JP2905856B2 - Stepping motor control circuit - Google Patents

Abstract

The control circuit (19) receives a supply voltage (Vb) provided by a battery (7), and in response to a time-base signal (S3) it sends driving voltage pulses (Vm) to a stepping motor (5), the rotor of which causes the time (6) to be displayed. The driving pulses are also applied to the control circuit (19) which comprises an adjusting circuit (20), the function of which is to compare the voltage (Vm) of these pulses with a reference voltage (Vr) and to produce, in each pulse, interruptions, the duration and number of which are determined so as to keep the mean voltage of each pulse constant in the presence of a variation of the supply voltage. Under these conditions, the motor (5) is controlled by driving pulses of constant energy, whatever the voltage (Vb) of the battery (7). <IMAGE>

Description

Description: FIELD OF THE INVENTION The present invention relates to a control circuit for a stepping motor, especially for a wristwatch, having a rotor and a coil magnetically coupled to the rotor. . More specifically,
The present invention relates to a circuit for supplying a drive pulse of a predetermined duration from a power supply to a coil, so that the average voltage and power of the drive pulse are not affected by fluctuations in the power supply voltage.

Circuits of this kind are well known because they have several advantages, especially in small watches. In small watches, the input voltage is supplied by a battery. Depending on the type of battery, the nominal voltage of the battery will vary considerably. For example, the voltage of a mercury battery is 1.35V, and the voltages of a silver battery and a lithium battery are 1.5V and 3V, respectively. In a conventional control circuit that supplies a drive pulse having an amplitude equal to the voltage of the power supply, it is of course impossible to use another type of battery in place of one type of battery unless the operation setting of the motor is changed. Therefore, since each type of battery must correspond to a specific circuit and a problem of after-service occurs, it is a great disadvantage that the voltage differs depending on the type of battery.

In contrast, in a control circuit that can supply a drive pulse having an average voltage that is independent of changes in the input voltage from the power supply, it does not matter at all that the voltage varies depending on the type of battery. The reason why the input voltage from the power supply changes is
The battery is replaced with a different type of battery, and the battery is in a discharged state. Furthermore, in the case of this type of circuit, the average voltage of the drive pulse can be set to a value significantly lower than the value of the battery voltage. In that case, it is a great advantage that the average voltage of the driving pulse can be reduced because the coil can be made of a thick transverse line, that is, a cheap and easy-to-work line, and therefore the cost of the motor can be reduced.

In order to obtain a drive pulse having a constant average voltage without dissipating power with a voltage drop resistor, the drive pulse current was interrupted, but the interruption time and the number of interruptions during the interruption were It depended on the power supply voltage.

[Conventional technology]

For example, GB-A-2054916 has a means for detecting an output voltage of a power supply and comparing the output voltage with a reference voltage, and five preset programs for interrupting the drive pulse current. A control circuit is described. The allowable change of the power supply voltage is divided into five ranges, and each range corresponds to one of the programs. The program is set up so that the average voltage is equal to the value found at the center of each range. Therefore, the average voltage is not kept constant within the given range because the adjustment is discontinuous. As a result, at the lower end of the range, the motor may not step and its torque will decrease, but at its upper end its output will not be optimal at its upper end.

A more sophisticated control circuit having the advantage of continuously adjusting the average voltage is described in European Patent Application EP 0154889. The advanced control circuit has a swept oscillator that sets the intermittent drive pulse. The duration of these interruptions is governed by changes in the output voltage of the power supply so as to keep the average voltage of the drive pulse constant. Assuming that the oscillator has made the appropriate interruptions, this circuit allows for fine tuning.

The two circuits described above maintain the average voltage applied to the terminals of the coil constant, independent of the value of the input voltage, by setting the intermittent current through the coil during the duration of the drive pulse. It has adjustment means to enable it.
This is an open loop in which the output voltage (in this case, the average voltage) is directly dominated by the input signal (ie, the output voltage from the power supply). It is well known that this type of adjustment yields good results only if the values of the circuit elements exactly match the specifications. Even if the value of a certain important element changes small, the output signal may change greatly. This is a major drawback. On the other hand, this type of circuit
Matching it to certain properties requires strict quality control during production. Then, the production cost of the circuit increases. On the other hand, since circuit elements change over time, their characteristics cannot be guaranteed for a long period of time.

