Motor drive control circuit and motor apparatus using the same

A motor drive control circuit includes a rotation control amplifier that compares the lower of a voltage limiting reference voltage of a reference voltage source and a rotation speed control voltage, which controls the rotation speed of the motor, on a terminal with a peak voltage from an impedance element that detects a drive current of a motor. The motor drive control circuit further includes a rotation limiting comparator that compares a voltage that is substantially equal to the voltage limiting reference voltage with the peak voltage, a synthesis circuit that amplifies rotation position detection signals from the motor according to the output voltage of the rotation control amplifier, a PWM output comparator that compares the outputs of the synthesis circuit with a triangular wave voltage and outputs PWM signals, and a motor-driver control circuit that removes an output period of the rotation limiting comparator from the ON period of each PWM signal and controls a motor driver that drives the motor. The motor drive control circuit operates the elements defining the motor driver more in a safe operation region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor drive control circuit of a PWM (Pulse Width Modulation) control technique and also relates to a motor apparatus including such a motor drive control circuit.

2. Description of the Related Art

A motor apparatus using a conventional motor drive control circuit of a PWM control technique is shown inFIG. 4. A motor apparatus101shown in the figure includes a motor102, a motor driver107for driving the motor102, and a motor drive control circuit106for controlling the motor driver107.

The motor102includes a rotor109; coils LU, LV, LWof the U phase, V phase, and W phase for controlling the rotation of the rotor109; Hall elements HU, HV, HWfor detecting the position (phase) of the rotor109; and a rotation speed counter104for detecting the rotation speed of the rotor109. The motor driver107includes three output transistors TUU, TVU, TWUon the power source side and three output transistors TUL, TVL, TWLon the ground side. The motor drive control circuit106includes a current detection resistor112for converting a drive current of the motor102into a voltage; a peak hold circuit114for receiving this voltage and holding the peak voltage within the ON period of the below-described PWM signal; a rotation control amplifier113for inputting the peak voltage, the voltage limiting reference voltage of a reference voltage source123, and a rotation speed control voltage of a signal input terminal SIG, and comparing the lower of the voltage limiting reference voltage and rotation speed control voltage with the peak voltage; a capacitor122for oscillation prevention that is connected to the output of the rotation control amplifier113and has a capacitance of, for example, about 0.01 μF; a Hall amplifier116for inputting the Hall signals of the Hall elements HU, HV, HWand outputting the amplified signals; a synthesis circuit117for inputting the output of the Hall amplifier116, advancing each input by a constant phase (for example, 30°), conducting amplification at an amplification ratio corresponding to the output voltage of the rotation control amplifier113, and outputting the amplified signals; a triangular wave generator119for generating and outputting a triangular wave; a PWM output comparator118for comparing the polarity discrimination signals UHL, VHL, WHL, which are the outputs of the synthesis circuit117, as shown inFIG. 6, with the triangular wave and outputting PWM signals UPWM, VPWM, WPWM; and a motor-driver control circuit120for outputting to the motor driver107a control signal based on the PWM signals.

The detection output of the rotation speed counter104of the motor102is inputted to a motor control command unit (not shown in the figure) including a CPU. The CPU outputs a command signal (rotation speed control voltage) corresponding to the desired motor rotation speed to the signal input terminal SIG of the motor drive control circuit106. If the detection output of the rotation speed counter104is less than the desired motor rotation speed, the CPU increases the rotation speed control voltage so as to obtain the desired motor rotation speed. In such a case, the rotation control amplifier113increases the output voltage thereof since the rotation speed control voltage becomes higher than the peak voltage. Therefore, in the synthesis circuit117, the amplification ratio increases and the amplitude of the polarity discrimination signals UHL, VHL, WHLincreases. Then, the PWM output comparator118generates the PWM signals UPWM, VPWM, WPWMhaving a duty ratio with a large ON period and outputs to the motor driver107the control signals based on PWM signals via the motor-driver control circuit120. As a result, the drive current that is passed by the motor driver107to the coils LU, LV, LWof the U phase, V phase, W phase of the motor102increases and, therefore, the rotation speed of the motor102increases. Then, this drive current is converted into a voltage by the current detection resistor112, and the peak voltage thereof is compared with the rotation speed control voltage of the signal input terminal SIG, as described above. This loop operation is repeated and the peak voltage of the detection voltage is thereby matched with the rotation speed control voltage and stabilized.

