JPH1098894A - Motor braking circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply complete braking to a high-speed motor. SOLUTION: If the rotational speed signal of a rotational speed detecting circuit 18 is compared with a threshold value set in a braking switching circuit 19 and the rotational speed signal is in an area higher than the threshold value, or a high-speed range, short braking of grounding one end of driving coils 1, 2, 3 is applied. If the rotational speed signal is lower than the threshold value, or reaches a low-speed range, a waveform shaping circuit 17 is controlled by a reversing rotation braking command signal from a driving braking circuit 20 based on switching output from the braking switching circuit 19 to switch the short braking to reversing rotation braking. It is thus possible to apply complete braking even to a high-speed motor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor braking circuit suitable for efficiently braking a motor.

[0002]

2. Description of the Related Art As a method of unipolar driving a motor having a plurality of phases of Y-connection type driving coils fixed to a stator to brake from a rotating state, the following method is exemplified. 1
As one method, there is a so-called short brake system in which one end of the non-commonly connected side of all drive coils of a plurality of phases is grounded, and braking is performed by cutting off power supply to all drive coils. As another method, the order of energizing the drive coils of the plurality of phases is changed, and in a transition period from forward rotation to reverse rotation, a back electromotive voltage having a period in which the power supply voltage or more is applied to the energized drive coil is generated. There is a so-called reverse rotation braking system in which braking is performed during this period.

As a braking measure for a motor having a relatively low rotation speed, a reverse rotation braking system is generally used. However, recently, in the motor market for rotatingly driving CDs, CD-ROMs, etc., high speed is required,
There is a movement in the semiconductor industry for manufacturing motor drivers to develop integrated circuits corresponding to high speed. Here, one problem remains in the braking of the motor that has been accelerated. In other words, when the reverse rotation braking method is used for braking the motor at high speed, the back electromotive voltage waveform of the drive coil fluctuates around the power supply VCC, so that as the motor rotates at higher speed, the amplitude of the back electromotive voltage increases. As a result, the power loss increases and the problem of heat generation cannot be ignored. Therefore, a short brake method is usually used as a braking measure for a high-speed motor.

Hereinafter, a sensorless motor drive circuit using a conventional short brake system will be described with reference to FIG. In FIG. 6, (1), (2), and (3) denote U-phase, V-phase, and W-phase drive coils, respectively, and one end is commonly connected to a Y connection. Drive coil (1) (2)
One end of the common connection (3) is connected to the power supply VCC via the collector-emitter path of the PNP-type power transistor (4). On the other hand, drive coils (1), (2) and (3)
Are NPN-type driving transistors (5) and (6), respectively.
It is grounded via the collector-emitter path of (7).

A start / stop circuit (8) generates a start command signal when a logic "1" (for example, 5 volts) is applied, and stops when a logic "0" (0 volt) is applied. A command signal is generated. (9) is a start-up logic which, when the start command signal is applied, has a phase difference of 120 degrees based on the oscillation clock generated by the oscillation circuit (10) and becomes high only for each phase difference period of 120 degrees. It generates three types of rectangular waves as levels. By the way, when the motor is driven in the forward rotation, the three types of rectangular waves that are sequentially set to the high level are the U-phase and the W-phase.
The phases are applied to the bases of the driving transistors (5), (7) and (6) via a waveform shaping circuit and a pre-driver, which will be described later, in the order of V-phase.

(11) is the waveform shaping circuit described above.
A back electromotive voltage (sine wave) generated in the drive coils (1), (2), and (3) is fed back, and the back electromotive voltage is shaped into three types of rectangular waves similar to those of the starting logic (9). still,
The waveform shaping circuit (11) includes drive coils (1) and (2)
(3) It is detected whether or not the back electromotive voltage is fed back. If the back electromotive voltage is not fed back, the operation of the starting logic (9) is continued. If the back electromotive voltage is fed back, Since the output of the start logic (9) becomes unnecessary, a signal for stopping the start logic (9) is given to the start logic (9). Reference numeral (12) denotes a pre-driver, which converts the rectangular wave of the starting logic (9) passed through the waveform shaping circuit (11) and the rectangular wave shaped by the waveform shaping circuit (11) into the driving transistors (5) and (6). And (7) amplify the signal to a level at which it can operate sufficiently.

