JPH1123618A - Coil drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coil drive circuit having a current detecting section where a circulation current due to the counter electromotive force can be detected surely during power interruption, as well as the conduction current to a coil, through an inexpensive arrangement. SOLUTION: The coil drive circuit comprises two pairs of switching transistors 1A, 1B and 1C, 1D connected across a driving power supply 2. The series circuits of switching transistors 1A, 1B and 1C, 1D are connected in parallel and each switching transistor includes a diode 11-14. A coil 3 is connected between the joints of respective sets of switching transistors 1A, 1B and 1C, 1D and the switching transistors 1C, 1D are connected, respectively, with current detecting resistors 4, 5. Terminal voltage 4a of the high potential side current detecting resistor 4 is taken out while being converted into a low potential side voltage through a level shifter circuit 61.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil driving circuit for driving a motor coil, an electromagnetic coil, and the like, and more particularly, to an improvement in a coil current detecting unit.

[0002]

2. Description of the Related Art For example, an H-bridge type coil drive circuit is frequently used for forward / reverse PWM control of a single-phase DC motor or the like, and FIG. 3 shows an example thereof. In the figure, two pairs of switching transistors (hereinafter simply referred to as transistors) 7A, 7B and 7C, 7D are respectively connected in series and provided to a drive power supply 2. Diodes 71, 72, 73, 74 are connected in parallel to the transistors 7A to 7D, respectively, and a motor coil 3 is connected so as to connect the connection points of the transistors 7A to 7D of each set, thereby forming an H bridge type coil. It is a drive circuit. By the way, in order to perform the current feedback control, it is necessary to detect the current flowing through the motor coil 3. Conventionally, as shown in FIG. The voltage between both ends proportional to the voltage is taken out via the insulating amplifier 91. However, in this configuration, since the high voltage of the drive power supply 2 is applied to each terminal of the current detection resistor 8, there is a problem that it is necessary to use the large and expensive insulating amplifier 91 as described above.

To solve this problem, for example, Japanese Unexamined Patent Publication (Kokai) No. 61-135390 discloses, as shown in FIG. 4, a pair of transistors 7B and 7D and a low potential side power supply line L.
It has been proposed to provide current detection resistors 81 and 82 between the two. According to this configuration, the terminal voltages of the current detection resistors 81 and 82 are suppressed to be lower than that of the low-potential-side power supply line L2. It can be taken out using a simple operational amplifier 92.

[0004]

However, in the circuit configuration proposed in the above-mentioned publication, when the transistor 7B or 7D is shut off by the PWM control, the diode 71 or 73 and the conduction from the motor coil 3 are conducted by the back electromotive force. There is a problem that the circulating current flowing through the transistor 7A or 7C cannot be detected.

Therefore, the present invention solves such a problem, and uses an inexpensive configuration without using an expensive insulating amplifier, and not only a current flowing through a coil but also a circulating current due to a coil back electromotive force. It is an object of the present invention to provide a coil drive circuit having a current detection unit that can reliably detect a current.

[0006]

In order to achieve the above object, according to the present invention, one end of a coil (3) is alternatively connected to a high-potential power line (L1) and a low-potential power line (L2). High-side switching elements (1A, 1C, 1E) and low-potential side switching elements (1B, 1D, 1F) for supplying forward and reverse current to the coil (3), and these switching elements (1A, 1B, 1C, 1D, 1E, 1F) and the diode elements (11, 12,.
13, 14, 15, 16), a current is serially connected to at least one of the high-potential side switching elements (1C, 1E) and at least one of the low-potential side switching elements (1D, 1F). The detection resistors (4, 5) are provided, and the terminal voltage of the current detection resistor (4) located on the high potential side is taken out via the level shifter circuit (61). Here, "coil" means
It broadly includes not only motor coils but also driving coils such as electromagnetic coils.

