JP4446752B2 - DC motor control circuit - Google Patents

Description

  The present invention relates to a circuit for controlling a DC motor, and more particularly to a control circuit for a DC motor having an output H bridge for supplying a load current to the motor.

  A conventional DC motor control circuit is shown in FIG. This control circuit includes a drive circuit 1 having an output H-bridge 11 that supplies a load current to the motor, a current detection circuit 2 that converts the load current into a voltage and supplies it as a detection voltage, and a reference voltage circuit 3 that supplies a reference voltage A comparison circuit 4 that compares the reference voltage and the detection voltage, an ON / OFF setting circuit 6 that supplies an off signal to the output H bridge 11 when the on signal and the detection voltage exceed the reference voltage for a certain period, and in the off period Attenuation setting circuit 7 for determining the ratio between the high-speed attenuation period and the low-speed attenuation period, and the output of the ON / OFF setting circuit 6 and the attenuation setting circuit 7 and the output of the attenuation mode (high speed or low speed) to the output H-bridge 11 The oscillation circuit 5 has an attenuation circuit 8 and an ON / OFF setting circuit 6 for sending an ON / OFF period.

  Here, the output H bridge 11 will be described with reference to FIG. The output H bridge 11 is a drive circuit configured by four switching elements S1, S2, S3, and S4. As shown in FIG. 3A, the switching element S1 and the switching element S4 or the switching element S2 and the switching element S3 are closed when the switching element S1 and the switching element S4 are turned on. When the switching element S2 and the switching element S3 are on, the load current flows in the direction of the arrow (2). When the detection voltage obtained by converting this current into a voltage exceeds the reference voltage, the output H bridge 11 is turned off to attenuate the current, and then turn on again after the off period ends to increase the load current. By repeating this, constant current control is performed.

  There are two ways to turn off the output H-bridge 11 and attenuate the current: high-speed attenuation and low-speed attenuation. As shown in FIG. 3A, the switching element S1 and the switching element S4 are closed, and the direction of the arrow (1) When an on-current is flowing through the switching element S1, the switching element S4 is opened, and the switching element S2 and the switching element S3 are closed. Since the potential difference is large, the current is greatly attenuated in the direction of the arrow (3) as shown in FIG. This is called fast decay. When the current is turned on in the direction of the arrow (2) in FIG. 3A, the current is attenuated in the direction of the arrow (4) in FIG.

  As shown in FIG. 3C, when the switching element S1 is opened at the time of OFF and the switching element S2 and the switching element S4 are closed, the current is attenuated in the direction of the arrow (5). Since there is a potential difference for the voltage drop of the two switches at both ends of the motor, the back electromotive force is small and the attenuation of the load current is small. This is called slow decay. When it is turned on in the direction of the arrow (2) in FIG. 3A, the current is attenuated in the direction of the arrow (6) in FIG.

  As described above, high-speed attenuation and low-speed attenuation are combined during the off period to control the amount of current attenuation. In addition, when a diode is inserted in parallel with the output switching element, high-speed attenuation is achieved by opening all the switching elements. When the switching element S1 and the switching element S4 are closed and the on-current is flowing in the direction of the arrow (1), if only the switching element S4 is closed, slow decay occurs. When the switching element S2 and the switching element S3 are closed and an on-current is flowing in the direction of the arrow (2), when only the switching element S2 is closed, slow decay occurs.

  The ON / OFF setting circuit 6 uses a signal supplied from the comparator as a trigger, and outputs an off signal and an on signal having a predetermined cycle. When the output H-bridge 11 changes from OFF to ON, a spike current is generated and the ON signal outputs a ON signal for a certain period because there is a possibility of malfunction. During this period, the output is forced ON and supplied from the comparison circuit 4 In other words, a signal output when the detected voltage reaches the reference voltage is ignored. This cycle is set by a built-in timer or external setting.

  The attenuation setting circuit 7 is set by a signal supplied from the ON / OFF setting circuit 6 and a built-in timer or external setting. An attenuation signal having a predetermined period is output by the signal.

