Abstract: The present invention provides for a high voltage direct current power supply including a primary high voltage direct current supply offering a primary output; a floating secondary output floating with respect to the primary output and fed by the primary output: an output terminal at the floating secondary output for providing an output voltage; a controller operative to detect a change in the output voltage at the output terminal and to generate a control signal responsive to the change in output voltage; and a controllable current source, which can comprise a programmable current source, arranged to provide current at the floating secondary output responsive to the said control signal and whereby the said current is provided to reduce charging of a secondary output capacitance as the output voltage changes.

Abstract: A detector for a chromatograph includes a light source, and a light detector that detects light generated based on turning on of the light source, wherein the light source includes a deuterium lamp, and a deuterium lamp power supply circuit connected to the deuterium lamp, and the deuterium lamp power supply circuit includes a DC voltage generation circuit that generates a DC voltage by performing a switching operation, a rectifying operation and a smoothing operation, a voltage application circuit that applies a DC voltage generated by the DC voltage generation circuit to the deuterium lamp, a first feedback circuit that feeds a first feedback voltage changing depending on a DC voltage to the DC voltage generation circuit such that the DC voltage generated by the DC voltage generation circuit becomes close to a discharge maintaining voltage, after electric discharge of the deuterium lamp is started, and a constant current control circuit that controls a discharge current of the deuterium lamp to be constant.

Abstract: A method for regulating a temperature of a magnetron includes: determining an anode current flowing through the magnetron and an output power of a variable-frequency power supply, the output power being configured to drive the magnetron to operate; calculating an anode voltage of the magnetron according to the anode current of the magnetron and the output power of the variable-frequency power supply; calculating an anode temperature of the magnetron according to the anode voltage of the magnetron; and regulating the output power of the variable-frequency power supply according to the anode temperature of the magnetron.

Abstract: Provided is a method for monitoring DC electrical power. The method including determining a rate of change of the DC electrical power, determining whether the rate of change of the DC electrical power is greater than a predetermined threshold, when the rate of change of the DC electrical power is greater than the predetermined threshold, determining whether the rate of change of the DC electrical power is greater than the predetermined threshold for a predetermined period of time, and when the rate of change of the DC electrical power is greater than the predetermined threshold for the predetermined period of time, sending a signal indicating an interruption in the DC electrical power.

Abstract: In accordance with various embodiments, a coating arrangement may comprise: an electron beam gun for providing an electron beam; a beam trap for trapping the electron beam; a control device for driving the electron beam gun and/or the beam trap, wherein the control device is configured to switch over the driving between a plurality of configurations, of which: in a first configuration, the electron beam is directed onto the beam trap; and in a second configuration, the electron beam is directed past the beam trap.

Abstract: An x-ray system for simultaneously or concurrently measuring currents of multiple emitters is provided. The x-ray system includes a high voltage direct current (DC) supply configured to supply tube current to the multiple emitters and plural emitter circuits. Each of these circuits includes each comprising an alternating current (AC) voltage supply, at least one of the multiple emitters operatively coupled to the AC voltage supply and the high voltage DC supply, and a circuit coupling the AC voltage supply and the high voltage DC voltage supply to the at least one of the multiple filaments. At least one of the emitter circuits has a current measurement device between the high voltage DC supply and the emitter.

Abstract: Disclosed is a system for interacting with one or more containers placed near a conducting surface. The system sends the information of content inside the container in relation to an action caused by a user over the communication network. The system includes a controller; a frequency generator; a first electrode; an electronic circuitry including a convertor, an e-filed strength meter, an I/O interface and a bi-directional communication unit; a second electrode and a media unit. The controller generates a unique identification code for each container. The controller communicates through the communication network. The frequency generator provides a modulated alternating electric with variable frequency. The first electrode floats in the air inside the container and mirrors charges received from the frequency generator through the conducting surface and the content. The convertor converts alternating charges into DC energy received from the first electrode.

Abstract: An OBI manager provides the reduction/elimination of optical beat interference (OBI). As will be described in more detail below, the OBI manager identifies OBI partners through an identification process performed via an RFoG network. An OBI partner may be two optical networking units (ONUs) that may interfere with one another when transmitting in the same time slot. Once the OBI partners are identified, the OBI manager may perform a mitigation process to mitigate possible OBI. For example, the OBI manager may organize the OBI partners to reduce OBI, such as by guaranteeing no OBI partners transmit at the same time.

