Abstract: A control unit stores a count value, which is used to detect an operational position of a roof glass, in a RAM. The control unit determines whether the count value is properly stored in the RAM when a voltage of a power supply falls below a predetermined voltage and thereafter returns to the predetermined voltage. Even in a case where the control unit determines that the count value is properly stored in the RAM, the control unit determines there is a possibility of having a deviation between an actual operational position of the roof glass and the count value. Thereafter, the control unit resets a reference point of the roof glass.

Abstract: The present invention is a driving circuit for a DC brushless fan motor, comprising a control unit, a motor, a Hall element, a signal output unit, a temperature control circuit, a reverse protection circuit and a counter-electromotive force (CEMF) removal circuit, as tied in with a plurality of resistors, capacitors, diodes and transistors. Accordingly, the ambient temperature is sensed by the temperature control circuit and is fed back to control the rotation rate of the motor.

Abstract: The object of the invention is to inhibit the axial displacement caused by the insufficiency of a control response angular frequency of a frequency arithmetic unit of a synchronous motor and realize high-precision torque control also in acceleration/deceleration. To achieve the object, the axial displacement of the synchronous motor caused by the insufficiency of the control response angular frequency of the frequency arithmetic unit is estimated in consideration of the control response angular frequency and input ??c3 (=??c1+??c2) including an estimated value ??c2 in addition to an axial displacement operated value ??c1 to the frequency arithmetic unit is acquired. Hereby, even if the frequency arithmetic unit has an insufficient control response angular frequency, the quantity of axial displacement which will be caused by the insufficiency is estimated as a second axial displacement signal ??c2, is added and input.

Abstract: A starting circuit for an induction motor is provided whereby a stationary rotor flux is established then a stored charge supplied to a motor winding in order to provide a starting torque. Before applying a mains power supply to the motor after the starting torque has been applied, a back EMF is sensed, directly or indirectly, to provide an indication that the rotor is turning before the mains supply is connected to the motor. This provides a reliable and simple method for ensuring that a mains supply may be safely connected to the motor.

Abstract: Circuits and methods for use with an integrated circuit chip having internal back EMF estimation to control a permanent magnet synchronous motor includes an AC current feedback circuit, a scaling circuit, and a current regulator. Additionally, a speed regulator may be employed. In one embodiment, during operation at very low speed, the speed regulator is in an open loop control mode due to a back EMF detection limitation of the IC chip, and only the current regulator is active. A feedback current signal, together with a user-defined command current signal, serves the input of the current regulator, which controls the AC motor current and drives the motor speed from standstill. Once the motor speed reaches a certain level, the measured back EMF from the IC chip is sufficient to estimate the motor speed, which is compared with a user-defined command speed, and an error of the these two signals provides the input of a speed regulator.

Abstract: The object of the present invention is to provide a vehicle drive system which enables setting of appropriate start-up torque and restraining of progress of battery deterioration. A vehicle drive apparatus having an electric motor, which is driven with electricity supplied by a battery, for driving a vehicle or assisting it while driven by an engine includes: a temperature sensor for detecting the battery temperature, an discharge power upper limit setting means for setting an upper limit for discharge power of the battery depending on the battery temperature, a discharge power computing means for computing battery discharge power, a revolution speed sensor for detecting a revolution speed of the engine, a basic start-up torque setting means for setting basic start-up torque requirement depending on the revolution speed and a start-up torque adjust means for decreasing the start-up torque requirement if the discharge power exceeds the discharge power upper limit during engine start-up.

Abstract: Methods and apparatus permit: monitoring a level of a power source that provides operating power to a control circuit, the control circuit being of a type that senses signals in windings of a polyphase motor to maintain synchronization therewith; and converting kinetic energy of the polyphase motor into operating power for the control circuit when the level has fallen below a threshold level, such that the control circuit is capable of maintaining synchronization with the polyphase motor.

Abstract: A device for position determination in a sensorless direct current motor has a plurality of inductivities arranged in corresponding phases and inducing alternating voltages in a motor windings, a plurality of resistances located in phase branches to be evaluated for a position determination of a rotor position of the sensorless direct current motor, and a plurality of comparator components each associated with the corresponding phase branch to be evaluated.

Abstract: A method of reducing torque ripple and noise for an brushless DC machine comprising: determining a control frequency for the electric machine, the control frequency indicative of an existing current command to and a rotational velocity of the electric machine; multiplying the control frequency by a selected multiple and forming a modulating signal responsive thereto; and formulating a modified command profile. The method also includes: correlating and synchronizing the modified command profile with the existing current command and a rotor position for the electric machine; and generating a modulated current command to the electric machine.