  The operation of the control circuit is performed according to FIG. When an ON signal is output at time T1, the output H bridge 11 turns ON. At this time, since the load current does not reach the current value set by the reference voltage, the load current increases. When the on-period ends at time T2, the load current increases, and the detection voltage obtained by converting the load current into a voltage reaches the reference voltage, the comparator detects this and sends the signal to the ON / OFF setting circuit 6 Send to. The ON / OFF setting circuit 6 sends an OFF signal to the output H bridge 11 and the attenuation setting circuit 7. The output attenuation circuit 8 sends an attenuation mode signal (high-speed attenuation or low-speed attenuation) in the off time to the output H bridge 11 by the signal of the attenuation setting circuit 7. As a result, during the period from T2 to T3, the slow decay is performed until the period from fast decay T3 to T4. When the off period ends, it turns on again and the load current increases. Thus, constant current control is performed.

In addition, as an example of a conventional DC motor control circuit, there is a control circuit having the following configuration (see Patent Document 1). This control circuit can drive and switch the output H bridge and the output switch element of the output H bridge with a pulse width modulation signal, and can selectively set the charge mode, the slow decay mode, and the fast decay mode for the load by the output H bridge. PWM control circuit and output control for controlling the PWM control circuit by generating a control signal for switching to the low-speed attenuation mode when the load current drops below the first set current value in the high-speed attenuation mode for the load A logic circuit is provided.
JP 2002-204150 A

  In any of the above conventional examples, when high-speed attenuation is used when the load current is attenuated, the load current is greatly reduced, so that the current followability is good, but the load current ripple is increased. In addition, when low-speed attenuation is used, the load current attenuation is small, so the ripple is small, but the current follow-up property is deteriorated.

  Therefore, it is better to use slow decay to make the load current equal to the reference voltage. However, depending on the combination of the time constant of the motor load, the off time, and the motor power supply voltage, the current does not decay sufficiently during the off period. When turning on again, as described above, the load current is forcibly turned on during the on period and does not turn off, so that the load current may gradually increase with respect to the reference. Further, if the off period is extended to sufficiently attenuate the load current, the motor frequency may enter the audible range and generate vibration.

  In order to solve this problem, it is generally handled by combining low-speed attenuation and high-speed attenuation during the off period and performing constant current control. The optimal ratio of high-speed attenuation and low-speed attenuation is the motor time constant, power supply voltage, etc. Depending on the situation, a signal is sequentially applied from the outside to change the ratio according to the situation, or the high-speed attenuation ratio is controlled to be long so that it can be used under any conditions. However, if the latter method is used, the load current follows the reference, but the ripple amount increases, so that the noise and loss of the motor increase, and the average current decreases, resulting in a decrease in torque. Even in the former method, since the optimum damping ratio depends on the position of the rotor of the motor, it is technically very difficult to always control at the optimum ratio.

  The present invention has been made in view of the above-mentioned problems. The attenuation ratio setting is internally processed, and the load current is always attenuated at an optimum ratio by sequentially changing the output on / off cycle. Provided is a DC motor control circuit that can be implemented.

  In order to solve the above-described problems, a control circuit for a DC motor according to the present invention includes a driving unit having an output H bridge for supplying a load current to the motor, and converts the load current flowing in the motor into a voltage as a detection voltage. In a control circuit having current detection means to supply, reference voltage means for determining the magnitude of the load current, and comparison means for comparing the detection voltage with the reference voltage, the detection voltage is determined by the signal from the comparison means. Monitoring means for detecting a time when the voltage exceeds a reference voltage; and attenuation determining means for determining an attenuation ratio in the next off-cycle based on an attenuation ratio in the previous cycle and a signal of the monitoring means, and the detection voltage is A load current control method for detecting the timing at which the reference voltage is reached in three stages during the ON period, within a predetermined monitoring period that is monitored by the monitoring means after the ON period, and after the monitoring period. It is equipped with.

  The attenuation comparison means is based on the ratio in the previous off period, and in the next off period, if the point where the detected voltage reaches the reference voltage is in the on period, it sends a signal to the attenuation comparison means, Increase the rate of fast decay in the off period, maintain the rate if the decay rate is appropriate if it is within the monitoring period, and increase the rate of slow decay in the next off period when the monitoring period is exceeded A signal is output from the attenuation comparing means to the driving means.

  The monitoring means detects at what timing the detected voltage has reached the reference voltage based on three signals of an on period, a monitoring period, and an off period supplied from the oscillating means, and compares the signal with the attenuation comparison Configured to be sent to the means.