In the present invention, when a forward or reverse current is supplied to the coil (3), the forward or reverse current always passes through one of the current detection resistors (4, 5). The amount of current can be detected from the terminal voltages (4a, 5a) of the current detection resistors (4, 5) that change according to the magnitude of the current. When any of the switching elements (1B, 1D, 1E, 1F) is turned off,
By the back electromotive force of the coil (3), the high potential side switching element (1A) or (1C) and the diode (11) or (13), or the diode (15) or (16) are turned on to generate a high potential. A circulating current flows in the forward or reverse direction through the current detection resistor (4) on the side. Therefore, the amount of circulating current can be detected from the terminal voltage of the current detection resistor (4) on the high potential side. And
In the present invention, the terminal voltage (4a) of the high-potential-side current detection resistor (4) is converted to the low-potential side by the level shifter circuit (61) and taken out, so that it is not necessary to use a large and expensive insulating amplifier. .

A pair of switching elements (1A, 1B) (1C, 1D) having diodes (11 to 14) connected in series with each other and connected in parallel to each other are provided in two pairs between driving power sources (2). In the H-bridge type coil drive circuit in which the coil (3) is connected between the connection points of the switching elements (1A, 1B) (1C, 1D) of each set, the switching elements (1C, 1C, 1D)
Are respectively connected in series with current detection resistors (4, 5), and the terminal voltage (4) of the current detection resistor (4) located on the high potential side is set.
a) may be extracted via a level shifter circuit (61).

In the H-bridge type coil drive circuit, the other pair of the high-potential side switching elements (1A, 1C) and the low-potential side switching elements (1B, 1D) are electrically connected to each other so that the coil (3) has a positive direction. Supplies a reverse current. In this case, since the forward and reverse currents always pass through any of the current detection resistors (4, 5), the terminal voltages (4, 5) of the current detection resistors (4, 5) change according to the magnitude of the current flow. 4a, 5a), the amount of current flowing can be detected. On the other hand, if the low-potential-side switching elements (1B, 1D) are turned off during PWM control, the high-potential-side switching element (1A) or (1C), which is turned on, is generated by the back electromotive force of the coil (3). And diode (1
Through 1) or 13), a circulating current flows in the forward or reverse direction to the high-potential side current detection resistor (4).
Therefore, the amount of circulating current can be detected from the terminal voltage of the current detection resistor (4) on the high potential side. In the present invention, the terminal voltage (4) of the high-potential-side current detection resistor (4) is
Since a) is converted to a low potential side by the level shifter circuit (61) and taken out, it is not necessary to use a large and expensive insulating amplifier.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) In FIG. 1, two pairs of FET type transistors 1A, 1B and 1C, 1D are connected in series as switching transistors (hereinafter simply referred to as transistors), respectively.
It is connected to the. In each of the transistors 1A to 1D, diodes 11, 12, 13, and 14 are formed between the source and the drain, respectively, toward the drain on the high potential side. The motor coil 3 is connected by connecting the connection points of the transistors 1A to 1D of each set to form an H-bridge type coil drive circuit, and between the transistor 1C and the high potential side power supply line L1, and 1D and the low potential side power supply line L2, each transistor 1C,
Current detection resistors 4 and 5 are connected in series with 1D, respectively. The conduction of each of the transistors 1A to 1D is controlled by a signal input from a motor control circuit (not shown) to each gate as described later.

The coil drive circuit having such a configuration is provided with a current detection unit 6, and the current detection unit 6 includes a level shifter circuit 61 and a buffer circuit 62. The level shifter circuit 61 has an operational amplifier 611 and an FET transistor 612 connected to the output side of the operational amplifier 611. The transistor 1C is connected to a non-inverting input terminal of the operational amplifier 611.
And the voltage at the connection point between the current detection resistor 4 and the current detection resistor 4 is input. The inverting input terminal of the operational amplifier 611 is connected to the source of the FET transistor 612. Source of FET type transistor 612 and operating power supply 613 of operational amplifier 611
, A current supply resistor 615 is connected, and the operating power supplies 613 and 614 of the operational amplifier 611 have an intermediate point connected to the high-potential power supply line L1. Thus, one end of the current supply resistor 615 is biased to a positive potential with respect to the high potential side power supply line L1.