Abstract: A method and system for determining the commutation position in a DC machine using a single-bit rotor sensor and the back EMF signal from a stator winding by calculating a delay value, which is equal to the time elapsed between detection of the position signal and the back EMF signal, and establishing commutation after a period of time equal to the delay value has elapsed from when the position signal is detected.

Abstract: Methods and circuits detect operational information about DC fans powered by pulse width modulation, such as detecting fan presence in a device and/or detecting rotational speed. Output pulses produced by the fan related to the rotational speed are utilized to produce temporary reductions of voltage at the input of a control circuit. The control circuit may count the temporary reductions per unit of time to detect the speed. A pull down resistor may be coupled to the input to pull the input to a continuously low voltage when the DC fan is not present to otherwise provide a pull up at the input, and the control circuit may detect a missing fan from the continuously low voltage. Additionally, or alternatively, a secondary voltage may be provided to the DC fan in addition to the pulse width modulation while a consistently high voltage is provided to the input of the control circuit.

Abstract: A local oscillator and logic circuit pulses the open winding of a brushless DC motor at start up and the back EMF is used to generate a voltage to boost the voltage available to the control circuit for optimizing performance when starting with low supply voltage. As the rotor of a motor rotates and the windings are commutated by the drive electronics there is generated in each winding a voltage caused by the collapse of the current and the inherent inductance of the winding. These voltages exceed the normal operating voltage of the motor. The energy in these voltages is used to generate a regulated power feed to the analogue circuitry of the control circuit at a suitable voltage level. During steady state conditions, when the motor is running, the commutation of the windings is continual and there is ample energy available to power analogue electronics, and, if required, associated digital electronics as well.

Abstract: A constant flow of air through a personal air sampler is provided regardless of changes in the air flow path, by altering the pump speed as a function of the power taken by the pump. The characteristics of the pump are precalibrated to provide a constant used together with the square of the voltage appearing across the motor armature coils (applied voltage minus back Emf), which reflects the power currently used, to adjust the motor speed and thus provide a constant flow of air under changing conditions of resistance.

Abstract: A fan motor includes a rotor coil and a stator coil. The stator coil has its starting coil or rotating coil provided with an auto-coupling tapped coil or a third coil to make up a secondary coil of the starting coil or the rotating coil. The tapped coil or the secondary coil is coupled to produce a voltage value to be supplies as power for a DC motor for the swinging head of an electric fan, or power for a stabilized and rectified circuit, able to economize producing cost and supply the fan motor with a large current.

Abstract: In a motor driving device that drives a motor by energizing a coil of a first phase and a coil of a second phase provided in the motor in one direction alternately, which phase to energize is switched according to a back electromotive force appearing in the coil of each phase of the motor as a rotor of the motor rotates. This circuit configuration eliminates the need for an external sensor to detect the position of the rotor, and thus helps promote cost reduction and miniaturization. Here, where no external sensor is used to detect the position of the rotor, the motor is started by first bringing the rotor to rest in a particular position and then energizing the coil of a particular phase. This permits the motor to be started always in the same rotation direction, and thus helps prevent reverse rotation of the motor.

Abstract: In start-up control of a motor in which currents are caused to flow through any two of three phase coils to detect the polarity of a voltage induced in each de-energized phase, thereby determining the corresponding energized phase at start-up thereof, based on the polarity of the detected induced voltage, the levels of induced voltages are detected in addition to the polarity of the induced voltage for the de-energized phase to thereby determine the relationship between the magnitudes thereof, and the energized phase at the start-up is determined based on the relationship of magnitude between the polarity of each induced voltage and the level thereof.

Abstract: A device for controlling a motor intended to set an arm provided with a head for reading/writing information in motion with respect to a surface carrying information. The device having a controller for enabling the power supply of the winding of the motor to be managed and a measurer for measuring the value of a counter-electromotive force induced in the winding by the movement of the rotor when the power supply of the winding is interrupted. This device enables the angular speed of the arm to be measured and controlled during an emergency return phase of the arm towards a rest position.