[Problems to be solved by the invention]

A main object of the present invention is to supply a drive pulse having a constant average voltage to a stepping motor to obtain a control circuit which does not have the above-mentioned disadvantages.

[Means for solving the problem]

This object is achieved according to the invention by the following control circuit. That is, a control circuit used in a stepping motor for a wristwatch that has a coil magnetically coupled to a rotor and configured to be supplied with a power supply pulse from a power supply voltage supplied by an energy source comprises: A waveform shaping circuit for receiving a reference signal and supplying a signal including one control pulse of a predetermined duration when the rotor of the stepping motor has to be stepped by one step, a reference voltage source; An input terminal for receiving the control pulse;
An output terminal, and comprising an adjustment circuit for supplying a signal composed of an intermittent control pulse obtained by intermitting the control pulse to the output terminal each time the control pulse is received, wherein the intermittent control pulse A drive circuit for intermittently connecting the coil to the power supply in response to the power supply and supplying a drive pulse to the coil formed by an intermittent power supply pulse to step the rotor by one step; The adjusting circuit includes: means for determining a difference between the reference voltage and a voltage generated between the terminals of the coil by the intermittent power supply pulse; and Switch means for determining the interruption time and the number of interruptions of each control pulse as a function of the difference so that the average voltage is kept substantially constant. The advantage of the control circuit of the present invention is that the cutoff of the drive pulse is determined by the voltage at the terminal of the coil, which is based on the principle of the closed loop adjustment, and is not determined by the power supply voltage as in the related art. There is not. In other words, the circuit of the present invention automatically controls the output signal. That is, the average voltage at the terminals of the coil is automatically controlled according to the reference signal, and is very little affected by external factors such as a change in power supply voltage or a change in temperature, or a change in the value of a circuit element. As a result, the circuit of the present invention has the advantage that it is easier to fabricate than conventional circuits and is less susceptible to various disturbance factors.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

In the following description, the present invention will be described by taking a control circuit used in combination with a stepping motor for a wristwatch as an example. The reason is that the examples particularly show the advantages of the invention. The control circuit of the invention can, of course, also be used effectively in many other fields where current consumption and operational reliability are important.

For a better understanding of the present invention, reference will first be made to the prior art. FIG. 1 shows a conventional analog electronic wristwatch, in which an oscillator circuit 1 is shown. The frequency of the oscillator circuit 1 is generally 32768 Hz, and the frequency is stabilized by a reference signal supplied from the crystal unit 2. This signal is supplied to the input terminal of the frequency divider 3. The frequency divider supplies a 1 Hz time reference signal S3 to the control circuit 4. A stepping motor 5 is connected to the control circuit 4.

The stepper motor having a rotor, a coil magnetically coupled to the rotor, and two terminals coupled to the coil drives an analog time indicator 6 provided with hands. Finally, the battery 7 supplies the power necessary to operate the wristwatch in the form of the power supply voltage Vb.

The control circuit 4 has a waveform shaping circuit 8 and a driving circuit 9.
In response to the time reference signal S3 and possibly another signal S'3 generated by the divider 3, the waveform shaping circuit provides a signal S8 having the same frequency as the time reference signal S3. The signal S8 is formed by a series of control pulses P8. The control pulses are all the same in duration, typically 7.8 ms. Signals S3 and S8 are shown in FIG. The drive circuit 9 has switching means.
For simplicity, the switching means are shown in the form of contacts X. The position of its contact is in the closed position for the duration of pulse P8, the amplitude of signal S8 is zero, the pulse
As long as P8 does not exist, it is determined by the signal P8 using means not shown so as to be in the open position.

One terminal of the contact X is connected to a terminal of the battery 7, and the other terminal of the contact X is connected to a terminal of the motor 5 by a connection line 10. The other terminal of the battery and the other terminal of the motor are connected together by the ground terminal 11 of the wristwatch. The contact X 'controlled by signal S8 (opened when contact X is closed and closed for at least some of the time that contact X is open) is connected to node 10 (to ground). Terminal 11
To the connection line 10 '). In practice, contacts X and X 'are electronic switches, such as transistors or transmission gates.

