Abstract: Soft start systems for electrically powered tools are described. The soft start systems use direction feedback signal(s) from a direction selection switch of the power tool. Also described are power tools using such soft start systems. In addition, electrical power circuits using the soft start systems are described.

Abstract: A DC-powered system may include controls configured to switch between available DC power supplies and manage the refrigeration system in accordance with one or more methods. The one or more methods of the control system may include multiple tiers of power management, including, e.g., maximization of power usage when on a photovoltaic power supply to subcool a refrigerated load.

Abstract: A remote monitoring system and a method of operating a system having a pump is provided. The remote monitoring system includes a vacuum/pressure sensor coupled to measure a vacuum or a pressure in the system. A temperature sensor is positioned to measure an ambient temperature. A fluid level sensor is positioned to measure fluid in a collection tank. A controller is operably coupled to the vacuum/pressure sensor, the temperature sensor and the fluid level sensor, the controller having a communications circuit that is operable to transmit and receive signals via a cellular SMS text message communications medium, the controller having one or more processors that are responsive to nontransitory executable computer instructions, the one or more processors being responsive to change the operation of the pump in response to an operating signal from the communications circuit, the temperature sensor or the vacuum/pressure sensor or the fluid level sensor.

Abstract: Embodiments of a method, controller and system include an electric generating system with interleaved direct current DC-DC converter are provided. The embodiments include a controller, a permanent magnet generator (PMG), wherein the PMG provides a 6-phase PMG, and a rectification stage coupled to the PMG. The embodiments also include a boost converter stage coupled to the rectification stage, wherein the boost converter stage comprises four phases, a DC link capacitor coupled to the boost converter stage, and an output filtering stage coupled to the DC link capacitor.

Abstract: An apparatus for detecting device types of storage devices may include (1) at least one circuit that (A) is electrically coupled to a power supply and (B) when a storage device is connected to the power supply, outputs a signal that is indicative of a device type of the storage device, (2) at least one physical processing device that (A) is electrically coupled to the circuit, (B) detects the signal that is output by the circuit when the storage device is connected to the power supply, (C) determines the device type of the storage device based at least in part on the signal output by the circuit, and then (D) directs the power supply to supply power to the storage device in accordance with the device type of the storage device. Various other apparatuses, systems, and methods are also disclosed.

Abstract: An interface circuit having releasable electrical connectors and as little as a single relay providing a standardized connection between panel controls intended for three-wire, two-wire or combination three-wire/two-wire control and a motor drive or motor controller. In this way, greatly simplified manufacturing of control cabinets may be provided with variations in control strategy being implemented simply by the provision of different panel controls having prewired harnesses and connectors.

Abstract: Disclosed is a motor-driven vehicle including: a first and second battery; a voltage converter that includes a plurality of switching elements configured to perform voltage conversion between an electric power output path and the first and second battery, and to switch the connection of the first battery and the second battery between an in-series connection and an in-parallel connection; a motor-generator; and a control device configured to turn on and off the switching elements, in which the control device switches connection to either of connection between the electric power output path and both the first battery and the second battery, and connection between the first battery and the second battery based on the switching element temperature, and the operating point of the motor-generator.

Abstract: An electric submersible pump (ESP) control system includes a primary variable frequency drive (VFD), a transformer, and a secondary VFD. The primary variable frequency drive (VFD) is configured to receive power from a power source and output a variable voltage and variable amplitude AC voltage. The transformer has a low voltage side and a high voltage side of the transformer. The primary VFD is coupled to the low voltage side. The transformer is configured to receive the AC voltage from the primary VFD and output a stepped up AC voltage. The secondary VFD is coupled to the high voltage side of the transformer, wherein the secondary VFD is configured to provide a supplemental voltage in addition to the stepped up AC voltage when the operational values of an electric motor exceed a threshold value.

Abstract: A voltage regulator includes a pass unit configured to transfer an input voltage to an output node as an output voltage according to a control signal, a voltage dividing unit configured to divide the output voltage to generate a divided output voltage, an error amplifying unit configured to output a comparison signal based on comparing a magnitude of the divided output voltage with a magnitude of a reference voltage, and a filter unit configured to filter noise included in the outputted comparison signal to generate the control signal. The filtered noise can correspond to noise included in the outputted comparison signal by transferring noise included in the input voltage to the error amplifying unit via the pass unit and the voltage dividing unit.

