Abstract:
A drive control signal generating circuit that generates a drive control signal for driving a motor includes an output control circuit that includes a flip-flop in which a state changes by a rotational state signal of the motor crossing a reference value and generates a motor drive control signal according to the state of the flip-flop, a clock generating circuit that generates a clock that defines a time of reading data in the flip-flop of the output control circuit; and a PWM conversion circuit that PWM-converts the drive control signal using the clock as a PWM signal. The clock has a frequency in which the output control circuit operates and has a duty ratio of the PWM signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2010-222251 filed on Sep. 30, 2010. The entire disclosure of Japanese Patent Application No. 2010-222251 filed on Sep. 30, 2010, including specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety. 
     BACKGROUND OF INVENTION 
     1. Technical Field 
     The present invention relates to a drive control signal generating circuit which generates a drive control signal for driving a motor. 
     2. Background Art 
     There exist various motors, and a type of motor in which a permanent magnet is provided on a rotor, and a phase of current supply to a plurality of coils on a side of a stator is controlled to form a rotational magnetic field and to rotate a rotor, is widely in use. 
     Supply of current to such a permanent magnet motor is generally executed by switching of a plurality of transistors. For example, an H-bridge structure is employed in which a pair of arms, in each of which two transistors are connected in series between a power supply and ground, are provided, and a coil is placed between intermediate points of the two arms. In this structure, an upper side transistor of a first arm and a lower side transistor of a second arm are switched ON so that a current of the first side is supplied to the coil, and an upper side transistor of the second arm and a lower side transistor of the first arm are switched ON so that a current of the second side is supplied to the coil. In this manner, the phase of the current flowing in the coil can be controlled. By providing the coils on different positions of the coil, providing the H-bridge at corresponding positions, and controlling the phase of the current supplied to the coil, it is possible to drive the motor. 
     Here, there is a desire to minimize the power consumption in an electronic device. In particular, the motor requires a high power at startup, but the power can be reduced after the rotation is stabilized. In order to reduce the power, PWM control is employed. However, for the PWM control, elements such as a comparator for comparing a triangular wave and a threshold value, etc., are required, and the size of the circuit is increased. 
     SUMMARY OF INVENTION 
     According to one aspect of the present invention, there is provided a drive control signal generating circuit which generates a drive control signal for driving motor, the drive control signal generating circuit comprising an output control circuit which comprises a flip-flop which reads a cross point of a reference value by a rotational state signal of the motor and which generates a motor drive control signal according to a state of the flip-flop, a clock generating circuit which generates a clock which defines a time of reading data in the flip-flop of the output control circuit, and a PWM conversion circuit which PWM-converts the drive control signal using the clock as a PWM signal, wherein the clock has a frequency at which the output control circuit operates and has a duty ratio of the PWM signal. 
     According to various aspects of the present invention, because the clock which is used as the reading signal for a flip-flop is used as the PWM signal, it becomes not necessary to provide the comparator or the like for generating the PWM signal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       A preferred embodiment of the present invention will be described in further detail based on the following drawings, wherein: 
         FIG. 1  is a block diagram showing an overall structure; 
         FIG. 2  is a diagram showing an example configuration of an output circuit; 
         FIG. 3  is a diagram showing an example of an added signal; 
         FIG. 4  is a diagram showing an example configuration of an output control circuit; 
         FIG. 5  is a diagram showing a signal waveform of each section of the output control circuit; 
         FIG. 6  is a diagram showing a structure for generating a drive control signal from a PWM signal; 
         FIG. 7  is a block diagram showing an overall structure; and 
         FIG. 8  is a diagram showing a structure of a clock generating circuit. 
     
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment of the present invention will now be described with reference to the drawings.  FIG. 1  is a diagram showing an overall structure. A system comprises a driver  100  and a motor  200 . An input signal is input to the driver  100 , and the driver  100  supplies a drive current corresponding to the input signal to the motor  200 . In this manner, rotation of the motor  200  is controlled according to the input signal. 
     The driver  100  comprises a comparator  10 , and a rotational state signal corresponding to a rotor position from a Hall element  30  provided on the motor  200  is supplied through an offset controlling circuit  32  to one terminal of the comparator  10 . More specifically, the offset controlling circuit  32  adds a predetermined offset value to the rotational state signal, and an added signal which is alternately shifted in the up-and-down direction is obtained. The added signal is supplied to the one terminal of the comparator  10 . A reference value voltage is supplied to the other terminal of the comparator  10 , and the comparator  10  detects that the added signal has reached the reference value. 