Abstract: The present invention provides a method for shifting the instant of commutation for a sensorless and brushless direct-current motor (1), whose stator windings are fed by a multi-phase converter connection. The converter connection includes an output stage control (2), a commutation logic (3), a phase selector (4), and phase discriminator (5). A commutation detection (6) is supplied at one input (46) with the instantaneous value of the voltage induced in a phase, the instantaneous value being determined by the phase selector, and at a second input (47), with a reference voltage (Uref) for comparison. The reference voltage (Uref) can be changed by a commutation shift (7) in correspondence with a specific characteristic curve (71). A manipulated variable (Ust) is supplied by a manipulated-variable calculation (8) to the commutation shift (7) as a function of the setpoint speed (Nsetpoint) of the motor. The commutation shift takes place in an advantageous manner in a parabola shape.

Abstract: A motor controller system comprises solid state switches for connection between an AC line and motor terminals for controlling application of AC power to the motor. A sensor senses AC line voltage. A control circuit controls operation of the solid state switches. The control circuit ramps switch current during a start mode and selectively holds switch current during the start mode if sensed voltage drops below a threshold amount.

Abstract: An electric system utilizes dynamic impedance changes in windings of an electric motor to measure/monitor mechanical position. The method employs a bridge amplifier to measure voltage at a center node or windings against a voltage derived from a reference network. When a winding of the motor is driven, the winding forms a voltage divider across the center node. Impedance changes in windings occur as rotor poles pass by stator poles. The center node voltage varies with these impedance changes in legs on either side; this variation with respect to the reference network corresponds to measurement of rotational position. These measurements provide position/velocity feedback to a servo controller as long as current runs through a winding. This position sensing also applies to controlling commutation for brushless DC motor. Impedance measurement use normal motor-drive current for excitation without additional sensing signals, extra “sense” windings, or external sensors.

Abstract: A method for setting an electric motor, which includes, during a non-powering sequence of at least one of the motor phases, measuring on a predetermined time window, the induced voltage (Ti) in the non-powered phase and in comparing its mean value to a threshold value (Ts) to stop powering of the motor on the current sequence if the measured mean value is less than the threshold value.

Abstract: A method for electronically commutating a motor having a plurality of phase windings associated therewith is disclosed. In an exemplary embodiment, the method includes sensing a back electromotive force (BEMF) generated by each of the phase windings, and scaling the magnitude of the sensed BEMF values for each of the phase windings to a normalized value to produce gain corrected BEMF signals. The gain corrected BEMF signals are then used to determine a rotor position of the motor.

Abstract: Method and apparatus for initializing a disc drive to bring a spindle motor to a final, operational velocity after a disc drive processor reset condition. The spindle motor is rotated using electronic commutation and back electromotive force (bemf) detection. Upon initialization of the disc drive, a control circuit checks for the presence or absence of detected bemf. The absence of bemf indicates the spindle motor is either at rest or is rotating at a relatively low velocity. In the absence of bemf, the electrical rotational position of the spindle motor is determined, a short braking pulse is applied to the motor, and rotation of the spindle motor is detected in relation to changes in the electrical rotational position. Further breaking pulses are applied until no apparent change in electrical rotational position is detected, after which the spindle motor is accelerated from rest to the final, operational velocity.

Abstract: A method and apparatus are disclosed for controlling the operation of a multiphase motor, and particular to spinning the motor from an inactive state to an operable state. The method and apparatus include initially sensing an electrical characteristic of one or more phase windings, such as performing an inductive sense operation. Having sensed values of the electrical characteristic, a determination is made as to whether or not the motor's rotor is spinning. Upon a determination that the rotor is not spinning, a spin-up operation is performed to bring the spin of the rotor to operable spin speeds. On the other hand, upon a determination that the rotor is spinning, a resynchronization operation is performed to synchronize the application of drive signals for the phase windings of the motor to the dynamic position of the rotor.

Abstract: An electronic system utilizes dynamic impedance changes in windings of an electric motor to measure/monitor mechanical position. The method employs a bridge amplifier to measure voltage at a center node of driven motor windings against a voltage derived from a reference network. When a winding of the motor is driven, the winding forms a voltage divider across the center node. Impedance changes in windings occur as rotor poles pass by stator poles. The center node voltage varies with these impedance changes in legs on either side; this variation with respect to the reference network corresponds to measurement of rotational position. These measurements provide position/velocity feedback to a servo controller provided that some current is running through a winding. This position sensing also applies to controlling commutation for brushless DC motor. Impedance measurements use normal motor-drive current for excitation without additional sensing signals, extra “sense” windings, or external sensors.

