JP3206376B2 - Control method of load drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a load driving circuit, and more particularly to a method for controlling a load driving circuit for driving a load by using pulse width modulation control.

[0002]

2. Description of the Related Art Conventionally, when controlling a DC motor, it has been practiced to control the speed of the DC motor by pulse width modulation (hereinafter referred to as PWM) control using a drive circuit constituted by an H-bridge. Have been done.

In the PWM control, the on / off of a switching element for driving a DC motor is controlled by a PWM pulse, thereby controlling a DC motor drive current. That is, control is performed to increase the ON time of the switching element when increasing the drive current of the DC motor, and to shorten the ON time when decreasing the drive current. Such P
As a control method of the DC motor drive circuit by the WM control, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 5-38188 is conventionally known.

In the method of controlling a DC motor drive circuit disclosed in the above publication, an H-bridge type drive circuit provided with two sets of switching element pairs each including two switching elements connected diagonally to the DC motor. Is used. The motor drive current is controlled by turning on one of the switching transistors of the switching element pair selected in accordance with the driving direction of the DC motor, and performing on / off control of the other.

[0005]

In the above-described control method of the DC motor control circuit, when the switching transistor to be turned on / off transitions from the ON state to the OFF state, a counter electromotive force is applied across the terminals of the DC motor. Power is generated. In order to protect the switching transistor from such back electromotive force, a diode is arranged in parallel with the switching transistor of the H-bridge circuit. These diodes are arranged so that when a back electromotive force of the motor acts on the switching element that is turned off, a current caused by the back electromotive force can be bypassed and allowed to flow. According to such a configuration, even if a back electromotive force is generated in the motor due to the PWM control, the switching element can be effectively protected without improper voltage being applied to the switching element.

In general, when a forward current flows through a diode, a voltage drop occurs between both terminals of the diode. For this reason, in the above-mentioned conventional control circuit, power loss occurs in the diode when the current flows back through the diode. When such a power loss occurs, heat generation from the control circuit unit increases, which causes a problem that a configuration on circuit mounting such as heat radiation processing becomes complicated. further,
Since power consumption increases, when a battery is used as a power source as in an in-vehicle system, there is also a problem that the battery life is affected. The above-described conventional control method of the DC motor control circuit has such a problem associated with the power loss due to the circulation as described above.

The present invention has been made in view of the above points, and has as its object to provide a method of controlling a load drive circuit that can suppress power loss due to reflux.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an H-bridge having a first switching element pair and a second switching element pair, which are two switching elements electrically diagonally connected to a load. In the method for controlling the load drive circuit of the formula, according to a direction of energization to the load, one of the switching elements forming one of the first switching element pair or the second switching element pair One switching element is turned on,
On / off control of the other switching element that forms a pair with the one switching element that is turned on, and the load is connected to the load so as to face the one switching element that is turned on . 1 switching element
Pair or the other of the second switching element pair
One of the switching elements that make up the element pair
This is achieved by controlling the switching element in an inverted state with the other switching element.

[0009]

[Action] In the present invention, o the other switching element
When the on / off control is on , configure the other element pair
One of the switching elements is turned off. For this reason, a drive current in a predetermined direction flows through the load via one switching element and the other switching element which are turned on.

[0010] On / off control of the other switching element
When the state is changed from the on state to the off state, the drive voltage applied to the load changes from a predetermined value to zero. Therefore, back electromotive force is generated between the terminals of the load. At this time, the other
One of the switching elements constituting the element pair is transitioned from the off state to the on state. Therefore, the circulating current due to the back electromotive force of the load is reduced by one of the switches constituting the other element pair.
The flow passes through a switching element, one of the switching elements turned on, and a load.

[0011]

FIG. 1 is a circuit diagram of a DC motor driving circuit used in this embodiment. In FIG. 1, a driving transistor 1
0 and 20 are p- channel power MOSFETs (hereinafter, p F
ET), and the gates 14 and 24 are turned on by setting the gates 14 and 24 to the low level. Also,
The driving transistors 30 and 40 have an n- channel power MO
SFET (hereinafter, n referred to as FET) is, by gates 34 and 44 is set to the high level,
It turns on.

