Abstract: There is provided a backlight unit driver capable of driving multi-channel lamps of a backlight unit, especially LED lamps, by supplying a driving power to the lamps using a single transformer and maintaining the current balance of the driving power supplied to each of the lamps.

Abstract: There are provided a current balance circuit having a protection function that prevents the current balance circuit from being damaged during a preset time period by maintaining a constant level of power being supplied to the lamp, and a power supply. The current balance circuit having the protection function includes a current balance unit maintaining current balance of lamp driving power supplied to a lamp unit including a plurality of lamps, and a protection unit detecting the lamp driving power supplied to the lamp unit from the current balance unit, cutting-off the lamp driving power after a preset time period when the lamp operates abnormally, and controlling a voltage level of the lamp driving power to a preset reference voltage level or lower during the preset time period.

Abstract: A lighting device may include a transformer; a rail device, configured to be attached to a surface of an object, wherein the rail device has two rails, which are arranged so as to be spaced apart from one another, to which rail device a lamp can be attached and on which the lamp can be supplied with power, the rails being electrically connected to the transformer, at least one first lamp being arranged on the rails and being configured to be supplied with power in the low-voltage range via the transformer and the rails; and at least one second lamp being arranged on a housing of the transformer and being connected to the system voltage.

Abstract: An ignition transformer for a discharge lamp is provided having a transformer core whose material and dimensions are selected in such a manner that the Curie temperature of the material after the ignition which is achieved by means of the ignition transformer can be achieved by a voltage drop across a secondary winding of the ignition transformer.

Abstract: An inrush current limiter for use with an LED driver including a current limiting device, a bypass switch device, and a switch drive. The current limiting device is placed in the input current path of the LED driver to limit input current to a predetermined maximum level in response to an AC conductive angle modulated voltage. The bypass switch device is coupled in parallel with the current limit device. The switch drive turns on the bypass switch device to at least partially bypass the current limiting device as a voltage level of an input of a switching converter rises. The input current remains sufficiently high without exceeding the maximum level. The switch drive is implemented with a delay network driven either by a separate transformer winding or by a snubber network. The delay network may have a delay based on the delay caused by the current limiting device.

Abstract: A power supply unit with a dimming function which is adapted for a light emitting apparatus including a power system is provided. The power supply unit includes at least one output channel, a power stage, a detecting unit, and a micro controller unit (MCU). The power stage receives a first output of the power system and provides a first signal. The detecting unit detects a second output of the power system and provides a second signal. The MCU receives the first signal and the second signal, controls the at least one output channel, and is programmed to set a dimming ratio for the at least one output channel according to the first signal and the second signal. Furthermore, a light emitting apparatus and a dimming method are also provided.

Abstract: A multi-lamp driving system includes a power supply and at least one balance transformer. Each balance transformer includes two cores, two primary windings, two secondary windings and two protection windings. Each primary winding is wrapped around a core and serially connected to a lamp to form a first circuit branch in parallel connection with each other. The first circuit branches are powered by the power supply. The Each secondary winding is wrapped around a core and connected to a primary winding. The two secondary windings are connected in series to form a short circuit loop. Each of the protection windings is wrapped around a core and connected to a primary winding. The protection windings are wrapped in opposite directions and connected in series to form a second circuit branch. The second circuit branch outputs voltage signals to the power supply when induced voltages crossing the protection windings are unequal.

Abstract: Power consumed by an LED driver may be reduced by drawing, from an electronic transformer or dimmer, an input current that is constant over a plurality of input voltages. Power derived from the constant input current is provided to the LED driver.

Abstract: A process for controlling a brightness of a lamp includes, in at least one aspect, detecting input to control a brightness of a fluorescent lamp operated by a driving signal, and in response to detecting the input, modifying the driving signal to control the brightness of the fluorescent lamp, wherein modifying the driving signal comprises alternately applying a first duty cycle and a second duty cycle to the driving signal, wherein the first duty cycle and the second duty cycle are substantially complementary to each other.

Abstract: A driving device for a lamp, in particular an HID lamp, the device including a first circuit to convert a network input voltage into a output direct voltage, a second circuit that receives the direct voltage as an input and converts the direct voltage into an alternating signal for supplying the lamp. The first circuit includes a transformer provided with a secondary winding elements a center tap. The driving device further includes at least two capacitive elements connected to the center tap of the secondary winding of the transformer and coupled with the ends of the secondary winding and with the input of the second circuit.