The buffer circuit 62 has an operational amplifier 621, and its inverting input terminal has respective resistors 622 and 623.
Are connected at one end. The other end of the resistor 622 is connected to a connection point between the current detection resistor 5 and the transistor 1D, while the other end of the resistor 623 is connected to an output terminal of an operational amplifier 621 that outputs a current detection output. The non-inverting input terminal of the operational amplifier 621 includes voltage dividing resistors 616, 6
The voltage of 17 connection points is input. The other end of the voltage dividing resistor 616 is connected to the drain of the FET transistor 612, while the other end of the voltage dividing resistor 617 is connected to the operational amplifier 6.
21 is connected to an operating power supply 625. Operational amplifier 6
The intermediate point between the operating power supplies 624 and 625 is connected to the low-potential-side power supply line L2.
The other end of 7 is biased to a negative potential with respect to the low potential side power supply line L2. The operating power supplies 613, 614, 624, and 625 of the operational amplifiers 611 and 621 have the same voltage, and the current supply resistor 615 and the voltage dividing resistor 617 have the same resistance value. The resistance value of the voltage dividing resistor 616 is
This is a sufficiently large value as compared with that of 7.

The operation of the thus configured coil drive circuit will be described below. When the motor is stopped, the transistors 1A to 1D are all non-conductive, no current flows to the motor coil 3, and the current passing through the current detection resistors 4 and 5 is zero. Therefore, the terminal voltage 5a of the current detection resistor 5 is equal to the potential of the low potential side power supply line L2 and is 0V.
The output from the operational amplifier 621 due to the terminal voltage 5a is 0V. On the other hand, the terminal potential 4 of the current detection resistor 4
a becomes equal to the potential of the high potential side power supply line L 1, and a predetermined current is supplied by the current supply resistor 615 to the FET transistor 6.
The voltage is supplied to the voltage dividing resistors 616 and 617 through the line 12. Due to this current, a voltage sufficiently lower than the voltage of the driving power supply 2 is generated at both ends of the voltage dividing resistor 617. Since this voltage is offset by the bias from the operating power supply 625, the voltage dividing resistor 61
7, the terminal voltage 617a becomes 0V. Therefore, the output from the operational amplifier 621 due to the terminal voltage 617a is also zero.
V. As a result, the current detection output becomes 0V.

When the motor is rotated forward, the transistors 1B and 1C are turned on. As a result, the current from the drive power supply 2 is supplied to the motor coil 3 via the current detection resistor 4 and the transistor 1C, and returns to the drive power supply 2 via the transistor 1B. At this time, the terminal voltage 4a of the current detection resistor 4 becomes lower than the potential of the high potential side power supply line L1 according to the magnitude of the passing current. As the terminal voltage 4a decreases, the voltage dividing resistors 616, 6
17, the terminal voltage 617a of the voltage dividing resistor 617 rises from 0V, and as a result, the operational amplifier 62
A positive voltage corresponding to the magnitude of the current flowing through the motor coil 3 is output as the current detection output from the motor coil 3. When the transistor 1B becomes non-conductive by the PWM control, the current due to the back electromotive force of the motor coil 3 flows back from the motor coil 3 through the diode 11 to the current detecting resistor 4 and the transistor 1C, so that the motor coil 3 is energized. Flows in the same direction as In this case, the terminal voltage 4a of the current detection resistor 4 becomes lower than the potential of the high-potential-side power supply line L1 in accordance with the magnitude of the return current, and as a current detection output from the operational amplifier 621 in the same process as described above. A positive voltage corresponding to the magnitude of the return current is output.