     An output of the comparator  10  is supplied to an output control circuit  12 . The output control circuit  12  determines a drive waveform (phase) of a predetermined frequency according to the output signal of the comparator  10 , and the drive control signals (OUT 1 , OUT 2 ) are controlled to be PWM-driven, so that the amplitude of the drive current is determined. The generated drive control signal is supplied to an output circuit  14 . 
     The output circuit  14  comprises a plurality of transistors, controls a current from the power supply by switching of the transistors to generate a motor drive current, and supplies the motor drive current to the motor  200 . 
       FIG. 2  shows a structure of a part of the output circuit  14  and one coil  22  of the motor  200 . As shown in  FIG. 2 , an arm comprising a series connection of two transistors Q 1  and Q 2  and an arm comprising a series connection of two transistors Q 3  and Q 4  are provided between the power supply and the ground, and a coil  22  is connected between an intermediate point of the transistors Q 1  and Q 2  and an intermediate point of the transistors Q 3  and Q 4 . By switching the transistors Q 1  and Q 4  ON and the transistors Q 2  and Q 3  OFF, a current of one direction is supplied to the coil  22 , and by switching the transistors Q 1  and Q 4  OFF and the transistors Q 2  and Q 3  ON, a current of an opposite direction is supplied to the coil  22 . The coil  22  is driven in this manner. 
     The motor  200  comprises the coil  22  and a rotor  26 . In addition, a permanent magnet is provided on the rotor  26 , and, for example, an N pole and an S pole are placed on opposed positions (positions different from each other by 180°). A stable position is determined according to a magnetic field from the coil  22 . 
     Therefore, by supplying an alternating current, it is possible to move the rotor  26  by the phase of the current and rotate the rotor  26 . In addition, by stopping the change of the phase of the current at a time of a certain phase of current, it is possible to stop the rotor at a position corresponding to the current phase at that point in time. In this manner, the rotation of the motor  200  is controlled. 
     The Hall element  30  is provided on the motor  200 , and the rotational state signal is generated according to the magnetic field from the permanent magnet of the rotor  26 . When there are one N pole and one S pole as described above, a sine wave having a period of one rotation of the rotor  26  is obtained as the rotational state signal. 
     The rotational state signal from the Hall element  30  is supplied to the offset controlling circuit  32 . The offset controlling circuit  32  shifts the rotational state signal by a predetermined amount of offset, and sets an interval between two reference cross points (in the example configuration, zero-cross points) to, for example, 150°. 
       FIG. 3  shows an example configuration in which the interval between zero-cross points is changed from 180° to 120°. The rotational state signal is a sine wave of a voltage which corresponds to 0 Gauss at 0°, to +60 Gauss at 90°, to 0 Gauss at 180°, and to −60 Gauss at 270°. Therefore, by setting the rotational state signal closer to zero by a voltage corresponding to 30 Gauss, it is possible to set the interval between two zero-cross points to 120°. Thus, when the added signal to which an amount corresponding to +30 Gauss is added on the negative (−) side (signal in which the rotational state signal is set closer to zero by an amount corresponding to 30 Gauss) reaches zero for the first time (phase of −30° of the rotational state signal), an addition of −30 Gauss (subtraction of 30 Gauss) is employed in place of +30 Gauss. In this manner, the added signal is shifted in the negative (−) direction by an amount corresponding to 60 Gauss. In the case of this example configuration, because the addition of an amount corresponding to −60 Gauss corresponds to a shift corresponding to 60°, the added signal reaches the zero from the negative (−) side for a second time at the phase of the rotational state signal of +30°. In the case of the zero for the second time, the added signal transitions to the positive (+) side with the addition of −30 Gauss unchanged. Then, at the reaching of the zero from the positive (+) side for the first time, the addition is switched to +30 Gauss. In this manner, the amount of offset is switched from +30 Gauss to −30 Gauss at the phase of the rotational state signal of 330°) (−30°, the amount of offset is switched from −30 Gauss to +30 Gauss at the phase of 150°, and these operations are repeated so that a signal of a period of 120° between the zero of the added signal for the second time to the zero for a next time is obtained. In  FIG. 3 , an example configuration where the interval between the zero-cross points is set to 120° is shown, but by adjusting the amount of offset to be added (in this case, to an amount corresponding to ±15 Gauss), a signal having a period of 150° or the like can be obtained. 
