Abstract: A power supply device includes a convertor and an arithmetic circuit. The convertor supplies electric power by performing an ON and OFF operation of a switching element. The arithmetic circuit calculates a control command value at predetermined intervals based on a digital value, which reflects an output voltage of the convertor, from a conversion circuit. Based on the control command value, a pulse signal generation circuit determines a duty ratio of a pulse signal to make the output voltage of the convertor stable. A driving signal with a finely adjusted duty ratio can be generated by an operation clock signal having a lower frequency than a conventional device. As a result, the number of output lines is appropriate if there is at least a single output line for the pulse signal from the pulse signal generation circuit.

Abstract: A power supply device includes a converter and an arithmetic circuit. The arithmetic circuit calculates a present control command value at predetermined intervals based on a digital value, which reflects an output voltage of a converter, from a conversion circuit. The arithmetic circuit calculates the difference value between the present control command value and a previous control command value. Based on the difference value, it is determined whether a signal output circuit outputs a high-level signal toward a charge terminal or a low-level signal toward a discharge terminal. As a result, the number of output lines corresponds to at least the number of charge terminals and discharge terminals. The above features can be achieved with a simple circuit configuration by adding a discharge and charge circuit and without increasing the number of output lines.

Abstract: Light flux levels sensed from a color LED array control both current availability to the array and disable/re-enable a current bypass switch to shunt stored-energy current to or away from a selected LED. In continuous mode, a single flux pulse is created for the duration of a pre-established period. Feedback from the flux sensor pulses current to an energy storage device to maintain the light flux at a predetermined set-point. A particular dimming level is achieved by establishing both the pulse period and the flux magnitude. In discontinuous mode, one or more short flux pulses are created. Both the turn-on and the turn-off time of each flux pulse is controlled by alternately removing and then re-establishing a current shunt from the energy storage device to ground. Flux pulse magnitude is controlled by recognizing when the flux pulse has reached a predetermined set-point and re-establishing the current shunt to abruptly turn off current to the selected LED.

Abstract: Embodiments of the present invention provide a system and method for controlling the amplitude of a current from a diode bridge into an EMI filter and LED array. Due to the manner in which certain dimmers (i.e., leading edge dimmers) operate, there is a delay on its output in transmitting a voltage when the voltage crosses zero.

Abstract: A lighting system converter circuit of a lamp power converter to selectively operate a plurality of lamps connected thereto is provided. The lighting system converter circuit includes a first impedance circuit and a second impedance circuit. Each impedance circuit includes an input terminal, an impedance component, and a switching network. The impedance components are each configured to connect in series with the lamps. Each input terminal is configured to receive a control signal that indicates a state of a switch. Each control signal has a first logic level, indicating the switch is non-conductive, and a second logic level, indicating the switch is conductive. Each switching network is connected to its respective input terminal and in parallel with its respective impedance component, and is configured to selectively operate between a conductive state and a non-conductive state, as a function of the logic level of its respective control signal.

Abstract: A method and apparatus for optimizing a light emitting diode (LED) operation range is provided. The method comprises the steps of: turning on at least one LED; and then measuring an anode voltage of the at least one LED; then measuring a cathode voltage of the at least one LED. Once the measurements are completed, a forward voltage of the at least one LED is calculated. After the calculation, the at least one LED is turned off and a power multiplier switch threshold is set for that LED based on the measured anode and cathode voltages.

Abstract: A driving circuit includes: a first voltage dividing circuit arranged to generate a first voltage-divided signal according to a supply voltage; a second voltage dividing circuit arranged to generate a second voltage-divided signal according to specific voltage; a coupling circuit coupled between the first voltage dividing circuit and the second voltage dividing circuit, and arranged to couple the first voltage-divided signal into the second voltage-divided signal to generate a coupling signal; and a control circuit arranged to generate a control signal at least according to the coupling signal and a feedback signal to control a duty cycle of a transistor, wherein the feedback is generated by the transistor.

Abstract: A system and method for operating one or more light emitting devices is disclosed. In one example, the switching of a regulator is ceased in response to a request to stop supplying power to one or more light emitting devices. The approach may reduce power consumption of a lighting system when light is not requested.