When a stop command signal is generated from the starting logic (9), the stop command signal is applied to the pre-driver (12), and the pre-driver (12) is turned off. Thus, the driving transistors (5) and (6)
(7) turns off, the motor goes to a stop in the free-run state, and finally stops. At this time, the back electromotive force generated in the drive coils (1), (2), and (3) in the free running state of the motor is fed back to the waveform shaping circuit (11) to be shaped into a rectangular wave and output. Since (12) is powered off, there is no problem in stopping the motor. Further, since the start command signal is not supplied to the waveform shaping circuit (11), the control from the waveform shaping circuit (11) to the starting logic (9) is not performed.

(13) is a control circuit for controlling driving and braking of the motor. Specifically, the control circuit (13) outputs the reference voltage VCREF and the control voltage VC, but when driving the motor, the control circuit (13) outputs the reference voltage VCREF.
A control voltage VC that is always higher than F is output. For example, as the control voltage VC is higher than the reference voltage VCREF and its absolute value is larger, high-speed rotation is instructed, and as the absolute value is smaller, low-speed rotation is instructed. When braking the motor, the control voltage VC is set lower than the reference voltage VCREF. (14) is a comparator, to which the control voltage VC is applied to the-terminal, the reference voltage VCREF is applied to the + terminal, and the difference between the two input voltages is output. (15) is a drive braking circuit, which operates according to the output of the comparator (14). When the output of the comparator (14) is positive, braking of the motor is instructed, and the drive braking circuit (15) instructs the pre-driver (12) to drive the transistors (5) and (6).
A signal to turn on (7) all at the same time is output. As a result, one ends of the drive coils (1), (2) and (3) are all grounded. At the same time, the drive braking circuit (15) turns off the power transistor (4), and the drive coils (1) and (2)
The power supply to (3) is stopped. Therefore, the motor is brought into the short brake state and is stopped by braking.
At this time, the drive braking circuit (15) is operated by the waveform shaping circuit (1).
A signal for turning off the operation 1) is output, so that the operation of the pre-driver 112 is not hindered. On the other hand, when the output of the comparator (14) is negative, the drive braking circuit (15) outputs a signal for keeping the pre-driver (12) connected to a power supply, and simultaneously outputs a signal for turning on the power supply transistor (4). Output.

An absolute value circuit (16) detects the absolute value of the output of the comparator (14). When the control voltage VC is higher than the reference voltage VCREF, the drive current of the drive transistors (5), (6), (7) is controlled by controlling the amplitude of the pre-driver (12) according to the magnitude of the absolute value. That is, the control voltage VC becomes the reference voltage VCRE.
The drive current of the drive transistors (5), (6), and (7) becomes larger as F is higher, and high-speed rotation becomes possible. On the other hand, when the control voltage VC is lower than the reference voltage VCREF and the output of the comparator (14) becomes negative to instruct the braking of the motor, the pre-driver (12) simultaneously drives the driving transistors (5), (6) and (7). Since the signal for turning on is output, the output of the absolute value circuit (16) to the pre-driver (12) at this time is ignored.

[0010]