The control circuit 4 operates as follows. In response to the signal S3, the waveform shaping circuit 8 generates a control pulse P8. During the duration of the control pulse P8, the contact X is closed and the contact X 'is open. While the contact X is closed, the terminal of the motor 5 is directly connected to the battery 7 and the motor receives a current pulse, and the current pulse generates a drive pulse Pm of the voltage Vm at the terminal of the coil. The rotor steps one step in response to the current pulse.
The duration and amplitude of the pulse are equal to the duration of pulse P8 and the amplitude of input voltage Vb, respectively. The end of the drive pulse is indicated by opening contact X and closing contact X '. The contact X 'attenuates the vibration of the rotor by short-circuiting the motor.

In this type of control circuit, if there is a change in the power supply voltage Vb, the duration of the drive pulse Pm is not affected, but a similar change occurs in the amplitude of the drive pulse. However, the operation of the stepping motor is very sensitive to the amplitude of the driving pulse. Therefore, assuming that another battery having a different voltage is used instead of the battery 7, the reliability of the motor will be low and the motor will not perform optimal operation even if the motor continues to operate.

To avoid this problem, instead of the control circuit 4, a second
The control circuit 14 shown is used. This control circuit 14
Is an adjustment circuit in addition to the waveform shaping circuit 8 and the driving circuit 9.
With 15.

The power supply voltage Vb and the signal S8 are supplied to the adjustment circuit 15. This adjusting circuit is a circuit of the kind described in the above-mentioned documents, and uses a voltage Vb as a reference voltage supplied by a power supply 16.
A means (not shown) for measuring the voltage Vb by comparing with Vr is provided. The power supply 16 is preferably constituted by a conventional voltage stabilizing circuit which is supplied with power from the battery 7 and supplies the voltage Vr. Even if the power supply voltage Vb changes, the value of the voltage Vr is kept constant. The adjustment circuit 15 is configured to supply the drive circuit 9 with a signal S15 composed of a series of pulses P15 obtained by providing a break in one pulse P8. The series of pulses P15 has an interruption of duration t15, as shown in FIG.

Thus, the series of pulses P15 includes several basic pulses P'15 lasting for a time t'15. That time t '
During 15, contact X is closed and contact X 'is open. Interruption time t15 and the number thereof, or is computed time interval t15 and t'15 as a function of the supply voltage Vb, the average power of the drive pulse Pm, in other words, the average voltage V ₀ which it is the power supply within certain limits It is kept almost constant irrespective of the voltage strength. In this case, the waveform of the driving pulse voltage is because it is identical to the waveform of the signal S15, for each value of Vb, t15 to equalize the average value V ₀ which is the intermittent pulse voltage to a predetermined value as t'1
It is clear that finding a value of 5 is always possible.

During the time t15, the motor 5 is short-circuited by the contact X ', so that the magnetic energy stored in the coil is not lost. As a result, the action of each basic pulse P15 of the signal S15 is prolonged, so that the contact X 'is opened and the circuit of the rotor is cut off before the current flowing through the coil is reversed. Since the rotor circuit only breaks at the end of the series of pulses P15, the result is a very high efficiency of the motor 5 associated with the control circuit 14.

As long as the adjustment circuit 15 matches the specification, the average voltage V ₀ which the drive pulse Pm is independent of the power supply voltage Vb. However, as mentioned earlier, the price of such a circuit, which is highly dependent on the price of the components, cannot be inevitably increased if the circuit has to meet strict requirements.

A control circuit 19 according to the invention which does not have these disadvantages is shown in FIG.

Therefore, a control circuit 19 similar to the control circuit 14 has the circuits 8, 9 and the adjustment circuit 20 constituting the present invention. The voltage Vb and the voltage supplied from the reference power supply 7 similar to the reference power supply 16 are supplied to the adjustment circuit 20. The adjustment circuit 20 also has an auxiliary input terminal E. The adjustment circuit 20 receives the signal S8 at its main input terminal and supplies the signal S20 to the drive circuit 9. Further, the auxiliary input terminal E is connected to the connection point 10 by a connection line 21 and receives a voltage from the coil of the motor 5. This voltage from the coil corresponds to the value of the drive pulse Pm as long as the contact X is closed.