Abstract: An OBI manager provides the reduction/elimination of optical beat interference (OBI). As will be described in more detail below, the OBI manager identifies OBI partners through an identification process performed via an RFoG network. An OBI partner may be two optical networking units (ONUs) that may interfere with one another when transmitting in the same time slot. Once the OBI partners are identified, the OBI manager may perform a mitigation process to mitigate possible OBI. For example, the OBI manager may organize the OBI partners to reduce OBI, such as by guaranteeing no OBI partners transmit at the same time.

Abstract: An audio receiving system includes logic configured to reduce the accumulation of delays caused by the late arrival of audio packets. This logic is configured to accelerate or decelerate presentation of a resulting audio stream in response to the detection of late packets. The acceleration is discontinued once the effects of the late packets have been compensated for. The audio receiving system is typically applied to applications in which lag is undesirable. These can include web conferencing, telepresence, and online video games.

Abstract: A camera device. A housing includes a first portion, a second portion and a curved portion disposed between the first portion and the second portion and including a curved surface. The lens is disposed on an end surface of the housing. The image sensor is coupled to the lens for obtaining image data captured by the lens. The first input unit is disposed on the curved surface and provided as a first input interface for a user. The grip sensor is disposed on the first portion for sensing whether the first portion is held by the user. The lens and the image sensor operate in a sleep mode by default to reduce power consumption. When the grip sensor senses that the first portion is held by the user, the grip sensor generates a sensing signal to wake up the lens and the image sensor.

Abstract: A circuit to power an electron source includes a filament transformer comprising a primary side and a secondary side, a high-voltage transformer coupled to the filament transformer and the electron source, and an alternating current (AC) current limiter coupled in series with the primary side or the secondary side of the filament transformer. The AC current limiter includes a diode bridge and a current-limiting device in the diode bridge.

Abstract: An electronic dimming ballast for driving a gas discharge lamp may be operable to control the duty cycle of an independent filament drive (IFD) to avoid hard switching and operation of the switches of the IFD outside their safe operating area. Such a ballast may include a first inverter for generating a first high-frequency alternating current (AC) voltage for powering the gas discharge lamp, and a second inverter for generating a second high-frequency AC voltage for heating the filament, wherein the second inverter is driven independent of the first inverter. The second inverter may be configured to adjust a duty cycle of the second high-frequency AC voltage from a starting duty cycle to a target duty cycle at a rate. The rate may be controlled to be below a threshold. The ballast may include a controller for maintaining the rate below the threshold.

Abstract: A lighting ballast includes a filament drive reduction circuit with a first inductor coupled across a filament drive source, and a second inductor and a capacitor coupled in parallel to define an LC tank between a first end of the first inductor and the filament drive source. The inductance value of the second inductor and the capacitance value of the capacitor are selected such that the natural resonance of the LC tank is substantially equal to the normal operating frequency of the filament drive source, wherein the LC tank acts as an open circuit during normal operation and the first inductor acts to balance the pin currents of series connected lamp filaments. The first and second inductors are further substantially equal in value, wherein excess filament drive current is shunted away in accordance with a normal operating frequency.

Abstract: This disclosure provides a device for heating a cathode of a magnetron, which includes a heater for heating the cathode of the magnetron, a heater current detecting module for detecting a value of heater current that flows into the heater, and a control module for determining the completion of preheating of the magnetron based on a change in the heater current.

Abstract: A program-start ballast (100) that is connectable to a lamp (150) with a filament (151) is disclosed. The ballast includes a heating unit (170) arranged to heat the filament (151), a receiver (180) arranged to receive a signal to turn the lamp (150) on or off, and a control circuit (160) arranged to turn the lamp (150) on or off based upon an output of the receiver (180). The heating unit (160) is further arranged to heat the filament (151) before the signal to turn the lamp on is received by the receiver (180) and keep the filament (151) heated after the signal to turn off the lamp is received by the receiver (180).

Abstract: An electronic ballast for an electrical lamp (2) provided with a first (21) and a second filament (22), includes a heating device which is used to heat the filaments (21, 22) and includes a resonance circuit (5), and an evaluation unit (11) designed for the evaluation of at least one measuring value of an electrical parameter during pre-determinable adjustments of operating conditions of the resonance circuit (5). The number of filaments (21, 22) of the electrical lamp (2) in electrical contact with the electronic ballast (1) can be identified according to the measuring value, and the electrical lamp (2) can be switched on by the electronic ballast (1) according to the identified number. A method for operating an electrical lamp by an electronic ballast is also described.