Abstract: An enclosure or shelter having an interior chamber for housing electronic components and equipment is provided with an HVAC/R system configured with a rechargeable DC power source for power back-up to maintain substantially uninterrupted power in the case of a main power failure. The system includes one or more variable frequency drives (VFD) controlled by a VFD controller and configured to provide three-phase power to one or more three-phase AC motors and single-phase power to one or more single-phase AC motors. The system also includes a power source controller configured to select and power sources based on availability of one or more power sources and other logic.

Abstract: An impact power tool includes a motor, a battery, a hammer mechanism and a control apparatus. The motor runs in the same speed no matter what torque level is selected. The motor runs for a total running time which is identical to an impacting time plus a compensative time. The impacting time is decided according to the selected torque level, and the compensative time is decided according to the power of the battery. An impacting time table and a compensative time table are pre-established to decide the impacting time value and the compensative time value. Therefore, the impact power tool always provides the theory torque output of the selected torque even if the battery is low.

Abstract: A motor control device has a current value sampling unit configured to sample a current value of a motor, a PWM signal generation unit configured to generate a PWM signal to drive the motor, based on the sampled current value of the motor, and a power supply stop unit configured to stop supply of power from a control power supply to a peripheral depending on power stored in a DC link part and power to which the control power source can supply when an alternating-current power source fails.

Abstract: A PWM signal generation unit generates a PWM signal to drive a motor, based on a current value of the motor sampled by a current value sampling unit, a position or speed of the motor sampled by a motor sampling unit, and a position or speed of a driven object sampled by a driven object sampling unit. An operation stop unit stops the operation of any one of the motor sampling unit and the driven object sampling unit depending on the power stored in the DC link part and power to which the control power source can supply when the alternating-current power source fails.

Abstract: A motor drive device (1) of the present invention includes a converter unit (10) and an inverter unit (30). The converter unit (10) includes: power supply voltage monitoring unit (3) for detecting a power failure; DC link voltage detecting means (4); capacitor total capacity calculating means (6) which calculates total capacity of DC link smoothing capacitors (17, 18) and calculates a DC link low-voltage alarm detection level for an instantaneous power failure; DC link low-voltage alarm detection level setting means (8) which varies the DC link low-voltage alarm detection level for an instantaneous power failure as necessary; and alarm generating means (7) which monitors the DC link voltage and generates an alarm to protect the converter unit. In the case where a power failure is detected, the DC link low-voltage alarm detection level is increased in accordance with the total capacity of the DC link smoothing capacitors (17, 18).

Abstract: This disclosure is drawn to methods, systems, devices and/or apparatus related to power control in applications over long cables. Specifically, the disclosed methods, systems, devices and/or apparatus relate to power control that considers the maximum power available at the end of a long cable (or from a battery) to a load over a broad range of load conditions. Some example systems may include a power supply located at the Earth's surface and a power converter coupled to the power supply via a cable having a first end coupled to the power supply and a second end coupled to the power converter. Some example power converters may be configured to measure the power being consumed by the electrical load in the well, and adjust operating parameter(s) of the electrical load based, at least in part, on the maximum power available at the second end of the cable.

Abstract: A method of controlling a fan in a vehicle comprising: measuring a control input signal; measuring a continuous applied voltage to the fan; comparing the continuous applied voltage to a look up table; and activating the fan when the control input signal is open and the continuous applied voltage is greater than a system voltage by about 0.5 volts.

Abstract: A method for operating an ultracapacitor system used in a mining excavator powered by an electrical power source. The method includes the step of detecting whether a line power from the electrical power source is present. Next, a voltage level of the ultracapacitor system is measured if the line power is not present. The measured voltage level is then compared with a minimum voltage level for the ultracapacitor system. If the measured voltage level is more than the minimum voltage level, auxiliary power is supplied from the ultracapacitor system to operate mining excavator systems. The auxiliary power may be used to power electronic systems and components such as computers, displays, control systems, gas insulated switchgear and lighting systems.

Abstract: A load driving device according to the present invention has: an internal circuit (DRV) that operates in response to the supply of a power supply voltage (HV or LV); an output circuit (PD1 and PD2) for driving a load in response to the supply of the power supply voltage (HV or LV); an abnormality detection circuit (12) for monitoring the power supply voltage (HV or LV) and generating an abnormality detection signal (S1); and a power supply switch (P0) for, according to the abnormality detection signal (S1), conducting or cutting off a power-supply-voltage supply line to the internal circuit (DRV).

