JP2000116184A - Dc motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a temperature rise in a semiconductor switching element when regenerative current is passed through a DC motor by connecting diodes having small forward voltage drop which passe regenerative current from the DC motor through a shunt resistor. SOLUTION: This is a DC motor driving circuit with a shunt resistor R8 which detects the current passed through a DC motor DCM from a DC power source by the switching control of a semiconductor switching element forming an H-bridge circuit and which is connected between the positive side of a battery B and the power input side of an H-bridge circuit. Diodes SBD1, SBD2 which pass regenerative current from the motor DCM through the shunt resistor R8 are connected between the DC motor DCM and the shunt resistor R8. As a result, the current passing through the DC motor DCM from the battery B and the regenerative current from the DC motor DCM pass through the shunt resistor R8, thus it is possible to detect the current passing through the DC motor with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor drive circuit for driving a DC motor used for, for example, a transmission for an automobile, a power steering, and the like by switching control of a semiconductor switching element constituting an H-bridge circuit.

[0002]

2. Description of the Related Art Conventionally, a DC motor driving circuit for driving a DC motor used for, for example, a transmission for an automobile, a power steering, etc., employs field effect transistors FET1, FET2, FET3 and FET4 as shown in FIG. A bridge circuit is configured, and the transistors FET1,
A DC motor DCM is connected between the sources of the FET2. A power switch SW is connected to the positive electrode of the battery B serving as a power source.
A shunt resistor R8 for detecting a current supplied from the battery B to the DC motor DCM is connected between the drains of ET1 and FET2. In addition, transistor FET
3, the source of the FET 4 is connected to the negative electrode of the battery B. Transistors FET1, FET2, FET3, F
Internal diodes TD1, TD2, TD having a relatively large forward voltage drop between the source and the drain of each of ET4.
3 and TD4 are connected. Also, the transistor FE
The gates of T1, FET2, FET3, and FET4 are connected to the transistor drive circuit IC1 via the resistors R1, R2, R3, and R4.

The transistor drive circuit IC1 outputs a drive control signal to each of the transistors FET1, FET2, FET3, and FET4 based on a motor control command from the main control circuit CPU, and is used to rotate the DC motor DCM in the forward direction. Controls the transistor FET1 to be on and performs PWM control (pulse wide modulation control) of the transistor FET4. When the DC motor DCM is rotated in the reverse direction, the transistor FET2 is turned on and the transistor FET2 is turned on.
3 is subjected to PWM control. When a drive control signal is output from the transistor drive circuit IC1 to each of the transistors FET1, FET2, FET3, and FET4 based on a motor control command from the main control circuit CPU, and the DC motor DCM is driven in the forward rotation direction or the reverse rotation direction. Flows from the battery B through the shunt resistor R8,
The voltage across the shunt resistor R8 is proportional to the current flowing from the battery B to the DC motor DCM. The operational amplifier OP inputs the voltage across the shunt resistor R8 via the resistors R6 and R7, and controls the transistor Tr with the amplified signal, so that the current flowing from the battery B to the DC motor DCM with respect to the resistor R5. A detection current proportional to is supplied. As a result, the voltage at the resistor R5 is input to the main control circuit CPU as a voltage corresponding to the current flowing from the battery B to the DC motor DCM.

In the conventional DC motor driving circuit constructed as described above, when the DC motor DCM is driven in the forward rotation direction while the power switch SW is turned on, the transistor driving circuit IC1 is switched to the transistor FET1. And the transistor FET
4 is output as a control signal for PWM control. Thus, when the transistor FET4 is in the duty-on state, the current from the positive electrode of the battery B is equal to the shunt resistance R8, the transistor FET1, the DC motor DCM, and the transistor F.
ET4 flows through the path of the negative electrode of the battery B. When the duty of the transistor FET4 is turned off from this state,
Since the current from the battery B to the DC motor DCM is cut off, the regenerative current from the DC motor DCM flows through the internal diode TD2 of the transistor FET2 and the transistor FET1, and returns to the DC motor DCM. Therefore, in this case, the regenerative current from the DC motor DCM does not flow through the shunt resistor R8.

[0005] Transistors FET1, FET2, FET
3. When the DC motor DCM is driven in the reverse rotation direction after turning off all the FETs 4, the transistor drive circuit IC
From 1, a control signal for controlling the transistor FET2 to be turned on and for PWM-controlling the transistor FET3 is output. Thus, when the transistor FET3 is in the duty-on state, the current from the positive electrode of the battery B is reduced by the shunt resistor R8, the transistor FET2, and the DC motor DC.
The current flows through the path of M, the transistor FET3, and the negative electrode of the battery B. In this state, when the duty of the transistor FET3 is turned off, the current from the battery B to the DC motor DCM is cut off, so that the regenerative current from the DC motor DCM is applied to the internal diode T1 of the transistor FET1.
DC motor DCM flowing through D1 and transistor FET2
Return to Therefore, also in this case, the regenerative current from the DC motor DCM does not flow through the shunt resistor R8.