As described above, the motor drive circuit using the short brake system is constructed.
There are the following problems. Certainly, the short brake method is effective for braking the motor during high-speed rotation.However, in the period from when the braking is applied and the motor rotation speed is reduced to some extent to a low-speed rotation state until the motor stops, the short brake method is effective. However, if the short brake system is used continuously, the short brake system applies a brake by grounding one end of the drive coils (1), (2) and (3), so that the drive coils (1) (2) ( In 3), the back electromotive voltage is reduced and the coil current is reduced, which causes a problem that the braking effect is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a motor braking circuit that can reliably apply a brake in any rotational state of the motor.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and is characterized in that a plurality of drive coils and a plurality of drive coils are provided. In a motor drive circuit having a plurality of drive transistors driven to energize for each electrical angle, a rotation state detection circuit for detecting a rotation state of the motor, and a predetermined identification when braking the motor. In a high-speed rotation region higher than the rotation speed, braking is performed using a first braking circuit that grounds one end of all of the drive coils of the plurality of phases. And a control circuit for switching between the first and second braking circuits based on the output of the rotation state detecting circuit so as to perform braking using a second braking circuit that supplies a current in the opposite direction. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a circuit block diagram showing a motor braking circuit according to the present invention. Note that the same elements as those in the conventional circuit of FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, (17) is a waveform shaping circuit,
The difference from the waveform shaping circuit (11) of FIG. 6 lies in that a reverse rotation braking function is provided. That is, when the motor is rotated forward, the U-phase, W-phase, and V-phase drive transistors (5)
(7) A high-level rectangular wave is applied to the base of (6) in order of 120 degrees in order, and when braking is applied to the motor, the U-phase and V-phase are applied to apply a reverse rotation torque to the motor. Phase, W phase drive transistor (5) (6)
The waveform shaping circuit (17) is configured to apply a rectangular wave having a high level by 120 degrees to the base of (7) in order.
The order in which rectangular waves are applied to the driving transistors (5), (6), and (7) can be switched. Details will be described later.

A rotation speed detection circuit (18) detects the rotation speed of the motor based on the back electromotive force of the drive coils (1), (2) and (3) and outputs a rotation speed signal. . (19) is a brake switching circuit for switching between the short brake method and the reverse rotation brake method, in which a threshold value indicating a certain reference speed is set, and when the rotation speed signal is larger than the threshold value, the short brake method is selected. When the rotation speed signal is smaller than the threshold value, a selection signal for selecting the reverse rotation braking method is output. Specifically, the brake switching circuit (19) outputs a high level when the short brake system is selected, and outputs a low level when the reverse brake system is selected.

A drive braking circuit (20) is different from the drive braking circuit (15) shown in the conventional circuit of FIG. 6 in that a waveform shaping circuit (17) receives the output of the brake switching circuit (19).
In this case, a reverse braking instruction is issued. (21) is a reverse rotation prevention circuit. When the rotation speed signal of the rotation speed detection circuit (19) becomes smaller than the threshold value of the braking circuit (19), the driving braking circuit (20) reversely rotates with respect to the waveform shaping circuit (17). The brake is instructed, and a force for reverse rotation is applied to the forward rotating motor, that is, the reverse rotation torque is given, so that the motor decelerates, but if this state continues forever, the motor passes the stop state and reversely rotates. I will. In order to prevent this reverse rotation, the reverse rotation prevention circuit (21) detects the state of the back electromotive voltage of the drive coils (1), (2) and (3), and
When it is detected that a back electromotive voltage is generated in the order of U phase, V phase, and W phase with a phase difference of
7) and a signal for turning off the pre-driver (12). The energization order of the drive coils (1), (2), and (3) in the forward rotation state of the motor is W-phase, V-phase, and U-phase.

In FIG. 1, the control voltage VC generated from the control circuit (13) becomes lower than the reference voltage VCREF,
When braking of the motor is instructed, the drive braking circuit (20) attempts to perform braking of the motor by either the short brake method or the reverse rotation braking method. Requires output. For example, when the rotation speed signal obtained from the rotation speed detection circuit (18) is higher than a threshold value set in the braking switching circuit (19), a high level is output from the braking switching circuit (19), and the driving braking circuit (20) is output. ) Applies a short brake to the motor. That is, the drive braking circuit (20) provides the drive transistors (5) and (6) to the pre-driver (12).
(7) outputs a signal that is always on, outputs a signal for turning off the waveform shaping circuit (17), and also outputs a signal for turning off the power transistor (4). As a result, one ends of the drive coils (1), (2) and (3) are grounded, and braking by the short brake is started.