Abstract: A circuit arrangement for operating a low-pressure discharge lamp may include a voltage source with two terminals; switches; and a series resonant circuit; a controller configured to control the switches such that an AC voltage is applied to the resonant circuit; a PTC thermistor coupled on one side to a circuit point of the resonant circuit and on the other side, at least one of via a diode, to the first terminal of the voltage source and, via a diode to the second terminal of the voltage source; a resistive element connected in series with a diode in the circuit between a terminal of the voltage source and the PTC thermistor; and an evaluation device configured to tap off the voltage drop across the resistive element and being coupled to the controller in order to deactivate the controller.

Abstract: An LED current control circuit including a current adjusting unit, a detecting unit, and a current control unit is provided. The current adjusting unit has a current control end coupled to an LED string for determining an amount of current flowing through the LED string according to a current control signal. The detecting unit detects the current control end and determines whether to generate a protecting signal according to a protecting voltage value. The current control unit generates the current control signal to control the amount of current flowing through the LED string of and determines whether to stop the current flowing through the LED string according to the protecting signal.

Abstract: A ballast circuit includes a filament cutback circuit to reduce a pre-heat voltage after the lamp filaments have been pre-heated. The filament cutback circuit includes a filament cut-back inductive component magnetically coupled to the resonant inductive component in the inverter to receive a filament cutback control voltage associated with an AC voltage for powering the lamps. During the pre-heating period, the filament cutback control voltage is not high enough to charge a chargeable component to a switch threshold level. However, during lamp ignition, the filament cutback control voltage is increased and charges the chargeable component to the switch threshold level. This causes a switch device to operate in a conductive switch state and the filament cutback circuit suppresses the pre-heat voltage.

Abstract: Method and apparatus for assuring use of a fluorescent or similar high efficiency lamp in a screw base socket, the invention provides a circuit containing a screw base socket and an associated thermal sensing unit capable of interrupting power to the circuit on sensing of heat such as is generated by an incandescent or similar low efficiency lamp when mounted in the screw base socket. Practice of the method permits use of only fluorescent or similar lamping such as is incapable of sufficient heat generation to interrupt power to the circuit, the methodology of the invention preventing use of incandescent or similar energy inefficient lamping. The method and apparatus are particularly useful in the lamping of recessed downlighting fixtures.

Abstract: A fluorescent-lamp-driving device contains a driving control circuit that receives direct current power voltage and a lamp control signal for performing drive control on fluorescent lamps and converts the direct current power voltage to alternating current power voltage, and a transformer containing a winding at its primary side and windings for driving a heater and for maintaining discharge at its secondary side. The alternating current power voltage is supplied to heaters of the fluorescent lamps at their high electric potential side. The driving control circuit increases the frequency of the alternating current power supply to a frequency thereof in which voltage of the fluorescent lamps is equal to a discharge start voltage of the fluorescent lamps or less based on the lamp control signal at a period of starting-up time of the fluorescent lamps.

Abstract: An electron source has an electron emitter with an electron emission cathode, a high voltage unit provided for power supply of the electron emission cathode, and a low voltage unit provided to control the high voltage unit. Data are transmitted non-electrically (in particular optically) between the high voltage unit and the low voltage unit.

Abstract: The method according to the present invention relates to controlling a gas discharge lamp during a pre-heating period of said lamp, wherein a first terminal of a control circuit is connected with a first electrode of the lamp and a second terminal of a control circuit is connected with a second electrode of the lamp, and wherein means are provided, suitable for connecting the first terminal and the second terminal with each other, thus providing a conducting path, and suitable for disconnecting the first terminal and the second terminal. Furthermore the method comprises the use of a chargeable and dischargeable power buffer, for powering control circuitry for operating the switching means.

Abstract: An arrangement for the regulation of the electron beam power of an electron gun, which comprises a filament cathode, a block cathode and an anode. Between the filament cathode and the block cathode is applied a first voltage, while between the block cathode and the anode a second voltage is applied. With the aid of a first closed-loop regulated system the filament cathode is regulated to a constant current value, which has a filament temperature sufficient for the maximum beam power of the block cathode. A second closed-loop regulated system, such including a block power regulator, which is acted upon by the difference between instantaneous block power value and nominal block power value, regulates the voltage between the filament cathode and the block cathode.