The signal S20 has the same waveform as the signal S15 as a whole. Therefore, the signal S20 has a series of pulses P20. The duration of the series of pulses P20 is
Is the same as the duration of The series of pulses P20 has individual elementary pulses P'20, the duration t'20 of the elementary pulse P'20 being separated by an interruption of the duration t20.

Adjusting circuit 20, and the number of interruptions and down time t20, the difference between the average voltage V ₀ and the reference voltage Vr of the drive pulse Pm is determined to be almost zero. Therefore, the average voltage V _{0 of the} pulse (which is also the output signal of the control circuit 19) depends on the reference voltage Vr, and in that sense, the reference voltage Vr functions as a control value.

Dependent signals are changes in circuit component values, power supply,
It is well known that it is not very influenced by the influence of external parameters such as temperature.

Therefore, the control circuit 19 makes it possible to particularly effectively solve the problem of replacing the wristwatch battery with another battery having a different voltage. Of course, this type of circuit also has applications in a field that is completely different from the field of watchmaking, i.e. where the stepping motor must operate optimally even with large changes in external parameters.

Since the characteristics of the control circuit 19 of the present invention are essentially based on the characteristics of the adjustment circuit 20, various embodiments of the adjustment circuit will be described below.

In the first embodiment of the adjustment circuit 20 shown in FIG. The inverting input terminal of the differential amplifier 25 is connected to the input terminal E of the adjustment circuit 20 and receives the driving pulse Pm, that is, the voltage Vm at the terminal of the coil. The non-inverting input terminal of the differential amplifier 25 is connected to the power supply 16 that supplies the reference voltage Vr. Therefore, the voltage difference (Vr−
A signal S25 corresponding to the sign of Vm) is output from the differential amplifier 25. A capacitor 26 of about 1 microfarad is connected between input terminal E and ground 11. Therefore, the capacitor 26 is directly connected to the terminal of the motor 5. Finally, contact Y
Is connected between the input terminal (receiving the signal S8) and the output terminal (producing the signal S20) of the regulating circuit 20. Thus, depending on whether the contact Y is open or closed, the amplitude of the signal S20 is zero or equal to the amplitude of the signal S8. The contact Y is closed when the voltage difference (Vr-Vm) is positive and opened when the voltage difference (Vr-Vm) is negative, with the aid of means (not shown) known to those skilled in the art. Thus, it is directly controlled by the signal S25.

Under these conditions, the circuit of FIG. 4 functions as follows. Between the control pulses P8 of the signal S8 (FIG. 9), the amplitude of the signal S20 is zero and the contact X (FIG. 3) is open. Since the motor 5 is not connected to the battery 7, the amplitude of the drive pulse Pm is zero and the capacitor 26 is discharged. Then, since the voltage difference (Vr-Vm) is positive, the contact Y is closed. When the control pulse P8 contained in the signal S20 appears, the contact X is closed and the battery 7 supplies an output current pulse. This current flows through the motor 5 and the capacitor 26. The amplitude of the drive pulse having the voltage Vm supplied to the motor and the capacitor starts to increase, causing the rotor of the motor to rotate. In relation to the pulse duration of the control pulse P8, the rise of the voltage Vm is very fast and its voltage is
Above Vr, i.e., after time t'20, contact Y is immediately opened and the amplitude of signal 20 goes to zero, but pulse P8 is still present. Then contact X
Is opened to cut off the current supplied by the battery 7. From this point, the capacitor 26 supplies a current to the motor 5 and supplies a current necessary for operating the motor 5 to the motor 5. Then, the voltage between the terminals of the capacitor 26 drops. The current corresponds to the amplitude of the drive pulse Pm. After the elapse of the time t20, the amplitude of the drive pulse Pm becomes lower than the reference voltage Vr, and the contact X is closed by closing the contact Y, so that a current flows from the battery 7. Then, the amplitude of the drive pulse Pm starts to increase, and after increasing to the reference voltage Vr or more, the contact Y opens to cut off the current supplied by the battery again. Motor which receives a driving voltage pulse having an average voltage amplitude V ₀ constant equal to the reference voltage Vr is finished of it rotating, so as to perform one complete incremented, contact Y until the pulse P8 ends Open and close continuously.