Abstract: A method and device for controlling the starting time of a vehicle mounted thermal engine coupled mechanically to a polyphase rotary electrical machine with an inductor. The electrical machine includes phase windings and sensors for the position of a rotor, and is connected to an on-board electrical network. The method uses pre-fluxing by establishing an excitation current in the inductor for a predetermined pre-fluxing time, before establishment of phase currents. These phase currents are controlled by signals phase-shifted by an angle which varies according to a speed of rotation of the electrical machine, relative to synchronization signals produced by the sensors. During the starting time, the angle of phase-shifting is additionally dependent on a voltage of the on-board electrical network, in a range contained between a first and second voltages, with the second voltage being higher than the first. In the method, the starting time is independent from the voltage of the on-board electrical network.

Abstract: A piston-type fuel pump is provided. The fuel pump includes a housing bounding an internal cavity with a cylindrical tube disposed in the internal cavity. The cylindrical tube provides a bore extending along an axis and a piston is disposed in the bore. A spring is configured to bias the piston in a first direction along the axis. A coil is disposed about the cylindrical tube and a control circuit is disposed in the internal cavity. The control circuit is configured in electrical communication with the coil. The voltage supplied to the control circuit can be varied, with the control circuit compensating for the variable supply voltage to regulate the actuation of the coil from a de-energized state to an energized state. The piston is biased in a second direction opposite the first direction in response to the coil being actuated.

Abstract: A motor driving apparatus includes: a threshold providing circuit that provides a plurality of power failure detection thresholds determined according to an installation environment of the motor driving apparatus, a selection circuit that selects a specified power failure detection threshold from the power failure detection thresholds, and a comparison and determination circuit that determines presence or absence of an occurrence of power failure by comparing a detected voltage of an alternating-current power input to a motor driving circuit and the selected power failure detection threshold. Consequently, it is possible to select the power failure detection threshold, which determines a detection reference of power failure in which alternating-current power input is interrupted, according to an installation environment, so that the abnormal end process in the case of an occurrence of power failure in which alternating-current power input is interrupted can be surely performed in any installation environment.

Abstract: Provided is an inverter control device that can detect momentary abnormality in a power-supply voltage for sure, and return quickly to regular state when the abnormality in the power-supply voltage has been settled. The inverter control device consists of a main power-supply (31); a sub power-supply (22) that converts electric power distributed from the main-power supply (31); a controller (21) that operates with a control power-supply supplied from the sub power-supply (22); a transistor (4) that makes the input signal of the controller (21) turn ON/OFF, by having the current between the emitter and collector made to turn ON/OFF; and a power-supply monitoring circuit (3) that is connected to the main power-supply (31) via at least a resistor (rD), and monitors the voltage of the main power-supply (31).

Abstract: Disclosed is a method of detecting the disconnection state of a power cable in an inverter system. The method includes detecting a battery voltage, detecting a DC-link voltage, detecting the disconnection state of the power cable based on a difference value between the detected battery voltage and the DC-link voltage, and stopping driving of a motor if the power cable is detected as being disconnected.

Abstract: A PWM signal generation unit generates a PWM signal to drive a motor, based on a current value of the motor sampled by a current value sampling unit, a position or speed of the motor sampled by a motor sampling unit, and a position or speed of a driven object sampled by a driven object sampling unit. An operation stop unit stops the operation of any one of the motor sampling unit and the driven object sampling unit depending on the power stored in the DC link part and power to which the control power source can supply when the alternating-current power source fails.

Abstract: A motor drive device (1) of the present invention includes a converter unit (10) and an inverter unit (30). The converter unit (10) includes: power supply voltage monitoring unit (3) for detecting a power failure; DC link voltage detecting means (4); capacitor total capacity calculating means (6) which calculates total capacity of DC link smoothing capacitors (17, 18) and calculates a DC link low-voltage alarm detection level for an instantaneous power failure; DC link low-voltage alarm detection level setting means (8) which varies the DC link low-voltage alarm detection level for an instantaneous power failure as necessary; and alarm generating means (7) which monitors the DC link voltage and generates an alarm to protect the converter unit. In the case where a power failure is detected, the DC link low-voltage alarm detection level is increased in accordance with the total capacity of the DC link smoothing capacitors (17, 18).

