current source. The constant current source may be used in a driver circuit to provide power to a light source (e.g., an LED light).

Abstract: A constant current driver circuit is operable to provide power to a light source. The driver circuit utilizes a microcontroller based oscillator to drive a current source tank circuit. The microcontroller based oscillator is controlled by a differential error feedback signal. The differential error feedback signal is produced by a proportional integral control loop. The proportional integral control loop is used to eliminate steady state error of the driver circuit. Dynamic frequency or duty cycle control of the current source tank circuit by the microcontroller is based on the integrated error signal between a reference current signal and a sensed output current of the current source tank circuit.

Abstract: A ballast is designed to adaptively warm-up one or more lamps driven by the ballast when the lamps are dimmed to a selected dimming level and lamp impedance instability results. The ballast can therefore maintain a stable light output in low ambient temperature conditions that normally cause lamp impedance instability and visible flickering of the lamp. The ballast uses lamp impedance sensing circuit to sense lamp instability and adaptively warms up the lamp whenever the ballast detects lamp instability by increasing the current provided to the lamp (i.e., current through the lamp) for a predetermined period of time.

Abstract: A lighting ballast and associated methods balance current through resonant inductors that have inductance variation, and are further effective to balance lamp currents in the range from full brightness to full dimming. The ballast includes a lighting power source, a balancing transformer having a plurality of windings, a first resonant tank circuit having one or more transformer windings and a second resonant tank circuit having a like number of transformer windings. Each of the windings for the first resonant tank are reversed in direction in association with a corresponding winding for the second resonant tank, such that the only current passing through the windings is a current difference between the two windings.

Abstract: An electronic ballast is provided with circuitry for detecting the removal of one or more lamp filaments across a range of dimming levels, and regulating an output stage including at least first and second pairs of lamp connection output terminals based on a filament connection status. A filament removal sensing circuit is coupled to the output terminal pairs and configured to generate an output voltage representative of a filament connection status with respect to the output terminal pairs. A microcontroller is coupled to receive the output voltage from the filament removal sensing circuit and programmed to determine a rate of change in the output voltage, compare the rate of change in the output voltage to a predetermined threshold value, and disable the output stage when the rate of change in the output voltage exceeds the predetermined threshold value.