     Alternatively, a configuration may be employed in which a voltage having the same potential as a common voltage of the Hall element  30  is supplied as the reference to the other terminal of the comparator  10 . With such a configuration, the “zero” used in the Hall element  30  and the comparator  10  become equal to each other, and the electricity application period to the coil  22  can be set more accurately. 
       FIG. 4  shows an example configuration of the output control circuit  12 , which is a structure for applying 150°-electricity application (150°-electricity application generating circuit  50 ), and  FIG. 5  shows a signal waveform of each section. The output control circuit  12  operates at a frequency of a clock CLK generated by a clock generating circuit  50  to be described later. An output of the comparator (comparator raw output) detects a zero-cross point of a signal obtained by sequentially shifting the rotational state signal in a manner described above. The example configuration shows an example of 120°-electricity application, similar to  FIG. 3 . The read output when the comparator raw output is read by a flip-flop is L level for the rotational state signal of 0° to 30°, H level for the rotational state signal of 30° to 150°, L level for the rotational state signal of 150° to 180°, H level for the rotational state signal of 180° to 210°, L level for the rotational state signal of 210° to 330°, and H level for the rotational state signal of 330° to 360° ( FIG. 5(   i )). 
     The comparator raw output is supplied to a D input terminal of a flip-flop FF 1 . A predetermined clock CLK is supplied to a clock input terminal of the flip-flop FF 1 , and the flip-flop FF 1  sequentially holds the output of the comparator  10 . Because the clock CLK has a high frequency compared to the change of the output of the comparator  10 , the flip-flop FF 1  reads the output of the comparator  10  without further processing and with a delay of a predetermined period. 
     The output of the flip-flop FF 1  is supplied to a D input terminal of a flip-flop FF 2 , and the clock CLK is supplied to a clock input terminal of the flip-flop FF 2 . Therefore, the output of the flip-flop FF 2  is a signal which is delayed by one period of the clock CLK compared to the output of the flip-flop FF 1 . The output of the flip-flop FF 1  is inverted and input to an AND gate AND 1 , and the output of the flip-flop FF 2  is input to the AND gate AND 1  without being inverted. Therefore, the output of the AND gate AND 1  is a signal which rises for one period of the clock CLK when the output of the comparator  10  falls. 
     More specifically, as shown by a fall detection signal of  FIG. 5(   ii ), a signal which rises for one period of the clock CLK at the fall of the read output is obtained at the output of the AND gate AND 1 . 
     In addition, the output of the flip-flop FF 1  and an inverted output of the flip-flop FF 2  are input to an AND gate AND 2 . Therefore, as shown by a rise detection signal of  FIG. 5(   iii ), a signal which rises for one period of the clock CLK at the rise of the read output is obtained at an output of the AND gate AND 2 . 
     In  FIG. 5 , the fall detection signal (ii) and the rise detection signal (iii) are shown as pulses that are shorter than the clock CLK. This is because a signal having a higher frequency than the clock CLK is used as the clock for fall and rise detection and one clock is set as the detection pulse, but the overall operation is no different. 
     After a predetermined frequency division is applied to the clock CLK, the clock CLK is input to a continuous H/L detecting unit  40 . The continuous H/L detecting unit  40  is set to the H level, for example, when the H level at the read output continues for a period of 60° and to the L level when the L level in the read output continues for a period of 60°. Therefore, in the example configuration, the output of the continuous H/L detecting unit  40  is at the H level for a period of the rotational state signal of 90° to 270° and at the L level for the remaining half period ( FIG. 5(   iv )). 
     The output of the AND gate AND 1  is supplied to a D input terminal of a flip-flop FF 3 , and the output of the AND gate AND 2  is supplied to a D input terminal of a flip-flop FF 4 . The clock CLK is supplied to clock input terminals of the flip-flops FF 3  and FF 4 . Therefore, the outputs of the AND gates AND 1  and AND 2  are read to the flip-flops FF 3  and FF 4 . The outputs of the flip-flops FF 3  and FF 4  are input to AND gates AND 3  and AND 4 , respectively. The continuous H/L detection signal is input to the other input terminal of the AND gate AND 3 , and an inverted signal of the continuous H/L detection signal is input to the other input terminal of the AND gate AND 4 . Therefore, in the output of the AND gate AND 3 , a pulse corresponding to the rotational state signal of 0° in the fall detection signal is removed, and only pulses of 150° and 210° remain. Similarly, in the output of the AND gate AND 4 , a pulse corresponding to the rotational state signal of 180° in the rise detection signal is removed, and only pulses of 30° and 330° remain. 