Abstract: A method and apparatus for improving the run duration of an electric motor powered by a battery pack is provided. The apparatus includes an electric motor having a rated motor voltage, a battery pack having an output voltage exceeding the rated motor voltage, and a motor controller which converts the output voltage to supply electrical power to the electric motor at a second voltage lower than the output voltage.

Abstract: A method of controlling a fan in a vehicle comprising: measuring a control input signal; measuring a continuous applied voltage to the fan; comparing the continuous applied voltage to a look up table; and activating the fan when the control input signal is open and the continuous applied voltage is greater than a system voltage by about 0.5 volts.

Abstract: Various embodiments of a motor controller are disclosed. In exemplary embodiments, the motor controller can be instructed to select an operational profile based on the duration of power loss. In an exemplary embodiment, the system comprises a battery or capacitor to provide power to a microcontroller in the motor controller while power is disconnected.

Abstract: A robotic device includes an electric motor in which a drive control circuit includes a driver circuit for intermittently supplying the magnetic coils with a supply voltage VSUP; a switching signal generating circuit that generates a switching signal supplied to the driver circuit; and a voltage setter that supplies a supply voltage control value Ya to the switching signal generating circuit. By adjusting pulse width of the switching signals DRVA1, DRVA2 with reference to the supply voltage control value Ya, the switching signal generating circuit adjusts the effective voltage which is applied to the magnetic coils.

Abstract: A converter and an inverter are connected via a clamp circuit. The converter performs commutation in accordance with any of a first commutation mode in which trapezoidal waves are compared with a carrier and a 120-degree conduction mode. A diode of the clamp circuit is short-circuited by a shorting switch. The shorting switch is rendered conductive when a power factor reduces or a power supply voltage reduces, and capacitors of the clamp circuit are connected in series between DC power supply lines. The converter performs commutation in accordance with the 120-degree conduction mode, not in accordance with the first commutation mode, while the shorting switch is conductive.

Abstract: A refrigerator and a method of operating the same are disclosed. In the refrigerator and the method of operating the same, a voltage of an electric power input is measured and rectified through the half wave rectification or the full wave rectification in correspondence with the measured voltage, so that the refrigerator can be used without a voltage converting device when a voltage of the input power is changed. Therefore, the change or the modification of the circuit is not needed in order to use the refrigerator in other regions. Since components are compatible and utility of the components is improved, manufacturing costs can be reduced.

Abstract: The invention relates to a safety controller for an actuating drive (2.1, 2.2, 2.3) for controlling a gas flow or a liquid flow in an open-loop or closed-loop manner by means of a flap (3.1, 3.2, 3.3) or a valve, in particular in the field of heating, ventilation, and air conditioning (HVAC) systems, fire-protection systems, and/or room protection systems. A safety circuit (9.1, 9.2, 9.3) is implemented to ensure the energy supply in a safety operating mode if an electricity supply circuit (8.1, 8.2, 8.3) drops off or is lost. A control value output circuit (1.1, 1.2, 1.3) detects status signals, in particular signals of a sensor (11.1, 11.2, 11.3), and/or status parameters of a system and/or a specifiable setting of an adjustment device that can be actuated manually. The safety control value is set to one of at least two different control values (SW1, SW2, . . . ) depending on the status signals so that the safety position of the flap is determined adaptively.

Abstract: A method and apparatus for improving the run duration of an electric motor powered by a battery pack is provided. The apparatus includes an electric motor having a rated motor voltage, a battery pack having an output voltage exceeding the rated motor voltage, and a motor controller which converts the output voltage to supply electrical power to the electric motor at the rated motor voltage.

Abstract: An electrical submersible pumping (ESP) system can include a pump located in a wellbore, a motor attached to the pump, a power source located at the surface, a cable electrically coupling the power source and the motor, and a current sensor. The ESP system can also include a controller communicating with the current sensor to calculate a voltage drop associated with the cable responsive to an impedance of the cable. The controller can also control a power source output voltage responsive to the calculated voltage drop. For example, the controller can adjust the power source output voltage to minimize a cable current while maintaining a minimum motor voltage. The controller can also control a motor shaft speed by changing a power source output voltage frequency to compensate for changing slip and adjust the power source output voltage to minimize the cable current while maintaining a minimum motor voltage.