Abstract: An apparatus for driving a light source of a backlight unit includes: light sources; and a light source driver operating in an idle mode according to an input dimming signal and reducing a dimming value of an output dimming signal for adjusting brightness of the light sources by stages by mixing PWM control and PWM count control in a time-series manner to thus implement low dimming in the idle mode, wherein the dimming value of the output dimming signal is lowered to a first dimming value through the PWM control during a first period and subsequently lowered to a second dimming value lower than the first dimming value through the PWM count control during a second period that follows the first period.

Abstract: An apparatus may include a backlight for illuminating a liquid crystal display and a control module for controlling the illumination of the backlight. The control module may alternate between turning the backlight on and off at a first frequency and turning the backlight on and off at a second frequency.

Abstract: The display device includes a light source, and a control section adapted to generate a composite pulse width modulation signal using PWM1 having a first Duty ratio and PWM2 having a frequency higher than the frequency of PWM1, and control a light emitting state of the light source using the composite pulse width modulation signal. The control section corrects a second Duty ratio based on a difference between an expected value of luminance obtained when making the light source emit light using a virtual pulse width modulation signal, which is obtained by combining PWM1 and a pulse width modulation signal having the second Duty ratio, and a setting value of luminance based on the information related to the luminance of the light source, and then uses the second Duty ratio corrected as the Duty ratio of PWM2.

Abstract: An LED control circuit with auto ON/OFF function has a power module, a control module, a timer module, a driver module and an LED module with a first LED unit and a second LED unit. The control module generates a time control signal and an LED control signal to respectively activate the timer module and the LED module. The LED module is activated by the LED control signal only when the timer module is turned ON. The timer module can be automatically turned ON/OFF by the time control signal. Moreover, the LED control signal has high potentials and low potentials. The driver module activates the first LED unit and the second LED unit based on two the different potentials of the LED control signal respectively. Both high and low potentials of the LED control are used. The performance of the LED module is improved.

Abstract: In some embodiments, a light device for generating light includes light emitting diodes (LEDs), and power supply circuitry including at least one switching regulator including switching elements to provide power to the LEDs. The light device includes a device support structure including a device connector and an LED support to support the LEDs, wherein the device connector is one end of the device support structure, and the power supply circuitry is supported by the device support structure. Other embodiments are described.

Abstract: The present invention discloses a lighting lamp (10), is used for emitting a plurality of lights with different color temperatures, and color rendering indexes of all the lights are larger than 90. The lighting lamp (10) includes a combination (100) of light sources and a driving module (200). The combination (100) of the light sources includes four LEDs with specific wavelengths. The driving module (200) is utilized to drive the LEDs to illuminate and to control energy distribution of luminous energy for the first, second, third and fourth LEDs, thereby dynamically adjusting to show the light with 9000K, 12000K and eight color temperatures defined by the ENERGY STAR.

Abstract: The light emitting device control circuit device 100 in accordance with the disclosure includes a power source V1, a transistor TR1, a light emitting unit EU1, switches S1 to S17, constant current sources CC1 to CC17, and a controller 110. A switching voltage Vs1 is supplied from the controller 110 to turn ON or turn OFF the transistor TR intermittently, a pulse voltage is supplied to a pulse voltage supplying line Y1 connected to a drain terminal D of the transistor TR1. The driving signals SP1 to SP17 are sequentially supplied to the switches S1 to S17 to turn ON or turn OFF them (i.e., time division drive). The light emitting devices A1 to A17 are driven sequentially by a pulse current (i.e., time division drive) when a high voltage is supplied to the pulse voltage supplying line Y1 and when the driving signals SP1 to SP17 are turned ON.

Abstract: An LED driving apparatus for suppressing harmonic components is provided. First and fourth portions 21 and 24 are in parallel to the first and second LEDs 11 and 12, respectively. The first portion 21 controls the current amount in said first LED 11. The fourth portion 24 controls the current amount in said first and second LEDs 11 and 12. The first and fourth controllers 31 and 34 control the first and fourth portions 21, respectively. A current detector 4 detects a signal based on the amount of a current flowing from the first and second LEDs 11 and 12. A signal providing portion 6 provides a voltage based on a rectified voltage provided from a rectifying circuit 2. The first and fourth controllers 31 and 34 compare the current detection signal with the signal voltage, and control the first and fourth portions 21 and 24 based on the comparison.