Abstract: A system and method of advancing the commutation sequence of a brushless DC motor is provided. The motor having a plurality of coils, each of the coils coupled together at one end to a common center tap and coupled at an opposite end, through a respective coil tap, to both a source voltage and ground via selectively actuateable switches having diodes coupled in parallel therewith. The motor operates in a pulse width modulation (PWM) mode having PWM-on states and PWM-off states. During PWM-off states, a coil tap voltage from the coil tap of a floating phase is provided to a preconditioning circuit. The preconditioning circuit adjusts the floating phase coil tap voltage to compensate for an amount of voltage substantially equal to an amount of voltage by which a voltage at the center tap deviates from zero. The preconditioning circuit further includes sharpening circuitry for amplifying the adjusted floating phase coil tap voltage.

Abstract: A apparatus for controlling an actuator including, an integrator circuit to generate an integrated signal to be represented by a back EMF voltage, a amount circuit to generate a amount signal to indicate the amount to raise or lower the integrated voltage, a direction circuit to generate a direction signal to raise or lower the back EMF voltage, a comparator circuit to compare said integrated voltage with the back EMF voltage, and a switch circuit to add and subtract the amount signal with the integrated voltage in accordance with the direction signal.

Abstract: The system provides for the commutation of a brushless direct-current motor. A virtual star is provided that is analogous to the motor. The virtual star is formed of resistors. A comparison device continuously comparing the voltages of the two star center points of the motor star and the virtual star in all phases. The comparison results are used to generate a signal for controlling the commutation.

Abstract: A sine wave filter including an inductor for each phase (three inductors) and three delta- or Y-connected capacitors is employed within a borehole power system, coupled within a three phase power system at the surface between the output of a variable frequency drive and a three phase power cable transmitting power to a borehole location, and boosts the output voltage of the drive. The sine wave filter is designed to have a resonant frequency higher than the maximum operational frequency of the drive, and a Q such that, at the maximum operational frequency of the drive, the filter provides a voltage gain equal to the ratio of the desired voltage to the drive's maximum output power at the maximum operational frequency. The sine wave filter also smooths the voltage waveform of a pulse width modulated variable frequency drive.

Abstract: A motor drive circuit for driving a brushless motor having a rotor and exciting coils of respective phases. A square wave rotor position signal for each phase is produced wherein a half period of the rotor position signal corresponds to a time period from a polarity inversion of an induced voltage of the exciting coil to the next polarity inversion of the induced voltage. Based on the rotor position signal, excitation of the exciting coils is performed by controlling switching elements for conducting excitation currents by using square wave on-control and/or pulse width converted square wave pulse width modulation (PWM) control. A pulse width converted sinusoidal wave PWM signal is generated whose pulse width varies according to a sinusoidal function. Excitation of the exciting coils is controlled based on the pulse width converted sinusoidal wave PWM signal immediately before and after the square wave on-controlled portions and/or the pulse width converted square wave PWM controlled portions.

Abstract: An exemplary embodiment of the invention is a method for torque control of a PM synchronous machine. The method includes obtaining a torque command signal and a machine speed and determining an operating mode in response to the torque command signal and the machine speed. The operating mode includes a first operating mode and a second operating mode. In the first operating mode, a stator phase voltage magnitude is computed and an angle between the stator phase voltage and a stator phase back emf is determined in response to the stator phase voltage magnitude. In the second operating mode, the stator phase voltage is set to a predetermined magnitude and the angle between the stator phase voltage and the stator phase back emf is determined in response to the predetermined magnitude.

Abstract: An apparatus for parking a read/write head during power interruptions and methods of operating the same result in a hard disk drive apparatus that reduces the time to steady state the operating hard disk drive. The apparatus for reducing the time to steady state the operating disk drive having an actuator arm coupled to a voice coil for latching the actuator arm when power is interrupted comprises a Y-winding spindle motor having a first winding, a second winding, and a third-winding, and a spindle motor controller coupled to the Y-winding spindle motor configured to dynamically short the first winding and the second windings to produce a retarding force against the Y-winding motor and to direct power produced by the third winding in series with the first two windings in parallel to the voice coil for moving the actuator arm to a latched position and to maintain sufficient power to the spindle motor to provide greater operating range (headroom).

Abstract: The present invention proposes a method of detecting reverse rotation of a DC motor by using the back EMF, wherein the back EMF of the DC motor is detected to judge whether the brakeage of the motor is finished. A simple electronic circuit is exploited to accomplish this work effectively. No additional sensors are required so that the cost can be reduced.