During the duration of the drive pulse, the signal S20
Consists of a series of elementary pulses P'20 (of duration t'20) separated from one another by an interruption time t20. Their interruption time and duration can vary during the duration of the drive pulse. The reason is that those times depend on the motor current flowing through the motor. Motor current is a function of the instantaneous rotational speed of the rotor. Thus, the overall waveform of signal S20 is similar to the waveform of signal S15, and for that reason they are represented by the same waveform in FIG.

However, it has to be noted here that while the time t15 was a function of the input voltage Vb, the time interval t20 is not directly related to the input voltage Vb. Because of the time interval
t20 depends on only the time required for the voltage difference (Vr-Vm) to change from a negative value to a positive value.

However, the time interval t2 of the interruption so determined
0 is extremely short. This is because the change in the amplitude of the drive pulse Pm is very small and sufficient to change the sign of the voltage difference (Vr−Vm). As a result, the operating frequency of the contact Y is high. However, the contact is actually an electronic switching device, and the power consumption of the switching device increases as the operating frequency increases, so that the power consumption can be excessive.

In order to better determine the time interval t20, it is advantageous to control the contact Y with the output signal S27 of the Schmitt trigger 27. The input terminal of the Schmitt trigger is the amplifier 25
Output terminal. The amplitude of the pulse Pm is the reference voltage Vr
, The signal S25 continuously changes opposite to the amplitude of the pulse Pm. When the signal S25 increases and reaches the first level, the Schmitt trigger 27 generates an output signal in the first state, closes the contact point Y, and decreases the signal S25 to the first level.
When a second level lower than the second level is reached, a second state output signal is generated to open the contact Y. Thus, the time interval t20 corresponds to the time required for the signal S25 to change from the first level to the second level, and thus depends on the amplification of the amplifier 25 and the difference between the first and second levels. I do. Similarly, the time interval t'20 coincides with the time when the signal S25 changes from the second level to the first level. Since the durations t20 and t'20 are known, the number of interruptions of signal S20 is determined from the quotient of the duration of control pulse P8 divided by (t20 + t'20).

The adjustment circuit 20 shown in FIG. 4, the amplitude of the drive pulse Pm at the terminals of the motor 5, the duration of the control pulse P8, equal to the reference voltage Vr is substantially remains constant average value V _0, slight transient Fluctuate. Under such conditions, when the power supply voltage Vb increases, the basic pulse P'20
Is shortened, and the number of interruptions of the signal S20 increases. The reason is that the duration t20 of the interruption remains almost constant.

Although the adjustment circuit described above operates well, it requires a large-capacity capacitor 26. Since such capacitors are neither inexpensive nor very small, it is not easy to use this circuit in a wristwatch.

FIG. 5 shows a circuit that does not require a large-capacity capacitor. In this embodiment of the adjustment circuit 20, the power supply 16 is connected to the non-inverting input terminal of the differential amplifier 30, and the inverting input terminal of the differential amplifier 30 is connected to the terminal E of the adjustment circuit 20 via a resistor R. . This terminal E receives the drive pulse Pm. Also,
A capacitor C is connected between the inverting input terminal and the output terminal of the amplifier 30.
Is connected. Under these conditions, the amplifier 30
, A resistor R and a capacitor C constitute a two-input integration circuit 31. This integration circuit receives the voltages Vm and Vr and outputs a signal S30. The signal S30 depends on time t, be equivalent to.

The time constant RC is not important, but must be of the same order as the times t20 and t'20, and the capacitance of the capacitor C is about
Is appropriate. Therefore, signal S30 represents the value of the integral of the voltage difference (Vr-Vm) at any given time and is considered to be equal to signal S25, which is a function of the voltage difference (Vr-Vm).