Driving transistors 10, 20, 30, 40
Are connected to a PWM signal generator 75 or a ground terminal 76 via a switch 80. The switch 80 is connected to the driving transistors 10 and 30
Are connected to a PWM signal generator 75,
And the gates 24, 44 of the driving transistors 20, 40
Is connected to the ground terminal 76, and the gates 14, 34 of the drive transistors 10, 30 are connected to the ground terminal 76, and the gates 24, 44 of the drive transistors 20, 40 are connected to the PWM signal generator. A second state of connection is formed. In this case, the driving transistors 10 and 3 simultaneously connected to the PWM signal generator or the ground terminal 76
0 and the drive transistors 20 and 40 are controlled so as to be always in different on / off states.

Drain 1 of drive transistors 10 and 20
Both 3 and 23 are connected to a power supply 50 via a V point. The power supply 50 always outputs the rated drive voltage of the DC motor 60. Also, the source 1 of the driving transistors 10 and 20
Reference numerals 5 and 25 are connected to the drains 33 and 43 of the driving transistors 30 and 40 via points A and B shown in FIG. 1, respectively. DC motor 60 is connected between points A and B.

Driving transistors 10, 20, 30, 40
Between the source and drain of the diode 12,
22, 32 and 42 are connected. In this embodiment, the diodes 12, 22, 32, and 42 are replaced by power MOS.
It is formed by a parasitic diode generated by a pn junction formed inside the FET. These diodes 12,
22, 32, 42, drive transistors 10, 20,
It is prevented that an excessive reverse voltage is applied to 30, 40. The driving transistors 10, 20, 30, 4
When an element in which such a parasitic diode is not formed such as a bipolar transistor is used as 0, a similar configuration can be realized by using an external diode as the diodes 12, 22, 32, and 42.

When the DC motor 60 is driven in the normal rotation direction by using the control circuit having such a configuration, that is, A in FIG.
The control method when the drive current flows from point to point B is
This will be described with reference to FIG. FIG. 2 shows the PWM signal output from the PWM signal generator 75 and the driving transistors 10, 20, when the DC motor 60 is driven in the forward direction.
It is a timing chart of the control signal to the gates 14, 24, 34, and 44 of 30 and 40. The drive transistors 10 and 20 are turned on and the high level (H) when the gate voltage is at the low level (L), as shown in FIGS.
And the driving transistor 30,
Reference numeral 40 denotes an ON state when the gate voltage is H, and an OFF state when the gate voltage is L.

When the DC motor 60 is driven in the forward direction, the gates 24 and 4 of the drive transistors 20 and 40 are driven.
4 is connected to the output of the PWM pulse generator 75 and sets the switch 80 so that the gates 14 and 34 of the drive transistors 10 and 30 are connected to ground. In this case, in synchronization with the PWM signal from the PWM pulse generator 75, the gate voltages of the driving transistors 10 and 20 and the driving transistors 30 and 40 are as shown in FIGS.
It changes as shown in (D) and (E).

As shown in section a of FIG. 2A, when the PWM signal is H, the driving transistor 40 is turned on, and the driving transistor 20 is turned off. At this time, the driving transistor 10 is kept on and the driving transistor 30 is kept off. As a result, the power supply 50, V point, drive transistor 10, A point,
DC motor 60, point B, drive transistor 40, point E,
An electric current flows in the path of earth, and the DC motor 60 rotates forward.

Further, as shown in section b of FIG.
When the WM signal is L, the drive transistor 40 is turned off, so that the drive voltage applied to the DC motor 60 becomes zero. Therefore, the average value of the drive current of the DC motor 60 can be controlled by changing the duty ratio of the PWM signal. Thereby, the rotation speed of DC motor 60 can be controlled.