Abstract: A back EMF monopole motor and method using a rotor containing magnets all of the same polarity and in a monopole condition when in momentary apposition with a magnetized pole piece of a stator having the same polarity, said stator comprised of a coil with three windings: a power-coil winding, a trigger-coil winding, and a recovery-coil winding. The back EMF energy is rectified using a high voltage bridge, which transfers the back EMF energy to a high voltage capacitor for storage in a recovery battery. The stored energy can then be discharged across the recovery battery through the means of a contact rotor switch for further storage.

Abstract: The invention provides an motor drive apparatus comprising a detector for detecting a terminal voltage in a non-energized phase and a detector for detecting a DC voltage applied to the main line of an inverter. The rotation of the brushless motor is controlled by specifying the inverter circulating current period from the terminal voltage and the DC voltage and calculating the magnetic pole position of the rotor from the terminal voltage after the end of the inverter circulating current period and a waveform of the terminal voltage predetermined from the characteristics of the brushless motor. As a result, the brushless motor can be rotated stably throughout a wide revolution range from low to high speeds.

Abstract: A hybrid vehicle includes an engine and a motor disposed therein as a vehicle-propelling system, the motor being connected to an output shaft and having both driving and power-generating functions. The vehicle includes an engine control apparatus which controls a running state of the engine and a motor control apparatus which controls both driving and power-generating states of the motor to be independent from the control of the engine by the engine control apparatus. The motor control apparatus functions to detect an open-circuit voltage of a main battery at motor driving stop and to set an upper limit-determining voltage and a lower limit-determining voltage for motor driving according to the main battery open-circuit voltage. As a result, by the control apparatus, an over-charge and an over-electric discharge of the main battery can be prevented, and it is possible to extend battery life.

Abstract: In a motor driving device that drives a motor by energizing a coil of a first phase and a coil of a second phase provided in the motor in one direction alternately, which phase to energize is switched according to a back electromotive force appearing in the coil of each phase of the motor as a rotor of the motor rotates. This circuit configuration eliminates the need for an external sensor to detect the position of the rotor, and thus helps promote cost reduction and miniaturization. Here, where no external sensor is used to detect the position of the rotor, the motor is started by first bringing the rotor to rest in a particular position and then energizing the coil of a particular phase. This permits the motor to be started always in the same rotation direction, and thus helps prevent reverse rotation of the motor.

Abstract: A disk drive comprising a disk having a data area, a head, a spindle motor for spinning the disk, and an actuator for positioning the head over the data area during a spindle speed control mode, and retracting the head away from the data area during a spindle speed fault mode is disclosed. A servo microprocessor executes steps of a servo control program to generate a first control signal. An actuator driver circuit is responsive to the first control signal for controlling the actuator during the spindle speed control mode. A spindle speed detector generates a spindle speed signal representing a spin rate of the spindle motor, and a spindle speed fault detector is responsive to the spindle speed signal for detecting the spindle speed fault mode and generating a second control signal in response to the detected spindle speed fault mode.

Abstract: The present invention herein relates to a driving control apparatus of motorized scooter comprised of battery, driving unit, and motor, characterized in which the driving unit consists of at least a relay, a start-up and protective circuit, an under-voltage protective circuit, a power switch and speed control circuit, and a braking unit, that when the power switch and speed control circuit are on, and the relay is open, user may push the wheels of the scooter manually to drive the motor; when a set speed is reached and the relay is closed, the motor is driven directly, controlling the speed of the scooter, in addition, when the speed of the scooter is below a certain rate, the relay will be opened to stop the motor; at this time, the user may restart the motor by pushing the wheels of the scooter manually to move the scooter forward.

Abstract: A motor controlling semiconductor integrated circuit for controlling a motor by a PLL control is provided comprising output transistors for driving a motor, a position detecting means detecting a rotational position of a rotor in said motor, for generating a position detection signal, a phase comparing means comparing said position detection signal with a reference clock, for generating a phase difference detection signal, and means receiving said phase difference detection signal, for controlling an on-duty of said output transistors on the basis of a duty of said phase difference detection signal.

Abstract: An electric machine drive system uses an estimation of the DC bus voltage to improve machine drive control. The DC bus voltage is estimated by injecting a carrier signal into the machine drive and determining the magnitude of the positive sequence current component induced in the drive by the carrier signal. The measured magnitude of current may be referenced to the anticipated magnitude of the current in order to produce an inverse value of the estimated DC bus voltage that is then used to normalize the commanded voltage signal driving the machine. Alternatively, a look-up table is used to relate the measured magnitude of the current component to a corresponding estimated value of the bus voltage.