  According to the present invention, since the load current control means having the attenuation comparison circuit for increasing the ratio of the low-speed attenuation if the ratio of the high-speed attenuation is high and increasing the ratio of the high-speed attenuation if the ratio of the low-speed attenuation is high is provided. The ripple at the time of control is reduced as much as possible to approximate the reference voltage as much as possible. Since this control is performed inside the sequential circuit, it is possible to reduce the noise and loss of the DC motor and increase the torque without any external control.

  A circuit diagram of the best mode for carrying out the invention is shown in FIG. This control circuit has a drive circuit 1 having an output H-bridge 11 for supplying a load current to the motor, as in the conventional control circuit. Since the output H bridge 11 has the same configuration as that of the conventional output H bridge 11, description of the configuration and operation is omitted. The control circuit, like the conventional control circuit, converts a load current flowing in the motor into a voltage and supplies it as a detection voltage, a reference voltage circuit 3 that determines the magnitude of the load current, A comparison circuit 4 that compares the detection voltage with a reference voltage, and an ON / OFF setting circuit 6 that supplies an ON signal to the output H bridge 11 and supplies an OFF signal for a predetermined period when the detection voltage exceeds the reference voltage.

  Further, the control circuit in this embodiment is configured such that when the detection voltage exceeds the reference voltage by the oscillation circuit 5 that supplies three signals of the driving means ON period, the monitoring period, and the OFF period, and the signal of the comparison circuit 4 And the attenuation comparison circuit 7 for determining the attenuation ratio in the next off period based on the attenuation ratio in the previous period and the signal of the monitoring circuit 9. Further, the control circuit in this embodiment is configured to monitor the timing at which the detected voltage reaches the reference voltage during the on-period and after the monitoring period within the predetermined monitoring period monitored by the monitoring circuit 9 when the on-period has passed. Load current control means for detecting in stages is provided.

  Subsequently, an embodiment of the load current control means which is a feature of the present invention is shown in FIG. In this embodiment, the load current control means comprises an attenuation comparison circuit 7 and a monitoring circuit 9. The attenuation comparison circuit 7 includes an UP / DOWN counter 71, and the monitoring circuit 9 includes a falling edge circuit 91, a NAND circuit 92, and two latch circuits 93 and 94. The signal output to the falling edge circuit 91 and the NAND circuit 92 is output, the signal during the monitoring period of the oscillation circuit 5 is output to the NAND circuit 92, and the signal during the off period of the oscillation circuit 5 is used as the clear signal of the latch circuits 93 and 94. 94 is output. The output signal of the comparison circuit 4 is output to the latch circuits 93 and 94.

  The control circuit configured as described above will be described with reference to the operation waveform diagram of FIG. First, the drive circuit 1 is turned on by the ON signal, and the load current increases. When the detection voltage reaches the reference voltage after the end of the ON signal, the load voltage is turned OFF for a predetermined period. At this time, the load current is attenuated by high-speed attenuation or low-speed attenuation according to the signal supplied by the attenuation comparison circuit 7. As shown in FIG. 2, the timing at which the detected voltage reaches the reference voltage is detected in three stages after the monitoring period, within the predetermined monitoring period monitored by the monitoring circuit 9 during the ON period, during the ON period. .

  First, as shown in FIG. 2A, if it is during the ON period, it is determined that the load current is not sufficiently attenuated during the previous OFF period, and the rate of high-speed attenuation is increased with respect to the previous ratio to increase the amount of attenuation of the load current. Further, as shown in FIG. 2B, if the ratio is within the monitoring period, the previous ratio is maintained assuming that the ratio is optimal. As shown in FIG. 2C, that is, after the monitoring period and before the off period, it is determined that the previous attenuation amount is too large, the ratio of the low-speed attenuation is increased in the next period, and a signal is output from the attenuation comparison circuit 7 to the drive circuit. Reduce the attenuation of the load current.

  During the ON period, the output is forcibly turned on as in the conventional method, and the signal from the comparison circuit 4 is ignored. In FIG. 2, three types of load current waveforms are shown and have the same width for the sake of convenience, but in actuality, the load enters the off period when the load current reaches the reference and the on period ends. At this time, the monitoring period is canceled.

  Next, operations of the attenuation comparison circuit 7 and the monitoring circuit 9 shown in FIG. 4 will be described. The operation waveform diagram of each part of the monitoring circuit 9 is shown in FIG.

  One signal of an on period, a monitoring period, and an off period is input from the oscillation circuit 5. Using this signal, when the load current reaches the reference during the ON period, the output signal from the comparison circuit 4 is supplied to the latch circuit 93 by the signal D generated by the falling edge circuit 91 of the ON signal, Latched. This signal is supplied to the attenuation comparison circuit 7 as an UP clock.