Abstract: A method for operating a switching power supply is provided. A switching element is switched on and off by a switching signal with a variable switching frequency. A frequency bandwidth is predefined for determining average levels of a frequency spectrum of the switching signal. The switching frequency is modulated by a modulation frequency greater than a frequency bandwidth.

Abstract: A method and apparatus for reducing unwanted radiation from a light fixture have been disclosed.

Abstract: An electronic ballast is provided for powering one or more discharge lamps independently connected in parallel. An inverter having a pair of switching elements converts a DC supply signal into AC power. A transformer has a primary winding coupled to an output terminal of the inverter. A load circuit includes independently operable discharge lamp circuits coupled in parallel with each other and across a secondary winding of the transformer. An inductance control circuit includes an inductive element coupled in series with the primary winding of the transformer and a bi-directional switch coupled in parallel across the inductive element. A switch state of the bi-directional switch is controllably adjustable between first and second switch states and in accordance with a desired duty ratio. A magnitude of a voltage across the secondary winding of the transformer and thereby across each lamp circuit is dependent on the switch state of the bi-directional switch.

Abstract: An optical reactor has a reactor enclosure defining a reaction chamber. In the reaction chamber, a light source operating at a very high frequency is arranged to radiate light to a fluid to be treated. A low voltage electrode is arranged to surround the light source. The light source is energized by a driving circuit which is arranged adjacent to the reactor enclosure. The driving circuit has a high voltage output terminal connected to a high voltage input terminal of the light source. The driving circuit has a low voltage output terminal which is connected to the low voltage electrode.

Abstract: An active type multiple channeled LED power driving system which includes seven regions, wherein power is lead-in through the first region with the EMC circuitry and the PWM circuitry, passing through the second region with the transformer, entering the third region with the CC & CV control circuitry, passing through the fourth region with two multiple channeled outputers, lead-in the fifth region having two intermittent modulating circuitries, outputting to the sixth region with the two LED lighting modules, and setting with environment parameters sensors in the seventh region, thereby raising the electronic typed heat dissipation rate and energy efficiency under the system operation to let the LED lamp be able to achieve its maximum performance.

Abstract: A lighting device (8) including a cold-cathode fluorescent tube (light source) (9) includes an inverter circuit (16) connected to the cold-cathode fluorescent tube (9) and configured so as to driving the cold-cathode fluorescent tube (9), using PWM dimming. The inverter circuit (16) drives the cold-cathode fluorescent tube (9) while a dimming signal in the PWM dimming and a driving signal for driving the cold-cathode fluorescent tube (9) are synchronized.

Abstract: Disclosed is a lamp-tube driving device including a controller, an oscillating circuit, a converter, and a protective circuit. Connection relations there-between include the oscillating circuit coupled to the controller, the converter coupled to the controller and CCFL, and the protective circuit coupled to the CCFL and oscillating circuit. The controller is activated in response to first input voltage, and configured to output a control signal in response to second input voltage. The oscillating circuit is able to adjust oscillating frequency of operation clock for the controller. The converter is controlled with the control signal, and configured to convert third input voltage into an output voltage. This output voltage is for driving the CCFL. The protective circuit disables the oscillating circuit when the CCFL remains at a state such as open circuit or short circuit. A lamp-tube module and a lamp-tube driving system for the lamp-tube driving device are further disclosed.

Abstract: A power conversion controller having an adaptive peak current reference, including: a peak current reference generation means, used for generating a peak current reference signal by performing an adaptive arithmetic operation on an output voltage feedback signal and a power source signal; and a comparator means, used for generating a gating signal by performing a voltage comparison operation on the peak current reference signal and a current sensing signal.

Abstract: An apparatus, method and system are disclosed for supplying power to a load such as a plurality of light emitting diodes. A representative apparatus comprises a primary module, a first secondary module couplable to a first load, and a second secondary module couplable to a second load. The primary module comprises a transformer having a transformer primary. The first secondary module comprises a first transformer secondary magnetically coupled to the transformer primary, and the second secondary module comprises a second transformer secondary magnetically coupled to the transformer primary, with the second secondary module couplable in series through the first or second load to the first secondary module.