Abstract: A capacitive touch sensor and LED driver device achieves a reduction in pin count by multiplexing LED drive functionality and capacitive sense functionality on each input/output pin. A control circuit switches between LED drive mode and capacitive sense mode at a frequency of approximately 200 Hz, although other switching frequencies can be used. A bias driver functions as a current sink for LEDs in LED drive mode and can also be used to drive a bias voltage to the LEDs during capacitive sense mode to improve noise immunity.

Abstract: A circuit with adjustable phase delay and a feedback voltage includes a delay setting unit and a phase delay signal generator. The delay setting unit generates a delay time according to an external resistor. The phase delay signal generator includes a plurality of phase delay units. Each phase delay unit includes an edge trigger subunit and a signal generation subunit. The edge trigger subunit receives an input signal, and generates a positive edge trigger signal and a negative edge trigger signal according to a positive edge and a negative edge of the input signal, respectively. The signal generation subunit generates and outputs a phase delay signal according to the positive edge trigger signal, the negative edge trigger signal, and the delay time. The phase delay signal lags the input signal for the delay time.

Abstract: Various embodiments of an LED dimming driver are disclosed herein. In some embodiments, an apparatus for dimmably driving at least one load includes a power supply having a voltage output, a controller having at least one current setpoint output, and at least one driver channel circuit connected to the voltage output of the power supply and to at least one of the at least one current setpoint outputs, the at least one driver channel circuit having a load output.

Abstract: The invention provides a thin film transistor having current driving force that can be substantially improved. By heat treatment, the IGZO layer (45) from which oxygen is taken away by the titanium electrodes (65) becomes the low resistance regions (40b), and the IGZO layer (45) from which oxygen is not taken away remains as the high resistance region (40a). In this state, when the gate voltage is applied to the gate electrode (20), electrons in the low resistance regions (40b) near the boundaries with the high resistance region (40a) move respectively to the titanium electrode (65) sides. As a result, the length of the low resistance regions (40b) becomes short, and oppositely, the length of the high resistance region (40a) becomes longer by the size of the shortened low resistance regions. However, the electrical channel length (Le) becomes shorter than the source/drain interval space (Lch) as the limit resolution of the exposure device, and the current driving force becomes large.

Abstract: A system is disclosed to automatically establish proper biasing for light sources in a color mixed projection system having multiple light sources which are active at the same time. Responsive to a feedback signal, a single DC-DC converter generates the bias voltage for the light sources. Comparators compare a headroom signal for each light source to a reference value to generate comparator output signals. The comparator output signals are processed by a channel selector and a digital filter/DAC module. The channel selector controls a switch to selectively provide and combine a headroom signal with an output of the digital filter/DAC module to create the feedback signal. By monitoring each headroom value, the bias voltage is adjusted, based on the feedback signal, until every headroom signal reaches the reference value thereby achieving sufficient biasing for every active light source in the color mixed projection system.

Abstract: A system and method include a controller that reduces power dissipated by a switch, such as a source-controlled field effect transistor, when an estimated amount of power dissipated by the switch exceeds a predetermined threshold. Reducing the power dissipated by the switch prevents damage to the switch due to overheating. The controller determines the estimated amount of power dissipated by the switch using actual drain-to-source current and drain voltage data. In at least one embodiment, the controller includes a fail-safe, estimated power dissipation determination path that activates when the drain voltage data fails a reliability test. Additionally, in at least one embodiment, the controller includes a model of thermal characteristics of the switch. In at least one embodiment, the controller utilizes real-time estimated power dissipation by the switch and the model to determine when the estimated power dissipated by the switch exceeds a power dissipation protection threshold.

Abstract: A marking device includes a solid-state light-emitting element as a light source. A plurality of the marking devices are arranged spaced apart from one another, wherein the solid-state light-emitting element is subjected to PWM control and lit at a frequency of 100 Hz to 200 Hz or exceeding 2,000 Hz.

Abstract: An electric lighting driver circuit for driving an illuminating unit to emit light includes a flyback converting unit for converting a DC input voltage to a low ripple DC voltage, and a half-bridge converting unit electrically connected to the flyback converting unit, for converting the low ripple DC voltage to a low frequency, rectangular wave output voltage to drive the illuminating unit to emit light. The flyback converting unit includes a dual-output winding transformer connected to the half-bridge converting unit. The dual-output winding transformer includes a first winding at a primary side of the dual-output winding transformer and a second winding and a third winding at a secondary side of the dual-output winding transformer. The third winding converts leakage inductance attributed to the first winding and the second winding to electrical energy that is provided to the half-bridge converting unit.