When the PWM pulse changes from H to L, the driving transistor 40 changes from the on state to the off state,
Further, the drive transistor 20 transitions from the off state to the on state. On the other hand, the driving transistor 10 is turned on,
Further, the drive transistors 30 are held in the off state. At this time, the drive voltage applied to the DC motor 60 changes from a predetermined value to zero. For this reason, back electromotive force is generated between both terminals of the DC motor 60, and the point A has a higher potential than the point B. At this time, since the driving transistors 20 and 10 are both in the ON state as described above, a closed circuit of a forward path including the point A, the DC motor 60, the point B driving transistor 20, the point V, the driving transistor 10, and the point A is formed. .
For this reason, an annular current, that is, a circulating current, flows through the closed circuit due to the back electromotive force. In this case, a diode 22 is provided between the source and the drain of the driving transistor 20 in the forward direction with respect to the reflux. However, the forward resistance of the diode 22 is sufficiently larger than the resistance between the source and the drain when the drive transistor 20 is on. Therefore, most of the circulating current flows through between the source and the drain of the driving transistor 20, and
The current flowing through the diode 22 is small. Therefore, according to the present embodiment, it is possible to suppress the power loss caused by the circulation flowing through the diode 22. For example, if the voltage drop when a forward current flows through the diode 22 is 0.7 V and the magnitude of the circulating current is 3.5 A, the power loss of about 2.4 W can be suppressed as compared with the conventional control method. become.

When the motor 60 is driven in the reverse direction, the gates 14 and 34 of the drive transistors 10 and 30 are connected to the output of the PWM pulse generator 75, and the gates 24 and 44 of the drive transistors 20 and 40 are connected. Set switch 80 to be connected to ground. In this case, when the PWM signal transitions from H to L, the point A, the drive transistor 10,
V point, drive transistor 20, B point, DC motor 60,
A circulating current flows in the forward path at point A. The diode 12 is provided between the source and the drain of the transistor 10 in the forward direction with respect to the circulating current. However, when a circulating current is generated, the transistor 10 is turned on, so that almost no current flows through the diode 12. As a result, the diode 12
Can be suppressed.

As described above, according to the control method of the DC motor control circuit of the present embodiment, it is possible to suppress the power loss due to the circulation. Therefore, heat generation from the control circuit due to power loss can be reduced, and the heat radiation method can be simplified. Further, since an increase in power consumption can be suppressed, when a battery is used as a power supply, deterioration of battery life can be suppressed.

In the above embodiment, the DC motor 6
0 corresponds to the load described above. The DC motor 6
0 is driven in the forward direction, the driving transistor 1
0 corresponds to one of the switching elements in the ON state, the driving transistor 40 corresponds to the other switching element, and the driving transistor 20 corresponds to the third switching element.
0 is driven in the reverse direction, the driving transistor 2
0 corresponds to the one switching element in the ON state, the driving transistor 30 corresponds to the other switching element, and the driving transistor 10 corresponds to the third switching element.

In the present embodiment, when the motor 60 is driven in the normal rotation direction, the drive transistor 10 is maintained in the ON state, and the ON / OFF of the drive transistor 40 is controlled to thereby control the DC motor 60. Although the speed is controlled, the present invention is not limited to this, and the DC motor 6
The speed of 0 may be controlled. In this case, pFETs are used for the driving transistors 10 and 20, and nFETs are used for the driving transistors 30 and 40. Then, the gates 14 and 34 of the driving transistors 10 and 30 are connected to the output of the PWM pulse generator 75, and the driving transistor 2
Set switch 80 so that gates 24 and 44 of 0 and 40 are connected to ground. According to such a configuration,
When the PWM signal is H, a drive current flows through the DC motor 60. When the PWM signal transitions from H to L, the reflux is A
Point, motor 60, point B, drive transistor 40, point E,
The current flows through the path of the driving transistor 30. For this reason, the power loss in the diode 32 provided in the forward direction with respect to the circulation is suppressed. The motor 60 is driven in the reverse direction by setting the switch 80 in the reverse direction. In this case, power loss in the diode 42 is suppressed.