     The output of the AND gate AND 3  is supplied to a set input terminal of an SR latch circuit SR 1 , and the output of the AND gate AND 4  is supplied to a reset input terminal of the SR latch circuit SR 1  ( FIG. 5(   v )). Therefore, as shown in  FIG. 5(   vi ), an offset control signal which becomes the H level at the rotational state signal of 330° and which becomes the L level at the rotational state signal of 150° is obtained at an output of the SR latch SR 1 . The output of the SR latch SR 1  is supplied to the offset controlling circuit  32 , and is used for switching control to add a predetermined offset value (corresponding to 30 Gauss) to the rotational state signal when the output is at the H level and to subtract a predetermined offset value (corresponding to 30 Gauss) from the rotational state signal when the output is at the L level. 
     The outputs of the AND gates AND 3  and AND 4  are input to an OR gate OR 1 . A double-edge signal having four pulses at 330°, 30°, 150°, and 210° is obtained at an output of the OR gate OR 1  ( FIG. 5(   vii )). The offset control signal is delayed by a predetermined amount, and then supplied to a D input terminal of a flip-flop FF 5 . The double-edge signal from the OR gate OR 1  is supplied to a clock input terminal of the flip-flop FF 5 , and a signal which becomes the H level at the rotational state signal of 30° and which becomes the L level at the rotational state signal of 210° is obtained at an output of the flip-flop FF 5  ( FIG. 5(   viii )). 
     The output of the flip-flop FF 5  is input to a NOR gate NOR 1  and an AND gate AND 5 , and the output of the SR latch SR 1  is supplied to the other input terminals of the NOR gate NOR 1  and the AND gate AND 5 . Thus, a drive control signal OUT 1  which becomes the H level only for a period from 30° to 150° is obtained at an output of the NOR gate NOR 1  ( FIG. 5(   ix )), and a drive control signal OUT 2  which becomes the H level only for a period from 210° to 330° is obtained at an output of the AND gate AND 5  ( FIG. 5(   x )). 
     The drive control signals OUT 1  and OUT 2  are supplied to the output circuit  14  to control the ON/OFF switching of the transistors Q 1  and Q 4  and the transistors Q 3  and Q 2  as in  FIG. 2 , so that the drive current control of the coil  22  as described above is executed. 
     In  FIG. 1 , because the Hall element  30  is placed at a position opposing the coil  22 , a rotational state signal which is synchronized with the coil  22  is obtained, but the position of placement of the Hall element  30  is not necessarily limited. In addition, as described above, the amount of offset to be added to or subtracted from the rotational state signal can be adjusted, to easily realize 150°-electricity application or the like. 
     The 150°-electricity application has a lower power for rotating the rotor compared to the 180°-electricity application. However, there exists an electricity application stopping period, and there may be cases where the rotation of the rotor is not started and the rotational state signal cannot be obtained. Thus, it is preferable to have the 180°-electricity application at the time of starting the operation. On the other hand, after the rotational state is stabilized, it is preferable to further reduce the power to achieve reduction of power consumption. Therefore, in the present embodiment, PWM conversion is applied to the drive control signal, to achieve reduction of power consumption. 
       FIG. 6  shows an example structure of the PWM conversion of the drive control signal. As shown, with an AND gate AND 10 , a logical product (AND) of the drive control signal OUT 1  (or OUT 2 ) and a PWM signal of a predetermined duty ratio can be determined, to obtain a PWM-converted drive control signal. For such a PWM conversion, it is necessary to generate a PWM signal of a predetermined duty ratio. Normally, the PWM signal is generated by a comparing a triangular wave of a PWM carrier frequency and a threshold voltage signal which determines a duty ratio. Therefore, for generation of the PWM signal, a circuit such as a comparator is normally required. 
     In the present embodiment, in the clock generating circuit which generates the clock CLK in  FIG. 4 , a clock of an arbitrary duty ratio is generated, and is used not only as the clock CLK, but also as the PWM signal for generating the drive control signal. 