Thereafter, the motor is decelerated by braking by the short brake system, and the rotation speed detecting circuit (18)
When the rotation speed signal obtained in step (1) becomes lower than the threshold value set in the braking switching circuit (19), the output of the braking switching circuit (19) changes from high level to low level, and this low level output is output from the driving braking circuit ( 20). As a result, the short brake is released, that is, the waveform shaping circuit (17) is turned on and the pre-driver (12)
Is a function to amplify the output of the waveform shaping circuit (17),
The power transistor (4) turns on. Then, a command signal for reverse braking is applied from the drive braking circuit (20) to the waveform shaping circuit (17).

FIG. 2 shows a specific circuit of the waveform shaping circuit (17), and its configuration and operation will be described with reference to the waveform diagrams of FIGS. 3, 4, and 5. FIG. In FIG. 2, (22)
Is a U-phase comparator, and the power supply voltage VC is
C is applied. The + terminal has a resistance R (2
3) the back electromotive voltage of the U-phase drive coil (1) is applied, and the back electromotive voltage of the V phase drive coil (2) is connected in the forward direction to the diode (24) and the resistance 2R. A diode (2) which is applied via a resistor (25) and whose back electromotive voltage of the W-phase drive coil (3) is connected in the forward direction.
6) and a resistor (27) having a resistance value of 2R. That is, the + terminal of the U-phase comparator (22) has a back electromotive voltage waveform of the drive coil (1) and a drive coil when the diodes (24) and (26) are turned on according to the level of the back electromotive voltage waveform. (2) The back electromotive voltage waveforms of (3) are mixed and applied.

Similarly, (28) is a W-phase comparator, and the power supply voltage VCC is applied to the-terminal. Also,
A back electromotive voltage of the W-phase drive coil (3) is applied to the + terminal via a resistor (29) having a resistance value R, and a back electromotive voltage of the U-phase drive coil (1) is connected in the forward direction. A diode (32) and a resistor (2R), which are applied via a diode (30) and a resistor (31) having a resistance of 2R, and to which the back electromotive force of the V-phase drive coil (2) is connected in the forward direction. (33). That is, the + terminal of the W-phase comparator (28) has a back electromotive voltage waveform of the drive coil (3) and a drive coil when the diodes (30) and (32) are turned on according to the level of the back electromotive voltage waveform. (1)
The back electromotive voltage waveform of (2) is mixed and applied.

Similarly, (34) is a V-phase comparator, and the power supply voltage VCC is applied to the-terminal. Also,
A back electromotive voltage of the V-phase drive coil (1) is applied to the + terminal via a resistor (35) having a resistance value R, and a back electromotive voltage of the U-phase drive coil (1) is connected in the forward direction. A diode (38) and a resistor 2R having a resistance value of 2R which are applied via a diode (36) and a resistance 2R having a resistance value of 2R, and to which a back electromotive voltage of the W-phase drive coil (3) is connected in the forward direction. (39). That is, the + terminal of the V-phase comparator (34) has a back electromotive voltage waveform of the driving coil (2) and the driving coil when the diodes (36) and (38) are turned on according to the level of the back electromotive voltage waveform. (1)
The back electromotive force waveform of (3) is mixed and applied.

The back electromotive voltage of the U-phase drive coil (1) is commonly applied to one end of the resistor (23) and the anodes of the diodes (30) and (36). Similarly, the back electromotive voltage of the W-phase drive coil (3) is commonly applied to one end of the resistor (29) and the anodes of the diodes (26) and (38). Similarly, the back electromotive voltage of the V-phase drive coil (2) is commonly applied to one end of the resistor (35) and the anodes of the diodes (24) and (32).

The output of the U-phase comparator (22)
Transistors (40) (4) forming a current mirror circuit
The common emitter of 1) is connected. This common emitter is grounded via a constant current source (42). The collector of the transistor (41), which is the output of the current mirror circuit, is connected to the power supply VCC via the constant current source (43).
Further, the collector of the transistor (41) is connected to the base of an NPN transistor (44). The collector of this transistor (44) is connected to a power supply VCC via a constant current source (45), and its emitter is grounded.
The collector output of the transistor (44) becomes the U-phase input of the pre-driver (12).