Abstract: At the time of restoration of the power supply after a power failure, a voltage higher than that in the normal operation mode is supplied to a heater. After a lapse of a predetermined time, the voltage to be supplied to the heater is switched into the voltage in the normal operation mode while a control signal for stating the operation of an electron tube is output. Alternatively, at the time of power activation, the rate of change of current flowing through a heater is determined for every period of time. When the rate of change becomes equal to or lower than a predetermined threshold, a voltage higher than that in the normal operation mode is supplied to the heater, and after a lapse of a predetermined time, the voltage to be supplied to the heater is switched into the voltage in the normal operation mode while a control signal for stating the operation of the electron tube is output.

Abstract: A light emission device and a display device having the light emission device are provided. The light emission device includes first and second substrates that are arranged to face each other, an electron emission unit that is located on a first surface of the first substrate facing the second substrate and has electron emission regions and driving electrodes, a light emission unit that is located on a surface of the second substrate and has an anode electrode and one or more phosphor layers, and a surface heat generation unit that is located on a second surface (or outer surface) of the first substrate facing away from the second substrate to control a temperature of the first substrate using a resistive layer having a positive temperature coefficient (PTC) property.

Abstract: The output current of a ballast is dynamically limited when an over-temperature condition is detected in the ballast according to one of (i) a step function or (ii) a combination of step and continuous functions, so as to reduce the temperature of the ballast while continuing to operate it.

Abstract: A lamp driving device includes a switch circuit for supplying a signal; a transformer which boosts a voltage of the signal from the switch circuit and supplies the boosted voltage to at least one lamp; a safety circuit which compares a threshold value with at least one of the boosted voltage and a current through the lamp, and intercepts at least one of the boosted voltage and the current through the lamp in accordance with the comparison result; and a warming part for warming the lamp in an early stage with a voltage less than or equal to the threshold value.

Abstract: A lighting ballast (10) includes an inverter portion (12) and a resonant portion (14). During a preheat phase, a filament transformer (110) supplies preheat glow currents to lamp cathodes. Also during the preheat phase, the filament transformer boosts the oscillation frequency of the inverter portion (12) to a frequency above a resonant frequency of the resonant portion (14). Once the lamp cathodes are sufficiently heated, the filament transformer (110) is removed from the circuit and the inverter (12) is allowed to start oscillating. A feedback network (150) monitors a high frequency bus (26) and provides input to a shunt regulator (170). The shunt regulator drives the gate of a switch (128) of a bias network (126) and adds or removes the filament transformer (110) to the circuit depending on the conductive state of the switch (128).

Abstract: A method for operating a charged particle beam emitting device and, in particular, an electron beam emitting device including a cold field emitter is provided. The method includes the steps of placing the cold field emitter in a vacuum of a given pressure, the emitter exhibiting a high initial emission current I0 and a lower stable mean emission current IS under a given electric extraction field; applying the given electric extraction field to the emitter for emitting electrons from the emitter surface; performing a cleaning process by applying at least one heating pulse to the cold field emitter for heating the emitter surface, whereby the cleaning process is performed before the emission current of the cold field emitter has declined to the lower stable mean emission value IS; and repeating the cleaning process to keep the emission current of the emitter continuously above the substantially stable emission value IS.

Abstract: The electronic ballast with lamp type determination for an electronic ballast providing power to a lamp filament 208 includes a filament current sensing circuit 220 operably connected to the lamp filament 208 and generating a sensed filament current signal, and a microprocessor U2 receiving the sensed filament current signal and operably connected to control the power to the lamp filament 208. The microprocessor U2 is programmed to heat the lamp filament by applying the power at a first frequency, measure the filament characteristics, and determine lamp type from the measured filament characteristics. The microprocessor U2 can also be programmed to update operating parameters for the electronic ballast to suit the determined lamp type.

Abstract: A system and method for developing a solid state stripper device is described that more effectively strips off negative carbon ions to produce positively charged carbon ions. In one embodiment the solid state stripping device is a self-supporting aggregate of nanotubes or Buckminster-Fullerenes. Such devices provide, among other things, carbon stripper foil for use in a tandem generator.