The contact Y is provided between an input terminal and an output terminal of the adjustment circuit 20 (FIG. 5). As mentioned earlier, this contact X
Is closed directly when the integral of the voltage difference (Vr-Vm) is positive and opened when the integral is negative, and is controlled directly by the signal S30 using well-known means (not shown). Assume first that Therefore, contact Y is output signal S2
0 can be interrupted. In this case, the interruption causes the voltage difference (Vr−
The average value of Vm) is kept almost zero.

In order for the circuit of FIG. 5 to be able to operate under the same conditions at the beginning of each control pulse, the capacitor C is discharged by the switching means, indicated by contact Z, between two subsequent control pulses. It is desirable to make it. The contact Z connected to both ends of the resistor R is connected to the inverter 34.
Is controlled by a signal from The input terminal of inverter 34 receives signal S8. The control of the contact Z is opened for the duration of the pulse P8 of the signal S8, and the pulses P8
This is done by some means (not shown) so that it is closed when not present. Thereby, the integration circuit 31 is
It is possible to return to the initial state before each drive pulse. The contact Z can of course be provided at another location.
For example, if the inverting input terminal and the output terminal of the amplifier 30 are initially at the same potential, a contact Z can be provided at the terminal of the capacitor C.

The operating frequency of the contact Y in the circuit of FIG. 5 described above is very high for the same reason as described above for the circuit of FIG. To lower this frequency, it is advantageous to connect the Schmitt trigger 27 between the output terminal of the amplifier 30 and the contact Y. Another simpler solution is to connect a capacitor 35 between the two input terminals of the amplifier 30 and to connect a resistor 36 in series with the power supply 16 (No. 6).
Figure). Then, the first part of the sudden change in the voltage appearing at the inverting input terminal of the amplifier 30 is also transmitted to the other input terminals of the amplifier 30 via the capacitor 35, so that the voltage difference (Vr-Vm) for a short time Is kept substantially zero, and the appearance of the signal S30 can be delayed.

The control circuit 19 is controlled by the adjustment circuit 20 shown in FIGS.
The drive voltage pulse Vm supplied to the motor 5 has a maximum amplitude equal to the power supply voltage Vb, and its entire waveform is determined by the interruption of the time interval t20 and is equal to the waveform of the signal S20 (FIG. 9). When the voltage Vb changes, so that the average voltage V ₀ which the drive pulse Pm will remain constant, the time interval t20 and t'20
Changes. A typical waveform of the drive pulse Pm for two different input voltages Vb is shown in FIG. In this figure, the time t20 is almost constant, but the time t'20 is equal to the voltage Vb.
Indicates that it changes in the opposite direction.

The integration of the voltage difference (Vr-Vm) is performed in the same manner as in the adjustment circuits shown in FIGS. It is well known that this integration operation can be performed digitally by a logic circuit.
Therefore, it is within the capability of those skilled in the art to construct a logic circuit that can perform the same function as those two analog circuits.

An embodiment of such an adjustment circuit using digital technology is shown in FIG. An input terminal E of the adjustment circuit receiving the drive pulse Pm is connected to an input terminal of the analog-digital converter 40. This analog-to-digital converter, which also receives the signal S8 and the clock signal C1, produces a logic output representing the digital value at the time determined by the clock signal C1 and the amplitude of Pm during the duration of the control pulse P8 of the signal S8. The signal S40 is output. Signal S8 resets the analog-to-digital converter to zero during the absence of a control pulse.

The signal S40 is supplied to an input terminal of the microprocessor 41. This microprocessor 41 also receives the clock signal C1. The microprocessor 41 is combined with a RAM 42 and a ROM 43 containing a digital value of a reference voltage Vr in addition to a control command. The microprocessor 41 supplies a signal S41 for controlling the contact Y.

Signal S41 plays the same role as signal S30 or S27 in the circuit of FIG. Although operating differently, the two circuits can perform the same function. Of course, this function can of course be performed by a wired logic circuit.