Similarly, the output of the W-phase comparator (28) is connected to a transistor (4
6) The common emitter of (47) is connected. This common emitter is grounded via a constant current source (48). The collector of the transistor (47), which is the output of the current mirror circuit, is connected to the power supply VCC via the constant current source (49). Further, the collector of the transistor (47) is N
The base of the PN transistor (50) is connected.
The collector of this transistor (50) is a constant current source (5
1) is connected to the power supply VCC, and its emitter is grounded. The collector output of the transistor (50) becomes the W-phase input of the pre-driver (12).

Similarly, the output of the V-phase comparator (34) is connected to a transistor (5
2) The common emitter of (53) is connected. This common emitter is grounded via a constant current source (54). The collector of the transistor (53), which is the output of the current mirror circuit, is connected to the power supply VCC via the constant current source (55). Further, the collector of the transistor (53) is N
The base of the PN transistor (56) is connected.
The collector of this transistor (56) is a constant current source (5
7), and the emitter is grounded. The collector output of the transistor (56) becomes the V-phase input of the pre-driver (12).

Here, switch circuits (58), (59), and (60) are provided at the outputs of the U-phase, V-phase, and W-phase comparators (22), (34), and (28), respectively. In the U-phase switch circuit (58), one switching terminal a is connected to V
The other switching terminal b is connected to the collector of a diode-connected transistor (46) forming a W-phase current mirror circuit, and the other switching terminal b is connected to the collector of a diode-connected transistor (46) forming a W-phase current mirror circuit. You. In the W-phase switch circuit (60), one switching terminal a is connected to the collector of a diode-connected transistor (40) constituting a U-phase current mirror circuit, and the other switching terminal b is connected to a V-phase switching circuit. The current mirror circuit is connected to the collector of a diode-connected transistor (52). Also, the V-phase switch circuit (5
9), one of the switching terminals a is a diode-connected transistor (4) constituting a W-phase current mirror circuit.
6), and the other switching terminal b is connected to the collector of a diode-connected transistor (40) constituting a U-phase current mirror circuit.

Then, each switch circuit (58) (59)
At (60), a reverse brake signal REV is applied from the drive braking circuit (20) as a switch control signal. To rotate the motor forward, switch circuit (5
8) (59) and (60) are all connected to one of the switching terminals a and are shifted in phase by 120 degrees in the order of U-phase, W-phase, and V-phase, and become a high-level rectangular wave during this 120-degree period. Output from the shaping circuit (17).

The rectangular wave output operation of the waveform shaping circuit (17) will be described with reference to the waveform diagram of FIG. In the case of unipolar driving, it is noted that the back electromotive force of the drive coils (1), (2), and (3) changes around the power supply VCC, and the U-phase comparator (22) In a state in which the back electromotive voltage of the W phase is lower than VCC and higher than the power supply VCC, the ratio between the potential difference between the back electromotive voltage of the W phase and the power supply VCC and the potential difference of the back electromotive voltage of the power supply VCC and the U phase becomes 2: 1. At this point, the + terminal and the-terminal become equal at the power supply VCC. By detecting this state, the output of the U-phase comparator (22) becomes low level, and the transistors (40) and (41) constituting the current mirror circuit are activated. The U-phase rectangular wave rises to a high level. Upon receiving the low level output of the U-phase comparator (22), the transistors (52) and (53) constituting the current mirror circuit are turned off, and the transistor (56)
, The V-phase rectangular wave, which is the collector output, falls to a low level.