Here, when an overload is applied to the motor102(referred to below as an abnormality), for example, when paper is jammed in the case where the motor102is used as a paper feed actuator of a copier, the detected rotation speed by the rotation speed counter104decreases. Therefore, the CPU increases the rotation speed control voltage according to the detected rotation speed in order to increase the rotation speed of the motor102. However, because the rotation speed of the motor102does not increase, this rotation speed control voltage rises too much. If the voltage limiting reference voltage of the reference voltage source123is exceeded, the voltage limiting reference voltage becomes lower and is, therefore, compared with the peak voltage. Thus, when the rotation speed control voltage rises too much, the excess increase of the drive current of the motor driver107flowing to the coils LU, LV, LWof the U phase, V phase, W phase of the motor102is prevented and damage to the elements is prevented (for example, see Japanese Patent Application Laid-open No. 2003-111481).

As described above, when the rotation speed control voltage from the CPU rises too much and exceeds the voltage limiting reference voltage of the reference voltage source123, the voltage limiting reference voltage, rather than the rotation speed control voltage, is compared with the peak voltage in the rotation control amplifier113. However, since the capacitor122for oscillation prevention that has a capacitance of about 0.01 μF is connected to the output of the rotation control amplifier113, the output thereof is delayed, a time is required for the output to be reflected in the synthesis circuit117, and a time is also required for the output to be reflected in the output of the PWM output comparator118and then in the rotation speed of the motor102, which is the final output.

FIG. 5shows a voltage waveform detected by the current detection resistor112in the case of an abnormality. The voltage E in the figure is a voltage limiting reference voltage of the reference voltage source123, and below this voltage is a region in which the elements defining the motor driver107are not damaged, that is, an element safe operation region. The amplitudes of polarity discrimination signals UHL, VHL, WHLinputted to the PWM output comparator118include an extra amount due to the above-described delay of the output of the rotation control amplifier113, the PWM signals UPWM, VPWM, WPWMcontaining an extra ON time period in the duty ratio are outputted from the PWM comparator118, and the motor driver107passes an extra drive current. Thus, in the conventional motor apparatus, a time period (for example, a time period shown by points A-B inFIG. 5) occurs in which the motor drive107operates above the element safe operation region. Furthermore, the power consumed in this period is wasted power.

As a countermeasure, an extra voltage that is due to the delay time caused by the capacitor122for oscillation prevention can be estimated and the voltage limiting reference voltage of the reference voltage source123can be set accordingly lower. However, because a load at the time of abnormality is not constant, the peak value of the voltage detected by the current detection resistor112varies, for example, as voltage C or voltage D shown inFIG. 5. Therefore, this countermeasure is actually difficult to use.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide a motor drive control circuit more capable of operating the elements defining the motor driver in a safe operation region.

The motor drive control circuit of a first preferred embodiment of the present invention includes a rotation control amplifier that inputs a peak voltage of a voltage generated in an impedance element for detecting a drive current of a motor, a voltage limiting reference voltage, and a rotation speed control voltage for controlling a rotation speed of the motor and compares the lower of the voltage limiting reference voltage and rotation speed control voltage with the peak voltage; a rotation limiting comparator that inputs and compares a voltage that is substantially equal to the voltage limiting reference voltage with the peak voltage; a synthesis circuit that amplifies a rotation position detection signal of the motor according to the output voltage of the rotation control amplifier; a PWM output comparator that compares an output of the synthesis circuit with a triangular wave voltage of a triangular wave generator and outputs a PWM signal; and a motor-driver control circuit that inputs the PWM signal and an output signal of the rotation limiting comparator, removes an output period of the rotation limiting comparator from an ON period of the PWM signal, and controls a motor driver that drives the motor.

In the motor drive control circuit, the rotation control amplifier, rotation limiting comparator, PWM output comparator, and motor-driver control circuit are preferably integrated on a semiconductor substrate.

A motor apparatus of another preferred embodiment of the present invention includes the above-described motor drive control circuit, a motor driver controlled by the motor drive control circuit, and a motor driven by the motor driver.

The motor drive control circuit of the first preferred embodiment of the present invention and a motor apparatus using such a circuit are provided with a rotation limiting comparator in parallel with a rotation control amplifier. Therefore, the elements defining the motor driver can be operated more in a safe operation region and unnecessary power consumption can be minimized.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The motor drive control circuit of a PWM control system of a first preferred embodiment for carrying out the present invention and a motor apparatus including such a motor drive control circuit will be explained below with reference toFIG. 1. A motor apparatus1shown inFIG. 1includes a motor2, a motor driver7for driving the motor2, and a motor drive control circuit6for controlling the motor driver7.