Abstract: An electronic control gear for a HID lamp receives an input signal for operating the lamp and frequency modulates the input signal to generate a frequency modulated output signal that drives an arc of the lamp. The frequency modulation of the output signal sweeps continuously between a low frequency modulation and a high frequency modulation, the low frequency modulation being a frequency f1 in a range of 125 kHz to 150 kHz and the high frequency modulation being a frequency f2 in a range of 230 kHz to 300 kHz, where f2?f1 is at least 0.4*f1. A power amplifier changes an amplitude of the frequency modulated output signal during the low frequency modulations so that a current amplitude of the frequency modulated output signal is substantially constant, and a variable gain transformer adjusts a voltage of the frequency modulated output signal during starting of the lamp.

Abstract: The present invention relates to a new discharge element having a discharge-control electrode for inducing a discharge even at low voltage by improving a characteristic in which a discharge element may not be discharged against a fast transient voltage when it is at low voltage, and more specifically, the discharge element having a discharge-control electrode according to the present invention comprises an airtight cylinder formed with a ceramic insulation material, a pair of discharge electrodes arranged for facing an end opening of the airtight cylinder, a discharge gap formed between the pair of discharge electrodes, a discharge-assisting material filled inside the airtight cylinder, and a discharge-control electrode in contact with the airtight cylinder and physically separated from the discharge-assisting material, wherein a discharge between the pair of discharge electrodes is induced by a control voltage applied through the discharge-control electrode.

Abstract: A group of novel power conversion concept is developed with this invention for LED and OLED drive applications. The concept utilizes a single power conversion stage to fulfill multiple functions, including Power Factor Correction, DC voltage to DC current conversion, or DC voltage to DC voltage conversion etc. that are necessary for driving LED devices from an AC power input. Multiple dimming control schemes have also been developed to facilitate wide range of application requirements and enable the system to work with different input power format including AC mains power and variable AC voltage from the existing AC dimmer installations.

Abstract: A ring balancer comprising a plurality of balancing transformers facilitates current sharing in a multi-lamp backlight system. The balancing transformers have respective primary windings separately coupled in series with designated lamps and have respective secondary windings coupled together in a closed loop. The secondary windings conduct a common current and the respective primary windings conduct proportional currents to balance currents among the lamps. The ring balancer facilitates automatic lamp striking and the lamps can be advantageously driven by a common voltage source.

Abstract: A circuit arrangement for starting and for operating a gas discharge lamp with an AC step-down converter or a half-bridge arrangement, which functions as a step-down inverter during quasi-resonant operation, a lamp inductor and a resonant capacitor, which form a resonant circuit, and a smoothing inductor, wherein the resonant capacitor is dimensioned in terms of its value such that, during normal operation of the lamp, a voltage ripple of over 100 V from maximum to maximum is present across said resonant capacitor, the smoothing inductor being dimensioned in such a way that it can filter the majority of the voltage ripple, and the switching frequency at the same time being between 200 kHz and 500 kHz.

Abstract: An illumination device (1) comprises: at least one low-power light source (50); a power input stage (20) suitable for receiving AC low voltage from an electronic transformer (ET); a power buffer stage (30) having an input (31) connected to the input stage output (29); a driver (40) for driving the light source and receiving electric power supply from the power buffer stage. The power input stage generates output current pulses for charging the power buffer stage at a relatively low frequency, and during each output current pulse, the power input stage draws input current, the input current always having a current magnitude higher than a minimum load requirement of the electronic transformer.

Abstract: A control device for regulating the constant output current of a flyback converter, the control device adapted to control the on time period and the off time period of a primary winding switch and including a first circuit adapted to multiply a first signal representative of current flowing through the primary winding and a second signal representative of an input voltage and outputting a signal representative of the multiplication, a second circuit adapted to compare the output signal of the first circuit and a third signal representative of the direct output voltage, the control device determining, on the basis of the output signal of the second circuit, the on time period and the off time period of the switch so that the output signal of the first circuit is equal to the signal representative of the direct output signal to have the output current of the flyback converter constant.

Abstract: A high-pressure discharge lamp ballast is provided for igniting and re-igniting a high-pressure discharge lamp in various states of operation. A power supply circuit is coupled to a power source and supplies AC power to the lamp. An ignition voltage generating circuit supplies a high-voltage ignition pulse for igniting the lamp. A pulse control circuit alternatively controls the ignition voltage generating circuit in a first control mode to provide the high-voltage ignition pulses for a first time period and in a second control mode to delay the high-voltage ignition pulses for a second time period. An abnormality detection circuit detects an abnormal lighting state of the lamp wherein a measured condition of the lamp corresponds to a predetermined condition. The pulse control circuit increases a ratio of the second time period relative to the first time period upon detection of an abnormal lighting state of the lamp by the abnormality detection circuit.