To reverse the motor, the transistors 1A and 1D are turned on. Thus, the current from the drive power supply 2 is supplied to the motor coil 3 via the transistor 1A, and returns to the drive power supply 2 via the transistor 1D and the current detection resistor 5. At this time, the terminal voltage 5a of the current detection resistor 5 rises above the potential of the low potential power supply line L2 according to the magnitude of the passing current. The terminal voltage 5a is inverted by the operational amplifier 621, and as a result, the operational amplifier 621
A negative voltage corresponding to the current flowing through the motor coil 3 is output as a current detection output from the motor. When the transistor 1D is turned off by the PWM control, a current due to the back electromotive force of the motor coil 3 is supplied from the motor coil 3 to the diode 13D.
Flows back to the current detection resistor 4 and the transistor 1A through
It flows in the motor coil 3 in the same direction as when electricity is supplied. At this time,
In the current detection resistor 4, the terminal voltage 4a rises above the potential of the high potential side power supply line L1 according to the magnitude of the return current. As the terminal voltage 4a rises, the current supply resistance 61
5, the current supplied to the voltage dividing resistors 616 and 617 decreases, and the terminal voltage 617a of the voltage dividing resistor 617 decreases from 0V. As a result, a negative voltage corresponding to the magnitude of the return current at this time is output as a current detection output from the operational amplifier 621.

In this embodiment, the current detection resistors 4 and 5 may be provided on the side of the transistors 1A and 1B.

(Second Embodiment) FIG. 2 shows an example in which the present invention is applied to a so-called T-bridge type coil drive circuit. In the figure, two drive power supplies 2A and 2B are connected in series between a high-potential power supply line L1 and a low-potential power supply line L2, and two transistors 1E and 1F are connected in series with each other. Power supply 2A, 2B and transistor 1
The motor coil 3 is connected between the connection points of E and 1F, and T
A bridge-type coil drive circuit is configured. Diodes 15 and 16 are connected in parallel to the transistors 1E and 1F, respectively, and a current detection resistor 4 is connected between the transistor 1E and the high-potential-side power supply line L1.
A current detection resistor 5 is provided between the power supply line L2 and the low potential side power supply line L2. Then, the terminal voltages 4a and 5a of the current detection resistors 4 and 5 are input to the current detection unit 6 having the same configuration as described in the first embodiment.

In such a coil drive circuit, when the transistor 1E is conducting, a positive current flows through the motor coil 3, and the current value can be known from the terminal voltage 4a of the current detecting resistor 4. Transistor 1E
Becomes non-conducting, the current due to the back electromotive force becomes
Flows in the same direction from the current detection resistor 5 to the diode 16, and the current value of the return current can be known from the terminal voltage 5 a of the current detection resistor 5. on the other hand,
When the transistor 1F is conducting, a current flows in the motor coil 3 in the opposite direction, and the current value is
From the terminal voltage 5a. When the transistor 1F is turned off, a current due to the back electromotive force flows in the motor coil 3 in the same direction. The current returns from the diode 15 to the current detection resistor 4, and the current value of the return current is determined by the terminal of the current detection resistor 4. It can be known from the voltage 4a.

[0019]

As described above, according to the coil drive circuit of the present invention, both the current flowing through the coil and the circulating current due to the coil back electromotive force can be obtained at a low cost without using an expensive insulating amplifier. It can be detected reliably.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an H-bridge type coil drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a T-bridge type coil drive circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of an H-bridge type coil drive circuit showing a conventional example.

FIG. 4 is a circuit diagram of an H-bridge type coil drive circuit showing another conventional example.

[Explanation of symbols]

1A, 1B, 1C, 1D, 1E, 1F... Switching transistors (switching elements), 11, 12, 13,.
14, 15, 16: diode, 2, 2A, 2B: drive power supply, 3: motor coil (coil), 4, 5: current detection resistor, 6: current detection unit, 61: level shifter circuit.

Claims (1)

[Claims] 1. A high-potential-side switching element and a low-potential-side switching element for selectively connecting one end of a coil to a high-potential-side power supply line and a low-potential-side power supply line and supplying forward and reverse current to the coil. And a coil drive circuit having a diode element connected in parallel to each of these switching elements, wherein a current detection resistor is connected in series to at least one of the high-potential-side switching elements and at least one of the low-potential-side switching elements. A coil drive circuit, wherein a terminal voltage of the current detection resistor located on the high potential side is provided via a level shifter circuit.