[0006]

In the above-described conventional DC motor drive circuit, the regenerative current of the DC motor DCM which is energized with the transistors FET3 and FET4 turned off does not flow through the shunt resistor R8. The current of the DC motor DCM based on the voltage at both ends cannot be detected accurately. That is, when the duty ratio of the transistors FET3 and FET4 is, for example, 50%, the current flowing through the shunt resistor R8 is
Since the current becomes 50% of the actual current of the CM, the current of the DC motor DCM cannot be accurately detected even if the current flowing through the shunt resistor R8 is detected. In addition, transistor FET
In general, the internal diode TD1 and the internal diode TD2 of the transistor FET2 have a large forward voltage drop, so that the loss is large when the regenerative current is applied and the amount of heat generated is large, so that the temperature of the transistors FET1 and FET2 becomes considerably high. There is.

In view of the above, the present invention provides a DC motor drive circuit capable of accurately detecting a current flowing in a DC motor and suppressing a rise in the temperature of a semiconductor switching element when a regenerative current is supplied to the DC motor. Is a problem to be solved.

[0008]

According to a first aspect of the present invention, a shunt resistor for detecting a current supplied from a DC power supply to a DC motor by a switching control of a semiconductor switching element constituting an H-bridge circuit has a positive pole of the DC power supply. In a DC motor drive circuit connected between the DC motor and a power input side of the H-bridge circuit, a diode having a small forward voltage drop for supplying a regenerative current from the DC motor to the shunt resistor is connected. .

According to a second aspect of the present invention, in the DC motor driving circuit of the first aspect, the diode uses a Schottky barrier diode, a high efficiency diode or a fast recovery diode.

Next, the main part of the present invention will be described with reference to FIG. As shown in FIG. 1, semiconductor switching elements (transistors FET1 to FET1) constituting an H-bridge circuit
The shunt resistor R8 for detecting the current supplied from the DC power supply (battery B) to the DC motor DCM by the switching control of the FET 4) is connected to the positive side of the battery B and the H
In a DC motor drive circuit connected between a power supply input side of a bridge circuit and a diode SB for supplying a regenerative current from the DC motor DCM to the shunt resistor R8.
D1 and SBD2 are connected to DC motor DCM and shunt resistor R8.
It is connected between. Also, the transistor FET1
FET4 has internal diodes TD1 to TD4,
Diodes SBD1 and SBD2 are internal diodes TD1
A schottky barrier diode having a forward voltage drop characteristic smaller than the forward voltage drop of 〜TD4 is used.

In the DC motor drive circuit shown in FIG.
When a control signal for controlling the transistor FET1 to be turned on and for controlling the duty of the transistor FET4 is output from the transistor driving circuit IC1, the current from the positive electrode of the battery B becomes the shunt resistor R8 and the transistor F
ET1, DC motor DCM, transistor FET4, current flows in the negative path of battery B, and DC motor DCM
Is driven in the forward rotation direction. In this state, when the transistor FET4 is controlled to be in the duty-off state, the current from the battery B to the DC motor DCM is cut off, and the regenerative current from the DC motor DCM
D2 flows through the shunt resistor R8 and the transistor FET1, and returns to the DC motor DCM. Similarly, DC motor DC
When M is driven in the reverse rotation direction, the current from the positive electrode of the battery B is equal to the shunt resistance R8, the transistor FET2,
DC motor DCM, transistor FET3, battery B
Flows through the path of the negative electrode. From this state, the transistor F
When ET3 is controlled to be duty-off, DC motor D
Since the current from the battery B to the CM is cut off,
The regenerative current from the DC motor DCM is a diode SBD1
Through the shunt resistor R8 and the transistor FET2,
Return to the DC motor DCM. Thus, the DC motor DC
DC motor DC from battery B for both forward rotation and reverse rotation of M
Since the current flowing through M and the regenerative current from the DC motor DCM flow through the shunt resistor R8, the current flowing through the DC motor can be accurately detected. DC motor D
Since the regenerative current from the CM flows through the diodes SBD1 and SBD2 having a smaller forward voltage drop than the internal diodes TD1 and TD2 having a larger forward voltage drop, the temperature rise of the transistors FET1 and FET2 can be suppressed.

[0012]

Next, an embodiment of the present invention will be described. FIG. 2 is a DC motor drive circuit diagram according to the embodiment of the present invention. As shown in FIG. 2, the field effect transistors FET1, FET2, FET3 and FET4
A bridge circuit is configured, and the transistor FET
1, a DC motor DCM is connected between the sources of the FET2. A power switch SW such as an ignition switch is connected to the positive electrode of the battery B serving as a power supply, and the power switch SW is connected to the transistors FET1 and FE.
A shunt resistor R8 is connected between the drains of T2. The sources of the transistors FET3 and FET4 are connected to the negative electrode of the battery B. Transistor FE
Internal diodes TD1, TD2, TD3, TD4 having a relatively large forward voltage drop are connected between the source and the drain of each of T1, FET2, FET3, and FET4. Also, transistors FET1, FET2, F
The gates of ET3 and FET4 are resistors R1, R2,
It is connected to the transistor drive circuit IC1 via R3 and R4.