Abstract: A power supply apparatus includes a first constant-power power supply that switches and supplies powers of j types (where j is a natural number of two or more), a second constant-power power supply that switches and supplies powers of k types (where k is a natural number of two or more), and a switching controller that selects and switches on the first and second variable-power power supplies, excluding power transition periods thereof, to supply a load with a constant power.

Abstract: A driving device comprises a first transistor (B13), a second transistor (B14), and a resistance element. The first transistor (B13) has one terminal receiving a pulsed current and a control terminal connected to the one terminal. The second transistor (B14) has one terminal connected to at least one load, the other terminal connected to a reference potential together with the other terminal of the first transistor (B13), and a control terminal connected to the control terminal of the first transistor (B13). The resistance element is connected between the control terminal of the first transistor (B13) and the other terminal of the first transistor (B13).

Abstract: Technologies are described herein for an illumination device and a corresponding fixture device. The illumination device includes a luminary module for the emission of light and an identification circuit containing identifying data, while the fixture device includes a driver module for supplying power to the illumination device and a controller module. When the illumination device is connected to the fixture device, the controller module communicates with the identification circuit of the illumination device to retrieve the identifying data and causes the driver module to supply the appropriate power to the luminary module of the illumination device.

Abstract: A load control device, such as an electronic ballast, for controlling the power delivered from an AC power source to an electrical load, such as one or more fluorescent lamps, comprises a power converter having an inductor and a power switching device coupled to the inductor, a load control circuit adapted to be coupled to the electrical load, and a control circuit operable to calculate an average input power of the load control device. The control circuit may be operable to calculate a cumulative output power of the power converter while the ballast is preheating filaments of the lamps, and to subsequently determine a fault condition in the lamps in response to the calculated cumulative output power of the power converter. Further, the control circuit may be operable to transmit a digital message including the calculated average input power of the load control device.

Abstract: An LED lighting device includes: a resistor R1 configured to output a detection value of an inductor current I1 flowing through an inductor L1 during an ON period of a switching element Q1; a threshold generation section 42 configured to generate a threshold value Vs of the inductor current I1 corresponding to a dimming level; and a switching control section 44 configured to control the switching element Q1 to turn on and off. The switching control section 44 is configured to determine an OFF timing of the switching element Q1 based on comparison between the detection value and the threshold value Vs of the inductor current I1. The LED lighting device increases a period of a switching cycle of the switching element Q1 with decrease of the dimming level.

Abstract: A fixing device of a light-emitting body, whose mounting height is suppressed, is provided. Further, a lighting device whose mounting height is suppressed is provided. Further, a lighting device whose mounting height is suppressed and in which fixtures supporting a light-emitting body are hidden from view is provided. Furthermore, a lighting device whose mounting height is suppressed and in which light-emitting bodies can be arranged with no space therebetween and supported is provided. A structure is employed in which a planar light-emitting body whose thickness is suppressed is formed using an organic electroluminescent element, a terminal is provided in each of end portions facing each other in the planar light-emitting body, the terminals are made in contact with contacts provided in fixtures, and the end portions of the light-emitting body are held between the fixtures.

Abstract: A LED tube includes a translucent or fluorescent tube of substantially the shape and size of a fluorescence tube, inside which one or more LED components and a current control unit are installed. At both ends of the LED tube, there is a pair of contact pins for connecting the light element mechanically and electrically to the tube holders of the fluorescence tube lighting fixture. The tube lamp has a safety unit arranged to prevent a voltage from transferring through the tube lamp from its one end to the other until a voltage supplied from the corresponding tube holder of the lighting fixture to the pair of contact pins has been separately detected at each end of the tube lamp. Inside the LED tube, there is at least one optical line that is arranged to transfer a control or measurement signal associated with the safety unit from one end of the LED tube to the other without capacitive leakage currents.

Abstract: There is provided a light emitting diode driving apparatus for controlling the light emitting diode driving according to a feedback signal input through a positive feedback loop, the light emitting diode driving apparatus including: a power converting unit switching input power and supplying driving power to at least one light emitting diode; a feedback unit detecting and feeding back a voltage of the driving power of the power converting unit; and a controlling unit including a comparator having a negative terminal receiving a reference voltage having a set voltage level and a positive terminal receiving the detected voltage from the feedback unit and comparing the reference voltage with the detected voltage to control a switching of the power converting unit according to a comparison result.