When the W-phase back electromotive voltage is higher than the power supply VCC and the W-phase back electromotive voltage is lower than the power supply VCC, the W-phase comparator (28)
When the ratio between the potential difference of the power supply VCC and the potential difference between the power supply VCC and the back electromotive voltage of the W phase becomes 2: 1, the + and-terminals become equal at the power supply VCC, and by detecting this state, the W-phase comparator (28 ) Goes low, the transistors (46) and (47) constituting the current mirror circuit are activated, and the W-phase rectangular wave rises to a high level. Upon receiving the low-level output of the W-phase comparator (28), the transistors (40) and (41) forming the current mirror circuit are turned off, and U, which is the collector output of the transistor (44), is turned off.
The phase square wave falls to a low level.

The V-phase comparator (34) operates when the U-phase counter-electromotive voltage is higher than the power supply VCC and the V-phase counter-electromotive voltage is lower than the power supply VCC.
When the ratio between the potential difference of the power supply VCC and the potential difference between the power supply VCC and the back electromotive voltage of the V phase becomes 2: 1, the + and-terminals become equal at the power supply VCC, and by detecting this state, the V-phase comparator (34) is detected. ) Goes low, the transistors (52) and (53) constituting the current mirror circuit are activated, and the V-phase rectangular wave rises to a high level. Upon receiving the low-level output of the V-phase comparator (34), the transistors (46) and (47) forming the current mirror circuit are turned off, and the collector output of the transistor (50) is W.
The phase square wave falls to a low level.

By repeating the above, the output of the waveform shaping circuit (17) has a phase difference of
A rectangular wave signal that repeats a high level in the order of U-phase, W-phase, and V-phase only for the 0-degree period is obtained, so that the motor rotates forward. VX is the drive coil (1) (2)
This is a voltage drop due to the product of the internal resistance of (3) and the current flowing through the drive coils (1), (2) and (3).

Next, when the motor is driven in the reverse direction, the switch circuits (58), (59) and (60) are connected to the other switch terminal b.
Just connect it to. Hereinafter, description will be made with reference to the waveform diagram of FIG. When the U-phase back electromotive voltage is lower than the power supply VCC and the V-phase back electromotive voltage is higher than the power supply VCC, the U-phase comparator (22) outputs the V-phase back electromotive voltage and the power supply VCC.
When the ratio between the potential difference of the power supply VCC and the potential difference between the power supply VCC and the back electromotive voltage of the U phase becomes 2: 1, the + and-terminals become equal at the power supply VCC, and by detecting this state, the U-phase comparator (22 ) Goes low, the transistors (40) and (41) constituting the current mirror circuit are activated, and the U-phase rectangular wave rises to a high level. Upon receiving the low-level output of the U-phase comparator (22), the transistors (46) and (47) constituting the current mirror circuit are turned off, and the collector output of the transistor (50) is W.
The phase square wave falls to a low level.

The V-phase comparator (34) outputs the W-phase counter-electromotive voltage and the power supply VCC when the W-phase counter-electromotive voltage is higher than the power supply VCC and the V-phase counter-electromotive voltage is lower than the power supply VCC.
When the ratio between the potential difference of the power supply and the potential difference between the power supply VCC and the back electromotive voltage of the V phase becomes 2: 1, the + and-terminals become equal at the power supply VCC, and by detecting this state, the V-phase comparator (34) ) Goes low, the transistors (52) and (53) constituting the current mirror circuit are activated, and the V-phase rectangular wave rises to a high level. Upon receiving the low-level output of the V-phase comparator (34), the transistors (40) and (41) forming the current mirror circuit are turned off, and U, which is the collector output of the transistor (44).
The phase square wave falls to a low level.

When the U-phase back electromotive voltage is higher than the power supply VCC and the W-phase back electromotive voltage is lower than the power supply VCC, the W-phase comparator (28)
When the ratio between the potential difference of the power supply VCC and the potential difference between the power supply VCC and the back electromotive voltage of the W phase becomes 2: 1, the + and-terminals become equal at the power supply VCC, and by detecting this state, the W-phase comparator (28 ) Goes low, the transistors (46) and (47) constituting the current mirror circuit are activated, and the W-phase rectangular wave rises to a high level. Upon receiving the low-level output of the W-phase comparator (28), the transistors (52) and (53) constituting the current mirror circuit are turned off, and V, which is the collector output of the transistor (56).
The phase square wave falls to a low level.