     More specifically, as shown in  FIG. 7 , the clock which is output from the clock generating circuit  50  is supplied to the output control circuit  12  as the clock CLK, and at the same time, the clock is output as the PWM signal. 
       FIG. 8  shows a structure of the clock generating circuit  50 . A reference voltage VBGR is supplied to a positive input terminal of an operational amplifier OP 11 . The operational amplifier OP 11  has a p-channel output transistor Q 11  having a source connected to the power supply, and a drain of the output transistor Q 11  is set as an output terminal. The output terminal of the operational amplifier OP 11  is connected to ground through a resistor R 11  and is also connected to a negative input terminal. Therefore, the output terminal of the operational amplifier OP 11  is controlled by the voltage VBGR of the positive input terminal, and a current corresponding to this voltage flows to the resistor R 11  and the transistor Q 11 . 
     On a gate of the output transistor Q 11 , a gate of a p-channel transistor Q 12  having a source connected to the power supply is connected, and on a drain of the transistor Q 12 , a drain of an n-channel transistor Q 13  having a source connected to the ground is connected. Therefore, a current corresponding to the current flowing in the output transistor Q 11  flows in the transistors Q 12  and Q 13 . 
     A gate of an n-channel transistor Q 14  having a source connected to ground is connected to a gate of the transistor Q 13 . A drain of the transistor Q 14  is connected to a drain of a p-channel transistor Q 15  having a source connected to the power supply. In addition, a connection point of the transistor Q 14  and the transistor Q 15  is connected to a gate of an n-channel transistor Q 16  having a source connected to ground, and a capacitor C 11  having a second end connected to ground is connected to a gate of the transistor Q 16 . 
     When the transistor Q 15  is in the ON state, the transistor Q 14  supplies a current corresponding to the current flowing in the transistor Q 13 . On the other hand, the transistor Q 15  is set such that when the transistor Q 15  is switched ON, the transistor Q 15  supplies a current higher than the current supplied by the transistor Q 14 . Therefore, when the transistor Q 15  is switched ON, the capacitor C 11  is charged, and when the transistor Q 15  is switched OFF, the capacitor C 11  is discharged. 
     A drain of a p-channel transistor Q 17  having a source connected to the power supply is connected to a drain of the transistor Q 16 , and a connection point of the transistor Q 16  and the transistor Q 17  is connected to a set input terminal of a latch circuit L 11  through an inverter INV 11 . 
     Therefore, when the transistor Q 15  is in the ON state, the capacitor C 11  is charged, and when the charged voltage of the capacitor C 11  exceeds the threshold voltage of the transistor Q 16 , the transistor Q 16  is switched ON. On the other hand, when the transistor Q 15  is in the OFF state, the capacitor C 11  is discharged by a current flowing in the transistor  14 , and when the charged voltage of the capacitor C 11  becomes lower than the threshold voltage of the transistor Q 16 , the transistor Q 16  is switched OFF. 
     The gate of the transistor Q 13  is also connected to a gate of an n-channel transistor Q 18  having a source connected to ground. A drain of the transistor Q 18  is connected to a drain of a p-channel transistor Q 19  having a source connected to the power supply, and a connection point of the transistor Q 18  and the transistor Q 19  is connected to a gate of an n-channel transistor Q 20  having a source connected to ground, and a capacitor C 12  having a second end connected to ground is connected to a gate of the transistor Q 20 . 
     The transistor Q 19  is set such that the transistor Q 19  supplies a current higher than the transistor Q 18  when the transistor Q 19  is switched ON. Thus, when the transistor Q 19  is switched ON, the capacitor C 12  is charged, and when the transistor Q 19  is switched OFF, the capacitor C 12  is discharged. 
     A drain of a p-channel transistor Q 21  having a source connected to the power supply is connected to a drain of the transistor Q 20 , and a connection point of the transistor Q 20  and the transistor Q 21  is input to a reset input terminal of the latch circuit L 11  through an inverter INV 12 . 
     Therefore, when the transistor Q 19  is switched ON, the capacitor C 12  is charged, and when the charged voltage of the capacitor C 12  exceeds the threshold voltage of the transistor Q 20 , the transistor Q 20  is switched ON. When the transistor Q 19  is switched OFF, the capacitor C 12  is discharged by the current flowing in the transistor Q 18 , and when the charged voltage of the capacitor C 12  becomes less than the threshold voltage of the transistor Q 20 , the transistor Q 20  is switched OFF. 