Abstract: A LED driver using a PWM signal for dimming control includes a power converter and a current regulator. The power converter provides an output voltage and a load current for a plurality of LEDs. The current regulator provides a load current dependent signal for the power converter to speed up load transient response caused by variation of the load current, to reduce the ripple of the output voltage, and thereby to avoid audio noise during PWM dimming.

Abstract: A switched mode power converter is disclosed, together with a method for operating the same. The power converter is adapted to be operable in the boundary conduction mode, and operation is interruptible in the absence of any load requirement.

Abstract: A LED tube includes a substantially fluorescent-tube-shaped and fluorescent-tube-sized translucent or fluorescent tube having one or more LED components and a current control unit installed therein. Both ends of the LED tube are provided with a pair of contact pins for connecting the LED tube mechanically and electrically to the tube holders of the fluorescent tube lighting fixture. The tube has a safety unit arranged to prevent a voltage from transferring through the tube from its one end to the other until a voltage supplied from the corresponding tube holder of the lighting fixture to the pair of contact pins has been detected at each end of the tube separately. Electric power or switching control of electric power is cross-connected between the ends of the LED tube.

Abstract: A pixel driving circuit includes a first switch, a capacitor, a second switch and at least one organic light emitting diode. The first switch includes a first end for receiving data voltage, a control end for receiving a first scan signal, and a second end for outputting the data voltage. The capacitor includes a first end coupled to the second end of the first switch, and a second end. The second switch includes a first end coupled to the second end of the first switch, a control end for receiving a second scan signal, and a second end. The at least one organic light emitting diode includes a first end coupled to the second end of the second switch, and a second end coupled to the second end of the capacitor.

Abstract: A delayed light switch system and method is described herein. Such delayed light switch system can comprise a microphone in a first zone, a light switch, and a central computing system that connects to said microphone and said light switch, wherein said central computing system receives an audio signal from said microphone, said audio signal related to a sound detected by said microphone, waits for a delay time to pass, and transmits a first control signal to said light switch to turn said light switch on.

Abstract: A light-emitting element driving circuit system is provided in which a plurality of current paths, in each of which a light-emitting element and a switching element which is controlled to be switched ON and OFF for causing light to be emitted from the light-emitting element are connected in series, are placed in parallel to each other, wherein an ON time of each switching element is adjusted based on a light-emission period which is a period in which the light-emitting elements are caused to emit light in a circulating manner, such that a number of switching operations of each switching element is reduced.

Abstract: The invention relates to a lighting apparatus (1) having a lighting means (2) comprising at least one LED and having a first device (3) co-operating with a pulse width modulation device (4) for optionally adjusting a brightness of the LED. In order to simplify the maintenance of the lighting apparatus (1), it is proposed according to the invention that a memory (7) for storing at least one piece of information relating to the lighting means (2) and a second device (6) for generating a signal which encodes the information using the pulse width modulation device (4) are provided so that the signal can be transmitted by means of the LED as a pulse width-modulated light signal (L).

Abstract: A drive circuit is provided for supplying a drive current to drive a plurality of driven elements. The drive circuit includes a switch circuit having an input terminal for receiving a drive signal alternately changing between an on state and an off state, and an output terminal connected to the driven elements; and a constant current circuit connected to the switch circuit for adjusting the drive current at a constant level. The constant current circuit is formed of a depletion type MOS transistor.

Abstract: System and method for dimming control. The system includes a system controller, a transistor, and a resistor. The system controller includes a first controller terminal and a second controller terminal. The transistor includes a first transistor terminal, a second transistor terminal and a third transistor terminal. The resistor including a first resistor terminal and a second resistor terminal. The first transistor terminal is coupled, directly or indirectly, to the second controller terminal. The first resistor terminal is coupled to the second transistor terminal. The second resistor terminal is coupled to the third transistor terminal. The system controller is configured to receive an input signal at the first controller terminal and to generate an output signal at the second controller terminal. The transistor is configured to receive the output signal at the first transistor terminal and to change between a first condition and a second condition.

Abstract: An apparatus includes at least one LED, at least one charge storage device and a switching circuit configured to route current through the least one LED to the at least one charge storage device for a first state of an applied voltage and to discharge the at least one charge storage device via the at least one LED for a second state of the applied voltage. The apparatus may further include a current control circuit coupled in series with the at least one LED.