Abstract: The present invention is a motor control device for controlling current command values in relation to a permanent magnet reluctance motor which generates torque corresponding to the combined value of the torque resulting from the permanent magnet and the reluctance torque through field-weakening control in such a manner that the motor terminal voltage does not exceed the maximum inverter output voltage. In particular it controls the angle of the current relative to the motor rotor which is required for the purpose of field-weakening control, and ensures that this is stable and effective whatever torque is output.

Abstract: Disclosed is control circuitry for providing controlling a motor responsive to feedback signals. The control circuit includes a velocity sensor for coupling with the motor for providing a velocity feedback signal responsive to the velocity of the motor, and circuitry for providing a feedback signal responsive to a voltage associated with the motor, such as the back emf of a coil associated with the motor. The control circuitry can be used enhance the Z-axis control of a tool of a work apparatus for performing work operations on a work material, such as a cutting apparatus for cutting a sheet of vinyl having a releasable backing for generating graphic products.

Abstract: A movable barrier operator having improved safety and energy efficiency features automatically detects line voltage frequency and uses that information to set a worklight shut-off time. The operator automatically detects the type of door (single panel or segmented) and uses that information to set a maximum speed of door travel. The operator moves the door with a linearly variable speed from start of travel to stop for smooth and quiet performance. The operator provides for full door closure by driving the door into the floor when the DOWN limit is reached and no auto-reverse condition has been detected. The operator provides for user selection of a minimum stop speed for easy starting and stopping of sticky or binding doors.

Abstract: A method to trim a monitor circuit for a voice coil motor including the steps of transmitting a test current through a voice coil motor, determining if a linear response is generated by the monitoring circuit, trimming the monitoring circuit if a non-linear response is received; repeating said transmitting step, said delivery step and said trimming step until said trim is achieved.

Abstract: The invention relates to an electric drive device with a DC motor (2) comprising a control circuit with an electronic commutator (3). The invention is characterized in that a derivation of a control signal (V_i_ref) is obtained from an induced motor voltage (E_sample) detected by a measuring device and from a reference value (V_i_av) which serves to regulate the speed of the DC motor (2), and in that the derived control signal (V_i_ref) serves to achieve a substantially constant torque of the DC motor (2) through adjustment of the motor currents (ia, ib, ic).

Abstract: The invention relates to a device for controlling a motor CM intended to set an arm MA provided with a head for reading/writing information MRH in motion with respect to a surface carrying information HD.

Abstract: The method is for controlling a voice coil motor which drives a mechanical arm via a control circuit which sets the output nodes, to which the motor is connected, in a high impedance state for a certain time interval. The method and circuit detect the back electromotive force induced on the motor winding during the time interval, and deliver current pulses for driving the motor. The circuit compares the detected back electromotive force with a certain target value and regulates the amplitude of the driving current pulses as a function of the difference between the detected value of the back electromotive force and a voltage signal representing the desired speed of the arm, according to a pre-established function. A preferred embodiment includes such a function being a pre-established saturated linear characteristic with an offset value.

Abstract: A circuit for providing commutation control signals to a commutator for a polyphase brushless dc motor in a mass data storage device includes an accumulator (48) to accumulate a digital count that is proportional or related to a phase difference between the commutation control signals and a motor bemf. A digital variable frequency oscillator (52) generates an oscillator output signal of frequency proportional to the digital count to reset the accumulator (68) after a predetermined time determined by the frequency. The circuit may also include a digital filter (50) between the digital accumulator (48) and the digital variable frequency oscillator (52) to generate a magnitude signal (DRC) of magnitude proportional to the accumulated count for delivery to the variable frequency oscillator (52) to control the frequency thereof.

Abstract: In a motor driving device, the currents supplied from a driver (3) to three-phase coils (2) of a motor are made to flow through a resistor (R), and the voltage appearing across this resistor (R) is fed to the positive input terminal of a current limiting circuit (8). The differential signal between this voltage and a voltage (V) fed to the negative input terminal of the current limiting circuit (8) is fed as a voltage signal to an OR circuit (9). Also an FG signal produced by a logic circuit (5) to represent the rotational speed of the motor is fed, through a speed discriminator (6) and a filter (7), as a voltage signal to the OR circuit (9). The OR circuit (9) feeds a voltage signal having a high level to a PWM comparator (11), which produces a PWM signal and feeds it to the logic circuit (5). Thus, when the currents supplied to the three-phase coils (2) are about to exceed a limit, the currents are limited so as not to exceed the limit by the voltage signal output from the current limit circuit (8).