Abstract: The present invention applies to provide a lighting method of a high pressure discharge lamp dedicated particularly for image equipments in which re-lighting when turning ON the switch again immediately after the switch OFF is instantaneously performed even in the high pressure discharge lamp. In the transition state of transitioning from the lighted state to light off, the lamp power to be supplied to the electrodes (3), (4) is reduced to an extent an arc discharge does not disappear and maintained for a while, and thereafter, transitioned to the glow discharge after lowering the lamp temperature to a temperature capable of maintaining the glow discharge and maintaining the glow discharge for a while, and the current supply to the electrodes (3), (4) is cut at the point the lamp temperature becomes lower than or equal to the temperature at which re-lighting is possible.

Abstract: The present invention provides a method and circuit for accurately controlling heating of an electrode of a discharge lamp. According to the present invention a feedback voltage is generated. The feedback voltage is representative of an electrode voltage, in particular an electrode voltage when the discharge lamp is in a non-burning state, the electrode voltage then representing a heating voltage. The feedback voltage is compared to a predetermined reference voltage, which represents a desired heating voltage. The comparator generates and outputs an error signal representing a difference between the actual feedback voltage and the reference voltage. The error signal is supplied to a power supply circuit. The power supply circuit generates the alternating supply current corresponding to the error signal such that the electrode voltage is adjusted towards the desired heating voltage.

Abstract: A ballast (10) for powering at least one gas discharge lamp (70) having heatable filaments (72,74) includes an inverter (200), a resonant output circuit (400) coupled between inverter (200) and lamp (70), and a filament heating and ignition control circuit (600) coupled to inverter (200) and resonant output circuit (400) having a first resonant frequency and a second resonant frequency, wherein the first resonant frequency is substantially greater than the second resonant frequency. Filament heating and ignition control circuit (600) controls inverter (200) and resonant output circuit (400) during a preheat phase and during a normal operating phase. During the preheat phase, resonant output circuit (400) has an effective resonant capacitance corresponding to the first resonant frequency, and provides a first level of heating to the lamp filaments (72,74).

Abstract: A device which employs an electron beam, for performing a desired function, includes an electron gun for generating the electron beam. The electron gun includes a barrel shaped rotatable structure having a plurality of annularly disposed electron sources. A curvature of a surface portion of the rotatable structure is shaped to optimize electric field concentrations. The rotatable structure further includes end portion protrusions.

Abstract: A resonant igniter circuit (11) employs a switch ignition branch and a resonant ignition branch. The switch ignition branch includes a pair of ignition switches (M1, M2) connected in series with a switch node (N1). The resonant ignition branch includes an ignition coil (L2) and an ignition transformer (T2). Ignition coil (L2) is connected in series with switch node (N1) and a primary winding of ignition transformer (T2). In operation, a serial inductance of ignition coil (L2) is at least fifty (50) times greater than a resonant inductance of ignition transformer (T2) and ignition transformer (T2) has an air-gapped core between a primary winding and a secondary winding to thereby facilitate an impedance of a power stage of the resonant ignition branch as seen from a source as always being inductive over an entire range of output capacitance.

Abstract: At the time of restoration of the power supply after a power failure, a voltage higher than that in the normal operation mode is supplied to a heater. After a lapse of a predetermined time, the voltage to be supplied to the heater is switched into the voltage in the normal operation mode while a control signal for stating the operation of an electron tube is output. Alternatively, at the time of power activation, the rate of change of current flowing through a heater is determined for every period of time. When the rate of change becomes equal to or lower than a predetermined threshold, a voltage higher than that in the normal operation mode is supplied to the heater, and after a lapse of a predetermined time, the voltage to be supplied to the heater is switched into the voltage in the normal operation mode while a control signal for stating the operation of the electron tube is output.

Abstract: When a discharge lamp is preheated, impedance of a filament electrode of the discharge lamp is computed. In accordance with the computed impedance, preheating and lighting of the discharge lamp are controlled.

Abstract: A method of operating an arc discharge lamp that has first and second electrodes is described. First, the first electrode is heated with a third electrode with a first arc until the first electrode temperature is sufficiently elevated to allow for thermionic emission. Then, a first voltage is applied between the first and second electrode at a voltage less than 1000 volts to create a second arc.

Abstract: A ballast lamp circuit and method of operation is disclosed. The ballast lamp circuit comprising an inverter circuit and cathode heating circuit, wherein a lamp current, generated by the inverter circuit, is inversely proportional to a lamp cathode voltage generated by the cathode heating circuit.