[Brief description of the drawings]

1 is a block diagram of a conventional analog wristwatch, FIG. 2 is a block diagram of a control circuit of a stepping motor including a conventional control circuit, FIG. 3 is a block diagram of a control circuit including an adjustment circuit of the present invention, 4 to 7 are detailed block circuit diagrams of different embodiments of the adjustment circuit of the present invention, and FIGS. 8 to 10 are main waveform diagrams of signals generated by the circuit described in this specification. 8 ... waveform shaping circuit, 9 ... drive circuit, 14,19 ... control circuit, 20 ... adjustment circuit, 25,30 ... differential amplifier. 34 ……
Inverter, 40 …… Analog-digital converter, 41 ……
Microprocessor.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02P 8/00-8/42 G04C 3/14

Claims (6)

(57) [Claims] 1. A stepping motor for a wristwatch having a coil magnetically coupled to a rotor and adapted to be supplied with a power supply pulse from a power supply voltage supplied by an energy source. A control circuit (19), which receives a time reference signal (S3) and generates one control pulse (P8) having a predetermined duration when the rotor of the stepping motor has to be advanced by one step. A waveform shaping circuit (8) for supplying a control signal (S8) including a reference voltage source (16), an input terminal for receiving the control pulse (P8), and an output terminal; An adjusting circuit (20) for supplying a signal (S20) composed of an intermittent control pulse (P20) obtained by intermittent control to the output terminal each time the control pulse (P8) is received, Control pulse P20) The drive for intermittently connecting the coil to the power supply in response to the power supply and supplying a drive pulse (Pm) to the coil, which is formed by an intermittent power supply pulse and moves the rotor step by step. Means for determining a difference between the reference voltage (Vr) and the voltage (Vm) generated between the terminals of the coil by the intermittent power supply pulse. , 30) and the interruption time of each control pulse (P8) so that the average voltage (Vo) between the terminals of the coil of each drive pulse (Pm) is kept substantially constant even if the power supply fluctuates. And a switch means (Y) for determining the number of interruptions as a function of the difference. 2. The stepping motor control circuit according to claim 1, wherein the adjusting circuit (20) includes a capacitor (26) coupled between terminals of the coil, and a differential amplifier. , One input terminal receives the reference voltage (Vr), and the other input terminal generates a voltage (Vr) generated between the terminals of the coil by the intermittent power supply pulse.
m) and provides a signal (S25) representing the sign of the difference between the reference voltage (Vr) and the voltage between the terminals of the coil (Vm), the signal (S25) having a negative value for the difference. A differential amplifier (25) for controlling the switch means (Y) so as to interrupt the control signal (P8) during a certain period. 3. The stepping motor control circuit according to claim 2, wherein the adjustment circuit (20) is a threshold circuit (2) controlled by a signal (S25) of the differential amplifier (25).
7), a control signal (S27) is given to the switch means (Y), and the control signal is changed to a first threshold value when the signal (S25) changes in a predetermined direction at the input of the threshold circuit. When the signal reaches the first state, the signal (S25)
Changes in the opposite direction to reach the second threshold, the state becomes the second state, and when the control signal (S27) corresponding to the negative value of the difference is in the state, the control signal (P8) is interrupted. Characteristic stepping motor control circuit. 4. A control circuit for a stepping motor according to claim 3, wherein said threshold circuit is a Schmitt circuit. 5. The control circuit for a stepping motor according to claim 1, wherein said adjustment circuit is an analog integration circuit, and receives said reference voltage (Vr) at a first input terminal. An analog integrator circuit receiving a voltage (Vm) of the coil at a second input terminal and generating a signal (S30) representing the sign of the integral of the difference between these voltages during the duration of the control signal (P8) (31) The stepping motor control circuit, wherein the signal (S30) controls the switch means (Y) so as to interrupt the control signal (P8) while the difference is negative. 6. A control circuit for a stepping motor according to claim 5, wherein said adjustment circuit (20) further comprises said analog integration circuit (31).
A threshold circuit (27) controlled by the signal (S30), and a control signal (S27) is given to the switch means (Y). The control signal (S27) is supplied to the input of the threshold circuit (27). The signal (S30) changes in a predetermined direction and the first
When the threshold value is reached, the first state is established and the signal (S3
0) changes in the opposite direction and reaches the second threshold, the state becomes the second state, and when the state of the control signal (S27) corresponding to the negative integral value of the difference is reached, the control signal (P8) is interrupted. Control circuit for a stepping motor.