  Subsequently, when the load current reaches the reference during the monitoring period, a signal in the monitoring period is supplied to the NAND circuit 92, but no signal is output from the NAND circuit 92. Therefore, no signal is output to the attenuation comparison circuit 7.

  Subsequently, when the load current reaches the reference after the monitoring period and before the off period, a signal is supplied to the latch circuit 93 by the output signal from the comparison circuit 4 and the signal E generated by the NAND circuit 92, and the latch circuit 93 Is done. This signal is supplied to the attenuation comparison circuit 7 as a DOWN clock. These signals are sent to the UP / DOWN counter 71 included in the attenuation comparison circuit 7, and the number of counters is sequentially changed to determine the attenuation ratio.

  As described above, when it is determined that the ratio of high-speed attenuation is high, the ripple amount of the load current is large. Therefore, the ratio of low-speed attenuation is increased, and when it is determined that the ratio of low-speed attenuation is high, the load current is converted to voltage. Since the obtained detection voltage may be higher than the set value by the reference voltage, the ratio of high-speed attenuation is increased and maintained if the ratio is appropriate. Control is performed so that the detected voltage obtained by converting the load current into voltage by the above method is approximated by the set value determined by the reference voltage.

  The DC motor control circuit shown in this embodiment can be integrated as an integrated circuit.

  According to the DC motor control circuit of the present invention, load current control means having an attenuation comparison circuit that increases the low-speed attenuation ratio if the high-speed attenuation ratio is high and increases the high-speed attenuation ratio if the low-speed attenuation ratio is high is provided. Therefore, the ripple during constant current control is reduced as much as possible to approximate the reference voltage as much as possible. Since this control is performed inside the sequential circuit, it is possible to reduce the noise and loss of the DC motor and increase the torque without external control.

It is a block diagram of a control circuit of a DC motor according to the present invention. 1 is an operation waveform diagram in the embodiment shown in FIG. It is a circuit diagram of the output H bridge concerning the present invention. It is the block diagram which showed the principal part of the 1st Example which concerns on this invention. 4 is a waveform diagram showing each signal in the embodiment shown in FIG. It is a block diagram of the control circuit of the conventional DC motor. FIG. 7 is an operation waveform diagram in the conventional example shown in FIG. 6.

Explanation of symbols

Reference Signs List 1 drive circuit 2 current detection circuit 3 reference voltage circuit 4 comparison circuit 5 oscillation circuit 6 ON / OFF setting circuit 7 attenuation comparison circuit (attenuation setting circuit)
8 Output attenuation circuit 9 Monitoring circuit 11 Output H bridge 71 UP / DOWN counter 91 Falling edge circuit 92 NAND circuit 93, 94 Latch circuit S1, S2, S3, S4 Switching element

Claims (2)

Driving means having an output H bridge for supplying a load current to the motor, current detecting means for converting the load current flowing in the motor into a voltage and supplying it as a detection voltage, and a reference voltage for determining the magnitude of the load current and means, in a control circuit having a comparing means for comparing said detection voltage and the reference voltage, monitoring means for detecting the time when the detected voltage by a signal of the comparing means exceeds the reference voltage, the preceding period And an attenuation comparison means for determining an attenuation ratio in the next off period based on a signal from the monitoring means, and the timing at which the detected voltage reaches the reference voltage during the on period, after the on period has passed. within a predetermined monitoring period for monitoring by the monitoring means comprises a load current control means for detecting divided into three stages after the monitoring period, the ratio the damping comparing means in the preceding off period In the next off period, if the point where the detected voltage reaches the reference voltage is in the on period, a signal is sent to the attenuation comparison means, and the fast decay ratio is increased and monitored in the next off period. If it is within the period, the attenuation ratio is determined to be appropriate and the ratio is maintained. If the monitoring period is exceeded, a signal is output from the attenuation comparison means to the drive means so that the rate of low-speed attenuation is increased in the next off period. A control circuit for a direct current motor, characterized by being configured as described above . The monitoring means detects at what timing the detected voltage has reached the reference voltage based on three signals of an on period, a monitoring period, and an off period supplied from the oscillating means, and compares the signal with the attenuation comparison 2. The DC motor control circuit according to claim 1 , wherein the DC motor control circuit is configured to be sent to the means.

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