Abstract: The present invention relates to a circuit arrangement having a transformation apparatus, which has a primary side (P) and a secondary side (S), wherein the primary side and the secondary side (S) are DC-isolated from one another, wherein the primary side (P) has a terminal for a supply voltage (UE) and is connected to a first reference potential, wherein the secondary side (S) comprises a first and a second output line, which, in the normal case, are not coupled to a reference potential and which form an output terminal, at which a voltage for a load (LA) can be provided, wherein it furthermore comprises: an apparatus for tapping off a measured voltage potential (CP) on the secondary side (S); and an apparatus (10) for determining whether the measured voltage potential is in a permissible range. The invention moreover relates to an operating method for a lamp using a circuit arrangement.

Abstract: An LED current-balance driving circuit for driving a plurality of LED strings comprises a feedback transformer, a plurality of current-balance transformers, a plurality of full-wave rectifiers and a current control circuit. The feedback transformer has a detecting winding and an outputting winding for outputting a feedback signal. Each of the current-balance transformers has a primary winding and a secondary winding. The primary windings of the current-balance transformers and the detecting winding of the feedback transformer are coupled in series to compose a current-balance loop with an AC power being supplied thereto. Each of the full-wave rectifiers is coupled between a corresponding secondary winding of the current balance transformers and a corresponding LED string of the LED strings. The current control circuit receives the feedback signal and controls the AC power according to the feedback signal.

Abstract: A power supply system is provided for a multiple lamp LCD panel. In one aspect, the power supply includes a plurality of transformers for driving a plurality of respective CCFLs. The primary sides of each transformer are coupled in series to thereby reduce the stress on each transformer. For LCD panels that include longer CCFLs, a power supply is provided that includes a plurality of transformers for driving a plurality of respective CCFLs. The primary sides of each transformer are coupled in series and each lamp is coupled to two secondary sides of the transformers, thereby reducing the problems associated with longer CCFL tubes. In any of the embodiments, the power supply can be adapted to convert a high voltage DC signal to high voltage AC used to power the lamps.

Abstract: A light source apparatus and a light source adjusting module are provided. The light source apparatus includes a power supply, a phase modulator, an electrical transformer, a light source adjusting module and a light-emitting device. The power supply provides a first AC voltage signal. The phase modulator receives the first AC voltage signal and adjusts a conducting phase of the first AC voltage signal to generate a modulated AC voltage signal. The electrical transformer transforms the modulated AC voltage signal to generate a second AC voltage signal. The light adjusting module generates a luminance adjusting signal according to a state of the second AC voltage signal. The light-emitting device receives the luminance adjusting signal to generate a corresponding light source.

Abstract: To prevent the continuation of the abnormal state occurring immediately after the lighting start of the electrodeless discharge lamp excited by a DC driven magnetron and to recover promptly from the abnormal state at the steady state period. Lighting start of an electrodeless discharge lamp is performed in soft start mode. Increasing the power supply to the magnetron gradually, the lamp is turned into a lighting state for longer time than the time for the luminescence medium to evaporate fully absorbing microwave. At that period, the output of DC power supply is periodically cut off momentarily, resetting the abnormal state. Then, stable DC power is supplied. At the steady state period, the anode current of the magnetron is controlled to be constant. When rise of the operation voltage of the magnetron is detected, the output of DC power supply is cut off momentary to recover to the steady state.

Abstract: A lighting device implemented through utilizing an insulating type piezoelectric transformer in driving light-emitting-diodes (LEDs), comprising at least said insulating type piezoelectric transformer connected to an LED module, a primary side of said insulating type piezoelectric transformer is used to receive a pulse voltage, and that is converted into an AC voltage in a piezoelectric voltage transformation way, and said AC voltage is output from a secondary side of said insulating type piezoelectric transformer to said LED module in proceeding with lighting function. Due to its various advantages of small leakage current, good insulation capability, high voltage endurance, low operation temperature, compact size, thin profile, high energy conversion efficiency, said insulating type piezoelectric transformer can be used to not only raise lighting efficiency, but also reduce overall size of said lighting device.

Abstract: System and method for driving a cold-cathode fluorescent lamp. The system includes a control subsystem configured to generate one or more control signals, and a power supply subsystem configured to receive the one or more control signals and a DC input voltage, convert the DC input voltage to an AC output voltage, and send the AC output voltage to a cold-cathode fluorescent lamp. If the DC input voltage is lower than a predetermined threshold, the system for driving the cold-cathode fluorescent lamp is turned off in response to the one or more control signals.