The motor2includes a rotor9having a permanent magnet; coils LU, LV, LWof the U phase, V phase, W phase that are Y-type connected to control the rotation of the rotor9; Hall elements HU, HV, HWfor detecting the position (phase) of the rotor9and outputting the rotation position detection signals (Hall signals); and a rotation speed counter4for detecting the rotation speed of the motor2(rotor9). The rotation position detection signals (Hall signals) of the Hall elements HU, HV, HWare differential sine waves HU+, HU−, HV+, HV−, HW+, HW−in the U phase, V phase, W phase, respectively, and the difference between the phases is 120°. The detection output of the rotation speed counter4is inputted to the motor control command unit (not shown in the figure) having a CPU, and the CPU generates a rotation speed control voltage for setting the motor2to the desired rotation speed based on the detection output, and outputs this rotation speed control voltage to the signal input terminal SIG of the motor drive control circuit6.

The motor driver7includes three output transistors TUU, TVU, TWUon the power source side and three output transistors TUL, TVL, TWLon the ground side; the transistors preferably being N-type MOS transistors. The source of the output transistor TUUon the power source side and the drain of the output transistor TULon the ground side are connected to the coil LUof the U phase of the motor2. The source of the transistor TVUon the power source side and the drain of the output transistor TVLon the ground side are connected to the coil LVof the V phase of the motor2, and the source of the transistor TWUon the power source side and the drain of the output transistor TWLon the ground side are connected to the coil LWof the W phase of the motor2. The drains of the output transistors TUU, TVU, TWUon the power source side are connected to the power source VMfor driving the motor, and the sources of the transistors TUL, TVL, TWLon the ground side are connected to the ground via a current detection resistor12, which is the below-described impedance element. PWM signal outputs of the below-described motor-driver control circuit20are inputted to the gates of those output transistors TUU, TVU, TWU, TUL, TVL, TWL. When a current flows from the coil LUof the U phase of the motor2to the coil LVof the V phase, the PWM output from the motor-driver control circuit20is received and the output transistor TUUon the power source side and the output transistor TVLon the ground side are switched ON. When a current flows from the coil LVof the V phase to the coil LWof the W phase, the output transistor TVUon the power source side and the output transistor TWLon the ground side are switched ON. When a current flows from the coil LWof the W phase to the coil LUof the U phase, the output transistor TWUon the power source side and the output transistor TULon the ground side are switched ON. The PWM output of the motor-driver control circuit20is thus received, the output transistors on the power source side and the output transistors on the ground side are thus switched, the current quantity supplied to the motor2is varied and the rotation speed of the motor2is controlled according to the variation of the ON-OFF duty ratio based on the switching operations.

The motor drive control circuit6includes a current detection element12, which is the aforementioned impedance element for converting the drive current of the motor2into a voltage; a peak hold circuit14for receiving this voltage and holding the peak voltage of the ON period of the PWM signal; a rotation control amplifier13that inputs the peak voltage, the voltage limiting reference voltage of the reference voltage source23, and the rotation speed control voltage of the signal input terminal SIG and compares the lower of the voltage limiting reference voltage and rotation speed control voltage with the peak voltage; a rotation limiting comparator24that inputs and compares a voltage of the reference voltage source25that is substantially equal to the reference voltage source23with the peak voltage; a capacitor22for oscillation prevention that is connected to the output of the rotation control amplifier13; a Hall amplifier16for inputting the rotation phase detection signals of the Hall elements HU, HV, HWand outputting the amplified signals; a synthesis circuit17that inputs the outputs of the Hall amplifier, advances each by a constant phase, amplifies according to the voltage of the rotation control amplifier13, and outputs the polarity discrimination signals UHL, VHL, WHL; a triangular wave generator19for generating and outputting a triangular wave; a PWM output comparator18for comparing the triangular wave with the polarity discrimination signals UHL, VHL, WHLand outputting PWM signals UPWM, VPWM, WPWM; and a motor-driver control circuit20for outputting a signal for controlling the motor driver7from the output signal of the rotation limiting comparator24and PWM signals UPWM, VPWM, WPWMof the PWM output comparator18.

In the current detection resistor12, a drive current flows in the ON period of the PWM signal, and no drive current flows in the OFF period of the PWM signal because each transistor of the motor driver7is switched off. In the current detection resistor12, all the drive currents flow in the ON periods of the U phase, V phase, W phase, and the currents change depending on the respective phase. In the peak hold circuit14, the peak voltage of the voltage detected by the current detection resistor12in the ON period of the PWM signal is held within the OFF period of the PWM signal, but the voltage is gradually discharged and drops with a fixed time constant.