Alternatively, similarly to the above embodiment, the switch 80 is formed by using nFETs for the drive transistors 10 and 20 and pFETs for the drive transistors 30 and 40.
The same operation can be obtained even if the switching between the PWM signal generator 75 and the high level voltage is performed. When the motor 60 is driven in the forward direction, the gates 14 and 34 of the driving transistors 10 and 30 are connected to the PWM pulse generator 75.
The switch 80 is set such that the gates 24 and 44 of the drive transistors 20 and 40 are connected to a high level voltage. According to this configuration, the PWM
When the signal is at L, a drive current flows through the DC motor 60. P
When the WM signal transitions from L to H, the circulation flows through the forward path including the point A, the motor 60, the point B, the drive transistor 40, the point E, and the drive transistor 30. For this reason, the power loss in the diode 32 provided in the forward direction with respect to the circulation is suppressed. By setting the switch 80 in the reverse direction, the motor 60 is driven in the reverse direction. In this case, power loss in the diode 42 is suppressed.

In the above embodiment, the diodes 12, 22, 32, and 42 are provided to protect the drive transistors 10, 20, 30, and 40. However, the present invention is not limited to this. However, the diode can be omitted.

Although the control method of this embodiment is used for controlling an H-bridge circuit for driving a DC motor, the present invention is not limited to this, and the load is driven by a pulse-like drive current. Generally used for controlling an H-bridge circuit. For example, when a step motor is driven, a drive current is controlled by an H-bridge circuit. In this case, by controlling the direction of the pulsed drive current, the force acting between the teeth on the stator side and the teeth on the rotor side of the step motor can be switched between repulsive force and attractive force. According to the control method of the H-bridge circuit of the present invention, by switching between the first state and the second state, the repulsive force and the attractive force can be switched, and the power loss in the H-bridge circuit can be suppressed. can do. Therefore, the present invention can be used for controlling such an H-bridge circuit for driving a step motor, and can save power for driving the step motor.

[0027]

As described above, according to the present invention, on / off control of the other switching element is performed by PWM control. Therefore, the speed of the load can be controlled. When the other switching element transitions from the on state to the off state, one of the switching elements forming the other element pair
The switching element transitions from the off state to the on state. For this reason,
The circulating current flowing through the diode provided in parallel with one of the switching elements forming the other element pair can be suppressed. As a result, power loss in the diode can be suppressed, and therefore, heat generation and power consumption of the load control circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a control circuit of a DC motor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a timing chart of a PWM signal and a control signal to a gate of a drive transistor during forward rotation of the DC motor according to the embodiment.

[Explanation of symbols]

 10, 20, 30, 40 Driving transistor 12, 22, 32, 42 Diode 50 Power supply 60 DC motor 75 PWM signal generator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-3512 (JP, A) JP-A-4-207313 (JP, A) JP-A-2-228124 (JP, A) JP-A-5-228 38188 (JP, A) JP-A-5-268038 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03K 17/00-17/70 H02P ^7/ 04-7/34

Claims (3)

(57) [Claims] 1. A method of controlling an H-bridge type load driving circuit including a first switching element pair and a second switching element pair, which are two switching elements electrically diagonally connected to a load. In one of the first switching element pair or the second switching element pair, one of the switching elements constituting the one element pair of the first switching element pair or the second switching element pair in an on state, On / off control of the other switching element that forms a pair with the one switching element that is turned on, and the load is connected to the load so as to face the one switching element that is turned on . Switch 1
Of the switching element pair or the second switching element pair
One of the switching elements constituting the other element pair
A method for controlling a load driving circuit, wherein a switching element is controlled to be in an inverted state with respect to the other switching element. 2. The load driving circuit according to claim 1,
In the method, the signal from a single pulse width modulation generator is switched off.
The first switching element pair and the second
Supplying one of the switching element pairs
A method of controlling a load driving circuit. 3. The load driving circuit according to claim 1,
In the controlling method, the first switching element pair and the second switch
A diode in parallel with each switching element of the switching element pair.
Control method of load drive circuit characterized by connecting
Law.