Abstract: A LED driving circuit includes a transformer, a rectifying filtering circuit, a PWM IC, a constant current circuit, and a feedback circuit. The transformer has a primary side and a secondary side. The rectifying filtering circuit is coupled to the secondary side and has a first output terminal. The PWM IC is coupled to the primary side. The constant current circuit has a second output terminal. A LED load is adapted to couple between the first output terminal and the second output terminal. The feedback circuit has a first input terminal coupled to the first output terminal to receive a first voltage and a second input terminal coupled to the constant current circuit to receive a second voltage. The second voltage varies with a conduction status of the LED load. The feedback circuit is adapted to control the PWM IC according to the received first and second voltages.

Abstract: A light source driving device includes a power factor correction (PFC) circuit, a power stage circuit, a power conversion circuit, a balancing circuit, an inverter control signal processor, an inverter controller and an isolation component. Alternating current (AC) signals are converted into electrical signals to drive lamps via the PFC circuit, the power stage circuit, the power conversion circuit and the current balancing circuit. The power conversion circuit including a transformer divides the driving device into a primary side and a secondary side. The inverter control signal processor receives a first control signal output from a secondary side and generates a second control signal. The inverter controller is disposed on the secondary side to drive the power stage circuit. The isolation component transmits the second control signal to the inverter controller and isolates the inverter control signal processor from the inverter controller.

Abstract: A display apparatus and a power circuit device thereof are provided. The power circuit device includes: a transforming unit which outputs a first output current and a second output current in response to change of an input current; a first switching unit which switches to allow the input current to be selectively input; a first switch control unit which controls the first switching unit so that an operation voltage of the display apparatus reaches a first target value; a second switching unit which switches to allow the second output current to be selectively output; a backlight driving unit which drives the backlight based on the second output current; and a second switch control unit which controls the second switching unit so that a driving voltage of the backlight reaches a second target value.

Abstract: Disclosed is a method for controlling a series circuit current of a lighting installation at an airfield or the like, in which case the series circuit current which flows through transformers which are arranged on the secondary side of an output transformer and are connected in series, in order to supply lighting appliances is controlled by means of a thyristor module, which is arranged on the primary side of the output transformer and has a variable trigger angle, in which case, when a control unit is in a constant-current mode, the trigger angle is set in such a manner that a series circuit current which corresponds essentially to a rated output current flows. The invention also relates to a constant-current regulator for carrying out the method.

Abstract: A method is provided for driving at least one lamp unit, which is connected to an AC voltage power supply system. The method comprises modulating a control information item for the operation of the lamp unit onto the supplied AC voltage, decoding of the modulation received on the lamp unit side for reading the control information item and driving the light-emitting device in accordance with the control information item. Provision is made for a shunt to be produced in the line used for transmitting the control information item prior to or at the beginning of the modulation of the control information item. The disclosure also provides a lamp unit and a control device for implementing the method. The disclosure also provides a lighting system.

Abstract: A high pressure discharge lamp lighting device includes a DC power source circuit; a power supply circuit for converting an output from the DC power source circuit into a square wave AC output to be supplied to a high pressure discharge lamp; a starting circuit for applying a high voltage output for lamp startup to the high pressure discharge lamp; a control circuit; and a half-wave discharge detection circuit for detecting a half-wave discharge. The detection circuit detects the half-wave discharge at an initial stage of the lamp startup and the control circuit controls the magnitude of a voltage of a square wave half period of one polarity having a load voltage of a larger magnitude and that of a square wave half period of the other polarity having a load voltage of a smaller magnitude to approximate to each other.

Abstract: A method and firmware for controlling an inverter voltage includes steps of receiving as input a digitized feedback signal representative of an inverter voltage that varies with frequency according to a transfer function, calculating a frequency of a digital switch control signal in firmware in an inverter voltage microcontroller by the transfer function from the digitized feedback signal to adjust the inverter voltage to a set point value, and generating the digital switch control signal having the calculated frequency by firmware in the inverter voltage microcontroller as output to generate the inverter voltage at the set point value.

Abstract: A method and firmware for controlling voltage and current in an electrical load includes steps of calculating a numerically quantized duty cycle of a pulse-width modulated, digital switch control signal by firmware in an inverter voltage microcontroller as a function of an inverter voltage and controlling the inverter voltage by adjusting the duty cycle of the digital switch control signal to generate a load current in the electrical load.