Abstract: An electronic ballast capable of extending life of the fluorescent lamp is disclosed. The electronic ballast according to the present invention comprises a DC/AC converter, a fluorescent lamp, a transformer, a preheating transformer and an AC switch. Wherein, the AC switch is turned off during a preheating period of time for the fluorescent lamp. Due to adoption of a preheating transformer in the secondary side and an AC switch for the electronic ballast according to the present invention, the voltage drop across the fluorescent lamp can be reduced during the preheating period of time, and accordingly no glow current would appear. Therefore, life of the electronic ballast can be effectively extended.

Abstract: In a current fed electronic ballast multiple lamps are operated in a parallel circuit arrangement. The ballast provides pre-heating to the cathodes of the lamps for a period of time before an open circuit voltage is ramped up to the preferred starting voltage of the lamps. An open circuit voltage controller times coordinates the pre-heating and the operating voltage. After the pre-heating phase, current is removed from the cathodes of the lamps so that electricity is not wasted to the cathodes while the lamps are lit. A single switch is used to switch cathode pre-heating on and off, regardless of how many lamps the ballast operates. A decoupling array of diodes allows the single switch to coordinate pre-heating to all the lamps.

Abstract: In an operating method for a lighting system and a lighting system in which a readiness command is provided, in response to such readiness command a ballast drives a discharge lamp in such a way that it heats the electrodes further if the discharge lamp is not burning, so that a controller can use a switch-on command to reignite the discharge lamp without delay by means of a preheating time.

Abstract: A microwave excited ultraviolet lamp system having a single electrical cable that supplies operating voltages from a power supply to a lamp head. The single electrical cable may provide high voltage to a magnetron of the lamp head and a lesser voltage to an internal blower of the lamp head. The electrical cable may incorporate conductors for transferring communications signals between the power supply and sensors associated with the lamp head.

Abstract: In accordance with one aspect of the present application, a lamp inverter circuit includes a switching portion that converts a bus voltage signal into an alternating current signal. An input portion receives the bus voltage signal, and a resonant load portion drives a lamp. A preheating portion heats the lamp prior to ignition, and thereafter renders itself inactive following ignition of the lamp. In accordance with another aspect of the present application, a method of starting a lamp includes receiving a bus voltage signal, converting the bus voltage signal into an alternating current signal, preheating the lamp to an ignition temperature, igniting the lamp and inactivating the preheating after the lamp has been ignited. In accordance with another aspect of the application, provided is a method of igniting an auxiliary lamp, including detecting a conductive state of a main lamp in a lamp ballast circuit, the detecting being by a switch that controls preheating of the main lamp.

Abstract: The invention relates to a novel ballast device for pre-heating, starting and operating at least one UV emitter, constructed in the form of a gas discharge lamp with two heating coils lying opposite each other in relation to a gas discharge path, whereby four electrical connections are provided in total for each of such gas discharge paths, namely two for each heating coil. According to the invention, switching means are provided for a parallel switching of both of said connectors of a heating coil, dependent upon operating conditions. A capacitive loading of the ballast device is thus avoided by means of the otherwise open connector line for the heating coil and the current feed to the coils is evenly distributed.

Abstract: The object of the present invention is to provide a flash lamp unit with a long service life which allows a high radiant efficiency to be obtained and a flash radiation device demonstrating excellent flash radiant performance despite a small size, and the flash lamp unit comprises a flash lamp having mercury sealed in a discharge container, wherein preheating means is provided for preheating the flash lamp, the quantity of contained mercury in the flash lamp is in the range of 0.2 to 55 mg/cm3, and the flash lamp is ignited under the specified conditions, and the flash radiation device comprises the above-described flash lamp as a light source.

Abstract: A display device which is suitable for connection to a computer etc. allows an operator to freely set a power saving mode to suppress the wasteful consumption of power. Power reduction means reduces, in a plurality of modes, the power supplied to device components included in the display device. Power management output selecting means sets any of the plurality of modes on the basis of a selection made by an operator. Signal detecting means monitors horizontal and vertical synchronizing signals sent from a computer and detects as a trigger signal a state in which at least one of them is not being received. In response to the trigger signal being detected, power management signal output means gives an instruction to the power reduction means to perform the set mode.