The transistor drive circuit IC1 outputs a switching control signal to each of the transistors FET1, FET2, FET3, and FET4 based on a motor control command from the main control circuit CPU. Is the transistor FET1
Is turned on and the transistor FET4 is set to PWM.
Control (pulse wide modulation control). When the DC motor DCM is rotated in the reverse direction, the transistor FET2 is turned on and the transistor F2 is turned on.
ET3 is PWM controlled. The main control circuit CPU outputs a motor control command based on each signal when receiving a signal from various sensors or a signal from a switch, for example. Then, based on the motor control command, the transistor drive circuit IC1 sends the transistor FET
When the switching control signal is output to each of FET1, FET2, FET3, and FET4, the DC motor DCM is driven in the forward rotation direction or the reverse rotation direction. As will be described later, the DC motor DC
M and a regenerative current of the DC motor DCM are supplied. Therefore, the voltage across the shunt resistor R8 is proportional to the current of the DC motor DCM. The operational amplifier OP receives the voltage across the shunt resistor R8 via the resistors R6 and R7, amplifies the voltage, and controls the transistor Tr. And the transistor Tr
Through the resistor R5, a voltage corresponding to the current of the DC motor DCM is applied to the main control circuit C as a voltage corresponding to the current of the DC motor DCM.
Output to PU. The capacitor C1, the Zener diode ZD1, and the resistor R9 are circuits for stabilizing the voltage of the battery B to a predetermined control voltage and supplying the same to the main control circuit CPU.

As shown in FIG. 2, diodes SBD1, SB are connected between the DC motor DCM and the upstream side of the shunt resistor R8.
D2 is connected. These diodes SBD1, SB
D2 is the internal diodes TD1, TD2, TD3.
This is a Schottky barrier diode having a smaller forward voltage drop than TD4.

In the DC motor driving circuit configured as described above, when the power switch SW is turned on, the transistor driving circuit IC1 transmits the transistor F
ET1 is turned on and the transistor FET4
When a control signal for performing PWM control of
The current from the positive electrode of shunt resistor R8, transistor FET1, DC motor DCM, transistor FET4,
Since the current flows through the negative electrode path of the battery B, the DC motor DC
M is driven to rotate in the forward direction. When the duty of the transistor FET4 is turned off from this state, the DC motor D
Since the current from the battery B to the CM is cut off,
The regenerative current from the DC motor DCM is a diode SBD2
From the shunt resistor R8 and the transistor FET1,
Return to the DC motor DCM.

Next, transistors FET1, FET2,
After once controlling all FET3 and FET4 off,
When the DC motor DCM is driven in the reverse rotation direction, when a control signal for controlling the transistor FET2 to be turned on and for performing the PWM control of the transistor FET3 is output from the transistor driving circuit IC1, the current from the positive electrode of the battery B becomes the shunt resistance. R8, the transistor FET2, the DC motor DCM, the transistor FET3, and the negative electrode of the battery B flow. From this state, the transistor FE
When the duty of T3 is turned off, the current from the battery B to the DC motor DCM is cut off, so that the regenerative current from the DC motor DCM flows from the diode SBD1 through the shunt resistor R8 and the transistor FET2, and returns to the DC motor DCM.

As described above, the DC motor D
Since both the current supplied to the CM and the regenerative current from the DC motor DCM flow through the shunt resistor R8, the current of the DC motor DCM is determined by the shunt resistor R8, the operational amplifier OP, the transistor Tr, and the resistor R5.
The current is accurately detected by a current detection circuit composed of the above.

Also, most of the regenerative current from the DC motor DCM flows through the Schottky barrier diodes SBD1 and SBD2 having a small forward voltage drop, and does not flow through the internal diodes TD1 and TD2 having a relatively large forward voltage drop. The transistors FET1,
The temperature rise of the FET 2 is suppressed. Therefore, energy loss can be reduced. Note that this embodiment is merely an example, and thus the present invention is not limited to this embodiment.

[0019]

As described above, according to the first and second aspects of the present invention, the current supplied from the power supply to the DC motor and the regenerative current from the DC motor both flow through the shunt resistor. Can be accurately detected, and the temperature rise of the semiconductor switching element when the regenerative current flows can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main configuration of the present invention.

FIG. 2 is a circuit diagram according to an embodiment of the present invention.

FIG. 3 is a conventional DC motor drive circuit diagram.

[Explanation of symbols]

DCM DC motor FET1 to FET4 Field effect transistor SBD1, SBD2 Schottky barrier diode R8 Shunt resistor B Battery OP Operational amplifier Tr transistor TD1 to TD4 Internal diode of field effect transistor

Claims (2)

[Claims] 1. A shunt resistor for detecting a current supplied from a DC power supply to a DC motor by switching control of a semiconductor switching element constituting an H-bridge circuit has a shunt resistor connected between a positive side of the DC power supply and a power input side of the H-bridge circuit. A DC motor driving circuit, wherein a diode having a small forward voltage drop for supplying a regenerative current of the DC motor to the shunt resistor is connected. 2. The DC motor drive circuit according to claim 1, wherein the diode uses a Schottky barrier diode, a high efficiency diode, or a fast recovery diode.