     The connection point of the transistor Q 17  and the transistor Q 16  is connected to the reset input of the latch circuit L 11  through the inverter INV 11 , and the connection point of the transistor Q 19  and the transistor Q 18  is connected to the set input of the latch circuit L 11  through the inverter INV 12 . 
     The latch circuit L 11  comprises a circuit in which two NAND gates are crosswise connected, and the output is set to the H level by a set input and the output is set to the L level by a reset input of H level. More specifically, the latch circuit L 11  comprises two NAND gates NAND 11  and NAND 12 , an output of the NAND gate NAND 11  is input to the NAND gate NAND 12 , and an output of the NAND gate NAND 12  is input to the NAND gate NAND 11 . An output of the inverter INV 11  is input to the NAND gate NAND 11 , an output of the inverter INV 12  is input to the NAND gate NAND 12 , and an output of the NAND gate NAND 11  is set as the output of the latch circuit L 11 . Therefore, with a rise of the output of the inverter INV 11 , the L level is latched in the latch circuit L 11 , and with a rise of the inverter INV 12 , the H level is latched in the latch circuit L 11 . 
     The output of the latch circuit L 11  is output as a clock through two inverters INV 13  and INV 14 . 
     An output of the inverter INV 13  is supplied to the gate of the transistor Q 19 , and an output of the inverter INV 14  is supplied to the gate of the transistor Q 15 . Therefore, when the clock becomes the H level, the transistor Q 15  is switched ON and the capacitor C 11  is charged, and after a predetermined time has elapsed and the transistor Q 16  is switched ON, the latch L 11  is reset, and the output is set to the L level. When the clock is set to the L level, the transistor Q 19  is switched ON and the capacitor C 12  is charged, and after a predetermined time has elapsed and the transistor Q 20  is switched ON, the latch L 11  is set, and the output is set to the L level. These processes are repeated. 
     The frequency of the clock is determined by the capacitances of the capacitors C 11  and C 12  and sizes of the charging currents to the capacitors C 11  and C 12 . In addition, the charging currents to the capacitors C 11  and C 12  are identical to each other, and a duty ratio of the clock is set by a capacitance ratio between the capacitors C 11  and C 12 . 
     In the present embodiment, the capacitance ratio of the capacitor C 11  and the capacitor C 12  is set to 11:4. Therefore, the time when the capacitor C 11  is charged is longer, and a clock having a duty ratio of about 70% and having a longer L level period than the H level period is obtained. 
     Therefore, this clock can be used as the PWM signal. In particular, in the circuit of  FIG. 4 , only the timing of rise of the clock CLK is used. Therefore, so long as the rise can be detected, the duty ratio may be an arbitrary ratio such as 99% or 1%. Therefore, by generating the clock having a duty ratio necessary as the PWM signal at the clock generating circuit of  FIG. 6 , it is possible to not separately generate the PWM signal. Alternatively, the circuit of  FIG. 4  may be formed in a structure such that the circuit operates using only the timing of fall of the clock CLK. 
     Because the duty ratio of the PWM signal depends on the capacitance ratio of the capacitors C 11  and C 12 , it is possible to employ a variable capacitor for one or both of the capacitors C 11  and C 12 , to arbitrarily control the duty ratio of the PWM signal. In addition, the charging periods of the capacitors C 11  and C 12  can be controlled by controlling the charging currents. Therefore, it is possible to change the amount of current by employing different sizes for the transistors Q 15  and Q 19 . Moreover, it is also possible to provide a plurality of transistors and control ON/OFF switching of the plurality of transistors, to control the charging currents. 
     In the above description, the output clock of the clock generating circuit  50  is used in the output control circuit  12  which generates the 150°-electricity application signal, but the circuit which uses the clock is not limited to such a circuit. For example, the output of the flip-flop FF 1  in  FIG. 4  has a rectangular wave shape of 180°, and the drive control signals OUT 1  and OUT 2  may be generated by this signal and an inverted signal of this signal. Therefore, the output control circuit  12  may be formed as a circuit having one flip-flop, and the clock generating circuit  50  of  FIG. 8  may be used as a circuit for generating the clock for the flip-flop.