The rotation control amplifier13has one inversion input terminal and two non-inversion input terminals. The peak voltage of the peak hold circuit14is inputted to the inversion input terminal, the voltage limiting reference voltage of the reference voltage source23and the rotation speed control voltage of the signal input terminal SIG are inputted to two non-inversion input terminals, and as described above, the lower of the voltage limiting reference voltage and rotation speed control voltage is compared with the peak voltage. The capacitor22for oscillation prevention, which is connected to the output of the rotation control amplifier13, performs phase compensation to prevent oscillations in a loop composed of the rotation control amplifier13, synthesis circuit17, PWM output comparator18, motor-driver control circuit20, motor driver7, current detection resistor12, and peak hold circuit14. The capacitance of the capacitor is, for example, 0.01 μF.

In the rotation limiting comparator24, the peak voltage of the peak hold circuit14is inputted to a non-inversion input terminal, and the voltage of the reference voltage source25that is substantially equal to the reference voltage source23is inputted to the inversion input terminal. A unique feature herein is that a capacitor with a high capacitance, such as the capacitor22connected to the output of the rotation control amplifier13, is not connected to the output of the rotation limiting comparator24, and that the output thereof is inputted directly to the motor-driver control circuit20. Thus, the output of the rotation limiting comparator24is used to remove the extra ON period of the PWM signal created by the delay caused by the capacitor22for oscillation prevention in the motor-driver control circuit20at the time of abnormality (when an overload is applied to the motor2), as described below. Therefore, the voltage of the reference voltage source25is not required to be absolutely identical to the voltage of the reference voltage source23, if the desired operation of the motor-driver control circuit20is to be achieved.

The Hall amplifier16includes a differential amplifier for the U phase that receives the rotation phase detection signals (Hall signals) HU+, HU−of the Hall element HUat the non-inversion input terminal and inversion input terminal, respectively; a differential amplifier for the V phase that receives the rotation phase detection signals HV+, HV−of the Hall element HVat the non-inversion input terminal and inversion input terminal, respectively; and a differential amplifier for the W phase that receives the rotation phase detection signals HW+, HW−of the Hall element HWat the non-inversion input terminal and inversion input terminal, respectively. Those differential amplifiers amplify the differential voltages of respective rotation position detection signals at a constant amplification ratio and output the amplified voltages.

The synthesis circuit17inputs the rotation position detection signal outputs of the differential amplifiers for the U phase, V phase, W phase of the Hall amplifier16, amplifies them according to the output voltage of the rotation control amplifier13, and outputs the polarity discrimination signals UHL, VHL, WHL. The adjustment of the amplification ratio is performed by regulating the current source of the differential amplifier (not shown in the figure) in the synthesis circuit17with the output voltage of the rotation control amplifier13. Each input signal is advanced by a fixed phase (for example, about 30°) to apply a magnetic field at a timing that makes it possible to rotate the rotor9of the motor2with the highest efficiency.

The PWM output comparator18includes a comparator for the U phase that inputs the triangular wave of the triangular wave generator19to an inversion input terminal, inputs the polarity discrimination signal UHLof the U phase of the synthesis circuit17to the non-inversion input terminal, and compares the two; a comparator for the V phase that inputs the triangular wave to an inversion input terminal, inputs the polarity discrimination signal VHLof the V phase to the non-inversion input terminal, and compares the two; and a comparator for the W phase that inputs the triangular wave to an inversion input terminal, inputs the polarity discrimination signal WHLOf the W phase to the non-inversion input terminal, and compares the two. Therefore, PWM signals UPWM, VPWM, WPWMfor which a period with a voltage that is higher than the triangular wave serves as a high-level ON period are outputted with respect to the polarity discrimination signals UHL, VHL, WHLof the respective U phase, V phase, W phase that have a phase difference of 120°.

The motor-driver control circuit20inputs the PWM signals (PWM input) (UPWM, VPWM, WPWM) of the PWM output comparator18and, as described above, outputs the PWM signals for controlling the switching of the output transistors on the power source side and output transistors on the ground side of the motor driver7. Furthermore, the motor-driver control circuit20inputs the output signal (RL) of the rotation limiting comparator24, subtracts the pulsing output period of the rotation limiting comparator24from the ON period of the PWM signal in order to remove the extra ON period of the PWM signal that is due to the delay caused by the capacitor22for oscillation prevention in the case of abnormality, as shown by the waveform inFIG. 2, and outputs the signal (PWM output). When no abnormality has occurred, the rotation limiting comparator24produces no pulsing output and, therefore, the PWM signal with unchanged ON period is outputted to the motor driver7.