By repeating the above, the output of the waveform shaping circuit (17) has a phase difference of
A rectangular wave signal that repeats a high level in the order of U-phase, V-phase, and W-phase only for the 0-degree period, and the motor rotates in the reverse direction. Reverse rotation brake is a state in which the motor is rotating forward, reverse rotation of the motor gives reverse rotation torque,
This is a method of decelerating and braking the motor. Hereinafter, the reverse rotation braking operation will be described with reference to the waveform diagram of FIG. FIG.
In a state where the motor is rotating forward, the waveform shaping circuit (17) receives the reverse rotation brake command signal REV at a predetermined time T and starts the reverse rotation operation.

After time T, the switch circuits (58) (5)
9) (60) is from one switching terminal a to the other switching terminal b
, The U-phase, V-phase, and W-phase comparators (22), (28), (34)
Different phases are used to detect equality in CC. As a result, since the V-phase rectangular wave is normally at the high level of 120 degrees, it is continuously at the high level of 240 degrees, and thereafter the U-phase, V-phase, and W-phase are at the high level of 120 degrees each. Is shifted backward by 120 degrees. This rectangular wave is applied to the pre-driver (12),
The drive transistors (5), (6) and (7) are operated. As a result, the back electromotive voltage waveform changes as shown in FIG. 5 after time T, and the U phase,
Since the V-phase and W-phase rectangular waves are at a high level (hatched portion), a period in which a back electromotive voltage higher than the power supply VCC occurs during a high-level period of each phase is a period during which a braking operation is performed. As a result, the rotation speed of the motor decreases.

As described above, when braking the rotating motor, when the motor is rotating at a rotation speed higher than a certain threshold rotation speed, the short brake system is used.
Thereafter, when the rotation speed of the motor falls below the threshold value, the motor is switched to the reverse rotation braking system to apply braking to the motor, so that it is possible to reliably apply braking even to a high-speed motor.

[0037]

According to the present invention, when braking the motor, in a high-speed rotation range higher than a predetermined specific rotation speed, the braking is performed by grounding one end of all the driving coils of a plurality of phases. In the low-speed rotation range lower than the rotation speed, the braking method is switched according to the rotation state so that braking is performed by applying a current to the drive coil that is energized in a direction opposite to the direction of driving. However, the advantage that the braking can be surely obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a motor braking circuit according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of the waveform shaping circuit of FIG.

FIG. 3 is a waveform chart showing input / output waveforms at the time of forward rotation in the waveform shaping circuit of FIG. 1;

FIG. 4 is a waveform diagram showing input / output waveforms at the time of reverse rotation in the waveform shaping circuit of FIG. 1;

FIG. 5 is a waveform diagram showing input / output waveforms during a braking transition period in the waveform shaping circuit of FIG. 1;

FIG. 6 is a circuit block diagram showing a conventional motor braking circuit.

[Explanation of symbols]

 (1) (2) (3) Drive coil (17) Waveform shaping circuit (19) Brake switching circuit (20) Drive braking circuit

Claims (2)

[Claims] 1. A motor drive circuit comprising: a plurality of phase drive coils; and a plurality of drive transistors driven to energize the plurality of phase drive coils at predetermined electrical angles. When a braking is applied to the motor, a braking is performed using a first braking circuit that grounds one end of all drive coils of the plurality of phases in a high-speed rotation range higher than a predetermined specific rotation speed. In a low-speed rotation range lower than the specific rotation speed, based on the output of the rotation state detection circuit, braking is performed using a second braking circuit that applies a current in a direction opposite to that of the drive coil to be energized when driving is performed. And a control circuit for switching between the first and second braking circuits. 2. The motor braking circuit according to claim 1, wherein the second braking circuit is configured to apply braking by changing the order of energization of the driving coils of the plurality of phases.