Abstract: The present invention discloses a control apparatus, which not only accepts multiple dimming control signals, but also combines the signals in analog manner. By means of this, an inevitable analog to digital converter in a conventional voltage multiple dimming control apparatus can be saved without hurting the performance of generation of pulse width modulation signals. Compared with the conventional arts, the present invention further exhibits reduction in view of chip size and power consumption.

Abstract: A driving circuit of multi-lamps including a power supply module, a transformer module, a first detection module, and a control module is provided. Whether the power supply module is turned off is controlled by a control signal. The transformer module respectively provides a driving signal and an inverted driving signal to a first terminal and a second terminal of each lamp according to the AC signal. The first detection module detects a first indication signal combined by signals of the first terminal of one lamp and the second terminal of another lamp. The control module generates the control signal according to the first indication signal. Therefore, whether the lamps have a problem of a short circuit or an open circuit, or are in abnormal states can be known from the variations of the first indication signal, and a protection function for the driving circuit can be activated.

Abstract: In a backlight unit and an LCD apparatus having the backlight unit, in which the backlight unit includes a plurality of lamps and an inverter, the inverter provides the lamps with current. The inverter reduces current provided to the lamps to turn off the lamps. Therefore, currents are gradually decreased to reduce noise generated by the transformer when the lamps are turned off.

Abstract: A backlight driving system comprises an inverter module, a current balance module, a feedback module and an open-lamp protection detection module. The inverter module provides electrical signals to a plurality of lamps. The current balance module balances currents flowing through the plurality of lamps. The feedback module detects the current of the backlight and generates a feedback signal to the invert module accordingly. The open-lamp protection detection module detects voltage variations of the feedback transformer and generates a detection signal to the inverter module accordingly. The inverter module regulates the currents flowing through the plurality of lamps according to the feedback signal and determines one or more of the plurality of lamps are faulty according to the detection signal generated by the open-lamp protection detection module, and stops providing the electrical signals to the plurality of lamps.

Abstract: An illumination system includes a master power supply providing power to several illumination modules. The master power supply is constructed and arranged to generate high-frequency and low-voltage electrical power provided to a primary wire forming a current loop. Each illumination module includes an electromagnetic coupling element and several light sources. The electromagnetic coupling element includes a magnetic core arranged to receive the current loop in a removable arrangement, and a secondary wire wound around the magnetic core to enable inductive coupling. The secondary wire is connected to provide current to the light sources that may be arranged in the illumination module as a DC load or an AC load.

Abstract: A discharge lamp lighting device includes: a DC power source; an inverter for inverting the DC power at a predetermined inversion time interval to supply a square wave AC power to a discharge lamp; and a controller for controlling the output power. The controller performs a synchronous operation and controls the DC power source such that DC power outputted during a period other than the output temporarily increasing period in a power increasing period is greater than the DC output power outputted during the period other than the output temporarily increasing period in a rated power period. Further, the controller controls the DC power source such that at least one of an increment of the output power for the output temporarily increasing period and a length of the output temporarily increasing period is less in at least a part of the output increasing period than in the rated power period.

Abstract: The present disclosure thus provides a technique for providing multi-level operation of ballast circuitry for discharge lamps. In one version, an auxiliary capacitance is switched in and out of circuit by a user controlled switch for lower the frequency of the voltage from the inverter to the transformer resulting in lower power output to the lamps. In another version, the auxiliary capacitance may be switched in and out of circuit by a user operated switch wherein the capacitance is connected to the secondary or output winding of the transformer for selectively reducing power to the lamps for reduced illumination. In other versions, auxiliary inductances are selectively switched in and out of circuit to alter the frequency of the primary voltage to the transformer. In another version, an auxiliary winding is selectively switched in and out of the secondary of the transformer for providing normal and reduced level power to the lamps.

Abstract: A double-ended, DC-AC converter supplies AC power to a load, such as a cold cathode fluorescent lamp used to back-light a liquid crystal display. First and second converter stages generate respective first and second sinusoidal voltages having the same frequency and amplitude, but having a controlled phase difference therebetween. By employing a voltage controlled delay circuit to control the phase difference between the first and second sinusoidal voltages, the converter is able to vary the amplitude of the composite voltage differential produced across the opposite ends of the load. The converter may be either voltage fed or current fed.