The operation performed in the case where the rotation speed of the motor2is varied will be explained below. When the rotation speed of the motor2is increased, the rotation speed control voltage inputted from the CPU to the signal input terminal SIG is increased. Then, in the rotation control amplifier13, the rotation speed control voltage becomes higher than the peak voltage of the peak hold circuit14. Therefore, the output voltage thereof rises. Then, the amplitude of the polarity discrimination signals UHL, VHL, WHLoutputted from the synthesis circuit17increases, and PWM signals each having a duty ratio with a large ON period are generated in the PWM output comparator18and outputted via the motor-driver control circuit20to the motor driver7. As a result, the drive current of the motor driver7flowing to the coils LU, LV, LWof the U phase, V phase, W phase of the motor2increases and, therefore, the rotation speed of the motor2increases. This drive current is converted into a voltage by the current detection resistor12, and the peak voltage thereof is compared with the rotation speed control voltage. The loop of such operations is repeated. As a result, the peak voltage is matched with the rotation speed control voltage and stabilized.

Conversely, when the rotation speed of the motor2is decreased, the rotation speed control voltage inputted from the CPU to the signal input terminal SIG is decreased. As a result, the operation of the rotation control amplifier13, synthesis circuit17, and PWM output comparator18is inverted with respect to that performed when the rotation speed of the motor2is increased. As a result, the drive current of the motor driver7flowing to the coils LU, LV, LWof the U phase, V phase, W phase of the motor2decreases and, therefore, the rotation speed of the motor2decreases. The loop that is identical to the above-described loop is repeated and, as a result, the peak voltage is matched with the rotation speed control voltage and stabilized.

In the case of abnormality (when an overload is applied to the motor2), the rotation speed detected by the rotation speed counter4decreases. Therefore, in order to increase the rotation speed of the motor2, the CPU increases the rotation speed control voltage outputted to the signal input terminal SIG of the motor drive control circuit6. However, because the rotation speed of the motor2does not increase, this rotation speed control voltage becomes too high. When the rotation speed control voltage exceeds the voltage limiting reference voltage of the reference voltage source23in the rotation control amplifier13, this voltage limiting reference voltage, rather than the rotation speed control voltage, is compared with the peak voltage. The comparison result of the voltage limiting reference voltage with the peak voltage of the peak hold circuit14is outputted from the rotation control amplifier13and reflected in the output of the synthesis circuit17, then the output of the PWM output comparator18, and then the rotation speed of the motor2, which is the final output. Thus, when the rotation speed control voltage becomes too high, the drive current of the motor driver7flowing to the coils LU, LV, LWof the U phase, V phase, W phase of the motor2is prevented from increasing too much and the elements are prevented from being damaged.

Parallel to the operation of the rotation control amplifier13, in the rotation limiting comparator24, when the rotation speed control voltage rises too much and the peak voltage of the peak hold circuit14follows this rise and exceeds the voltage of the reference voltage source25, the output thereof is changed to a high level and inputted to the motor-driver control circuit20. On the other hand, due to the delay of the output signal of the rotation control amplifier13connected to the capacitor22for oscillation prevention, the amplitudes of the polarity discrimination signals UHL, VHL, WHLinputted to the PWM output comparator18include extra quantities and PWM signals each containing an extra ON period in the duty ratio are outputted from the PWM output comparator18to the motor-driver control circuit20. In the motor-driver control circuit20, the extra ON period of the PWM signal is removed by subtracting the output period (high-level period) of the rotation limiting comparator24from the ON period of the PWM signal, as shown by a waveform diagram inFIG. 2. Further, when the PWM signal becomes OFF, the peak voltage of the peak hold circuit14drops via the motor driver7and current detection resistor12and, therefore, the output of the rotation limiting comparator24returns to a low level.

FIG. 3shows a voltage waveform during abnormality of the motor apparatus1that is detected with the current detection resistor12. The voltage E in the figure is a voltage limiting reference voltage of the reference voltage source23. Below this voltage is a region in which the elements defining the motor driver7are not damaged, that is, the element safe operation region. The detection voltage of the current detection element12is almost below the voltage E, and a period in which the detection voltage greatly exceeds the voltage E, as the above-described period shown by points A-B of the voltage waveform inFIG. 5, is absent.

As described above, because the motor apparatus1includes a rotation limiting comparator24in parallel with the rotation control amplifier13in the motor drive control circuit6, the extra drive current caused by the delay of the output of the rotation control amplifier13can be minimized and the elements defining the motor driver7can be operated more in a safe operation region. Furthermore, the motor apparatus1can be miniaturized by integrating at least the rotation control amplifier13, rotation limiting comparator24, synthesis circuit17, PWM output comparator18, and motor-driver control circuit20of the motor drive control circuit6on a semiconductor substrate, thereby producing one semiconductor device.