Abstract: A hand-held, battery powered tool (e.g., nutrunner, drill) includes an output head operatively connected to a motor, a plurality of battery cells, an ON/OFF start switch, a resistance sensor that measures a resistance of the output head to movement, and a controller. When the start switch is ON and the resistance sensed by the resistance sensor does not exceed a predetermined shift resistance, the controller automatically connects the plurality of battery cells to each other and the motor in series. When the start switch is ON and the resistance sensed by the resistance sensor exceeds the predetermined shift resistance, the controller automatically connects the plurality of battery cells to each other in parallel and to the motor.

Abstract: An electric compressor control device includes: an inverter for electric compressor motor; a communication microcontroller arranged in a low-voltage region for transmission of an instruction signal via a high-speed communication bus; and a control microcontroller arranged in a high-voltage region and connected to the communication microcontroller via an insulation element for transmitting the instruction signal from the communication microcomputer as an inverter control signal to the inverter. The power voltage of the communication microcomputer is supplied from a low-voltage power source. The voltage from the low-voltage power source is transformed via a transformer and supplied as a power voltage of the control microcontroller.

Abstract: A method and apparatus is provided for controlling an electrical load exhibiting destabilizing negative-resistance negative-damping characteristics to provide positive damping of power grid oscillations and for controlling the electrical load to operate at a reduced power level when the power grid voltage is reduced.

Abstract: When a source consisting of series-connected battery 7 and auxiliary power supply 9 supplies an electric power to a motor 4, a MOS-FET 13 for preventing a current induced by a voltage of the auxiliary power supply 9 from being reversed upstream should be off if it operates normally. Therefore, voltages at the opposite terminals of the MOS-FET 13 should have a difference which corresponds to a voltage of the auxiliary power supply 9. Hence, the voltages at the opposite terminals of the MOS-FET 13 are detected by two voltage detectors 23 and 25 when the electric power from the auxiliary power supply 9 is supplied to the motor 4. If the potential difference between the voltages at the opposite terminals of the MOS-FET 13 is equal to or less than a predetermined value, a control circuit 24 issues a failure signal upon determination that the MOS-FET 13 suffers a short-circuit fault. A MOS-FET 15 is also monitored in the same way.

Abstract: A method for determining the magnet temperature of a permanent magnet electrical machine. The magnet temperature is able to be determined particularly simply and accurately if a phase voltage and the rotational speed of the electrical machine are measured, and the magnet temperature is determined from this.

Abstract: A method is disclosed for operating a rotating electric machine, wherein the rotating electric machine is connected by phases to a converter circuit having a direct-current circuit for switching at least two voltage levels, and the phases of the converter circuit are connected to the direct-current circuit according to a selected switch state combination of switch states of power semi-conductor switches of the converter circuit. Exemplary embodiments can reduce the switching frequency of the power semi-conductor switches, based on a prediction of further behavior of the overall system, and selection of an optimum switching state combination.

Abstract: A DC motor drive (100) including power electronics (120) and control electronics (130). The power electronics (120) are arranged to receive a high voltage power supply and to controllably output that supply to a DC motor to controllably operate the motor. The control electronics (130) are arranged to receive a low voltage power supply and to control operation of the power electronics (120) and hence of the motor at least partly in response to signals received by the control electronics (130) indicative of at least one potential difference across the power electronics (120). The drive further includes a microprocessor (150) and an opto-coupler (170) arranged to sense the output of the power electronics (120) and to generate based thereon the signals in a form for optical transmission via opto-coupler (170) between the output of the power electronics (120) and the control electronics (130), thereby allowing galvanic isolation of the control electronics (30) from the power electronics (120).

Abstract: A motor driving apparatus includes: a threshold providing circuit that provides a plurality of power failure detection thresholds determined according to an installation environment of the motor driving apparatus, a selection circuit that selects a specified power failure detection threshold from the power failure detection thresholds, and a comparison and determination circuit that determines presence or absence of an occurrence of power failure by comparing a detected voltage of an alternating-current power input to a motor driving circuit and the selected power failure detection threshold. Consequently, it is possible to select the power failure detection threshold, which determines a detection reference of power failure in which alternating-current power input is interrupted, according to an installation environment, so that the abnormal end process in the case of an occurrence of power failure in which alternating-current power input is interrupted can be surely performed in any installation environment.

