Abstract: A power converter and method for providing surge protection to the power converter is provided herein. An over voltage protection portion of a protection circuit is coupled between the rail voltage and ground reference of the power converter, and senses a first magnitude of the rail voltage. An under voltage protection portion of the protection circuit is coupled to a controller of the power converter and further between the rail voltage and the ground reference, and senses a second magnitude of the rail voltage to be transmitted to the controller. A regulator block is coupled between the over voltage protection portion and the under voltage protection portion, and is configured to compare the first magnitude of the rail voltage to a reference voltage of the regulator block, and to short circuit the under voltage protection portion when the first magnitude of the rail voltage is greater than the reference voltage.

Abstract: An electromagnetic interference (EMI) suppression circuit is interposed between an AC source and a DC power conversion system. The EMI suppression circuit includes a pi-type filter network having first and second filter input terminals and having first and second filter output terminals. The pi-type filter network includes a common mode choke and a differential mode choke between the input terminals and the output terminals. The pi-type filter network includes a first X-type capacitor across the first and second filter input terminals and includes a second X-type capacitor across the first and second filter output terminals. A first Y-type emission reduction capacitor is connected between the first filter input terminal and earth ground. At least a second Y-type emission reduction capacitor and a damping resistor are connected in series to form a series resistor-capacitor combination between the first filter output terminal and earth ground.

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: 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: 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 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 ballast configured for multiple parallel lamp operation includes a system for detecting unbalanced loads or absent lamps in a parallel multiple lamp ballast. The ballast includes one or more starting transformers having windings, each winding connected in series with a lamp connected to the ballast. A winding of one or more of the starting transformers that is not connected in series with one of the lamps is monitored for a voltage in excess of a threshold. A voltage in excess of the threshold across the winding is indicative of an unbalanced load (e.g., an absent or broken lamp). If a voltage above the threshold is detected across the monitored load, the ballast ceases powering the lamps.

Abstract: A high efficiency electronic ballast or driver circuit provides striation control at reduced power levels. The driver circuit includes a controller operating a half-bridge inverter to drive a resonant tank circuit. The controller provides asymmetric on-times to upper and lower switches of the half-bridge inverter when operating at low duty cycles (e.g., duty cycles of 50% or less). The resulting asymmetric output current eliminates striation in lamps driven by the ballast. In order to maintain light output (i.e., output current), the controller reduces the operating frequency of the half-bridge inverter to increase the gain and impedance of the resonant 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.

Abstract: A power line communication system communicates a ballast dimming level to an electronic ballast over an AC power line. A power line controller is operable to generate the ballast control signal and to insert that signal on the AC power signal being transmitted over the AC power line. A power line receiver receives the AC power signal and extracts the ballast control signal from the AC power signal to generate the dimming level signal corresponding with the desired ballast dimming level. To insert the ballast control signal on the AC power signal, the power line controller has a transformer coupled to the signal pattern circuit. The secondary winding of this transformer is connected in series with the AC power line to insert the ballast control signal on the AC power signal. This AC power signal is then transmitted to the electronic ballast. To extract the ballast control signal out of the AC power signal, the power line receiver has a resonant circuit connected in series with the AC power line.

Abstract: The present invention is an overvoltage protection and automatic re-strike circuit for an electronic ballast. The electronic ballast has an inverter, a shut-down circuit, a safety circuit, a monitoring circuit, and an overvoltage protection circuit. The inverter provides an appropriate alternating current power supply to operate the lamp. The shut-down, safety, monitoring, and overvoltage protection circuits are coupled to the inverter and provide the overvoltage protection and automatic re-striking functions. During an overvoltage condition, the overvoltage protection circuit will temporarily disable the inverter. Subsequent to the overvoltage condition, the overvoltage protection circuit permits the inverter to attempt to re-ignite the lamp. After a predetermined number of unsuccessful re-ignition attempts, the safety circuit will permanently disable the inverter to avoid damage to the ballast.