Abstract: The control method comprises the following steps. Firstly, whether a touch event occurs in a control device is determined. Then, responding to a color temperature set and a brightness set from the control device, a first PWM and a second PWM is generated. Then, whether the lamp connects with to the control device is determined. Then, the first PWM and the second PWM is packaged in a color control package if the lamp connects with to the control device. Then, the color control package is transmitted to the lamp in wireless.

Abstract: System and method for igniting one or more high-intensity-discharge lamps. A system includes an ignition controller configured to generate one or more signal pulses for a pulse signal during a first predetermined time period and to cause one or more voltage pulses to be applied to the one or more high-intensity-discharge lamps, the pulse signal changing between a first logic level and a second logic level during the first predetermined time period, each of the one or more signal pulses corresponding to a pulse period, the pulse period being no larger than the first predetermined time period. The ignition controller is further configured to, if the one or more high-intensity-discharge lamps are not successfully ignited after the first predetermined time period, stop generating any signal pulse for the pulse signal for a second predetermined time period, the second predetermined time period being equal to or larger than the pulse period.

Abstract: A lighting system provides for independent control of both the brightness of an LED light fixture and the perceived color of the light emitted by the LED light fixture. The LED light fixture has two LED light sources, a control circuit alternately pulses the two LED light sources and changes relative duty cycles of the light sources to alter a perceived color output of the lighting fixture, in response to a change in a control signal from a controller. Duty cycles of the light sources are a function of the control signal and vary inversely. The LED light fixture also receives a control signal for controlling a current level provided to the LED light sources to independently control the brightness of the lighting system.

Abstract: A circuit for operating at least one LED (“driver circuit”) includes input terminals to be connected to an input or operating voltage in the form of a direct current (DC) voltage or a rectified alternating current (AC) voltage, and output terminals to be connected to a load circuit containing the at least one LED. The circuit includes a clocked switch and a control circuit for clocking the switch. The control circuit is in the form of an integrated circuit (IC) and is provided with input and output pins. The control circuit generates a clock signal for the switch depending on at least two actual value signals, such that there is a control loop with the manipulated variable “clocking of the switch.

Abstract: A light emitting diode (LED) driver apparatus includes a pulse-width modulation (PWM) signal generator configured to generate a PWM signal according to a reference voltage. The LED driver apparatus also includes a DC-DC converter configured to provide a driving voltage to LED arrays based on the generated PWM signal, and a LED driver configured to drive the LED arrays through output ports. The LED apparatus includes a detector configured to detect whether the LED arrays are operatively connected to the corresponding output ports.

Abstract: An LED lighting device includes a plurality of kinds of LEDs 1 and 2 having different color temperatures, an LED lighting circuit 3 configured to light each of the plurality of kinds of LEDs, and a control unit 4 configured to control an LED lighting circuit to simultaneously dimmably light the plurality of kinds of LEDs, subject the plurality of kinds of LEDs to dimming control through pulse width control in a deep dimming region where a dimming degree is equal to or lower than 20%, and subject the plurality of kinds of LEDs to the dimming control through amplitude control in other dimming regions.

Abstract: A lamp control circuit includes a first switch circuit receiving a voltage from a power supply after a control is turned on and outputs a first control signal, a count circuit receives the first control signal and outputs a second control signal, a gate circuit receives the second control signal and outputs a third control signal, a second switch circuit includes a number of electronic switches to receive the third control signal and controls the electronic switches to be turned on or turned off, and a lighting circuit including a number of light emitting diode (LED) groups. Each LED group includes an LED. When an electronic switch connected to an LED group is turned on, the LED of the corresponding LED group is lit. When an electronic switch connected to an LED group is turned off, the LED of the LED group does not light.

Abstract: A control IC controls a switching power supply configured to supply a driving voltage Vout to one terminal of an LED string which is driven in an intermittent manner. A sample-and-hold circuit performs sampling of a detection voltage Vs that corresponds to a driving voltage Vout in the on period, and holds the sampled detection voltage Vs in the off period. In the off period, a pulse modulator generates a pulse signal having a duty ratio adjusted such that a hold detection voltage VsH output from the sample-and-hold circuit matches the detection voltage Vs. A driver drives a switching transistor according to the pulse signal.