Abstract: Provided is an inverter control device that can detect momentary abnormality in a power-supply voltage for sure, and return quickly to regular state when the abnormality in the power-supply voltage has been settled. The inverter control device consists of a main power-supply (31); a sub power-supply (22) that converts electric power distributed from the main-power supply (31); a controller (21) that operates with a control power-supply supplied from the sub power-supply (22); a transistor (4) that makes the input signal of the controller (21) turn ON/OFF, by having the current between the emitter and collector made to turn ON/OFF; and a power-supply monitoring circuit (3) that is connected to the main power-supply (31) via at least a resistor (rD), and monitors the voltage of the main power-supply (31).

Abstract: Various embodiments of a motor controller are disclosed. In exemplary embodiments, the motor controller can be instructed to select an operational profile based on the duration of power loss. In an exemplary embodiment, the system comprises a battery or capacitor to provide power to a microcontroller in the motor controller while power is disconnected.

Abstract: A motor control device has a plurality of drive circuits that are respectively provided on arms of an inverter circuit that supplies current to an AC motor, the plurality of drive circuits driving respectively a plurality of switching elements included on the arms; a power source control circuit that performs a control of a plurality of power supply circuits that supply power respectively to the plurality of drive circuits; a low-voltage circuit area that includes the power source control circuit; a plurality of high-voltage circuit areas, each high-voltage circuit area including a drive circuit from the plurality of drive circuits; and a plurality of transformers that serve as the plurality of power supply circuits and respectively join the low-voltage circuit area and the plurality of high-voltage circuit areas in an insulated state.

Abstract: The invention relates to a control method and system comprising an electronic control unit (11) controlling the electric current power supply from an electric power source to a motor-compressor arrangement (12, 13); the electronic control unit comprises a conversion means which is connected to an inversion means (15) to supply the voltage demanded by the motor (12). A PWM pulse width regulator (16) generates the switching signals for all the switching elements of the unit (11) relating to said demanded voltage.

Abstract: The present invention relates to a motor controller for air conditioner including a converter having at least one switching element for converter, the converter converting AC utility power into DC power by a switching operation of the switching element; an inverter having at least one switching element for inverter, the inverter converting the DC power into prescribed AC power by a switching operation of the switching element and driving a three-phase motor; a microcomputer outputting a converter switching control signal that controls the switching element for converter; and a dc terminal signal generator detecting a dc terminal voltage that is applied across an dc terminal of the converter to sequentially generate a pulse type dc terminal signal, and insulating the dc terminal from the microcomputer. The present invention may sequentially generate a dc terminal signal and simultaneously insulate the dc terminal from the microcomputer, thus making it possible to improve the stability of the motor controller.

Abstract: A main power supply and an auxiliary power supply for supplying power to a motor are provided. A MOS-FET for supplying power from the main power supply and a MOS-FET for supplying power from the main and auxiliary power supplies are provided. When a phenomenon in which a rotor of a motor is rotated by the going-back force of steered wheels occurs, and voltage VG of power generated by the motor satisfies the relation VG>VB+VC where VB is a voltage of the main power supply and VC is a voltage of the auxiliary power supply, a control circuit and a gate drive circuit turn off both MOS-FETs so as to charge the auxiliary power supply using the voltage VG through a parasitic diode of the MOS-FET.

Abstract: A method is specified for operating a rotating electrical machine, in which the rotating electrical machine is connected in terms of phase to a converter circuit, having a DC voltage circuit, for connecting at least two voltage levels, and the phases of the converter circuit are connected to the DC voltage circuit in accordance with a selected switching state combination of switching states for power semiconductor switches in the converter circuit. In order for operation of the rotating electrical machine to be possible in an event, over a number L of sampling times various values are determined, and a switching state combination is set as the selected switching state combination with which a sum of determined values is at its smallest.

Abstract: The drive control circuit (200) includes a driver circuit (250) for intermittently supplying the magnetic coils with a supply voltage VSUP; a switching signal generating circuit (240) that generates a switching signal supplied to the driver circuit (250); and a voltage setter (270) that supplies a supply voltage control value Ya to the switching signal generating circuit (240). By adjusting pulse width of the switching signals DRVA1, DRVA2 with reference to the supply voltage control value Ya, the switching signal generating circuit (240) adjusts the effective voltage which is applied to the magnetic coils.