JP2007170868A - Current detecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detecting circuit for detecting current flowing in a detection resistor, in which an operational amplifier is made cheap by replacing a differential amplification-use operational amplifier with a comparator-use operational amplifier, and external circuits are reduced to make the cost low. <P>SOLUTION: Three resistance elements are externally connected to the comparator-use operational amplifier fundamentally, and resistance values of the three resistance elements are set appropriately, and a terminal voltage indicative of the current flowing in the detection resistor is differentially amplified, thereby obtaining a value of the flowing current. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a current detection circuit that detects an energization current of a motor, for example, using an operational amplifier.

  Recently, a brushless motor that does not use a rotational position detection sensor of a rotor has been used as an electric motor used in an electric power steering device of an automobile. The brushless motor is configured such that a rectangular wave pulse voltage is applied to a stator winding by an inverter and rotates at a speed synchronized with the rectangular wave pulse voltage (see, for example, Patent Document 1).

  The brushless motor driving apparatus generally includes a current detection circuit for controlling the energization current of the stator winding of the brushless motor. As the current detection circuit, an operational amplifier for differential amplification is used so as to detect a voltage drop based on an energizing current generated between both ends of a detection resistor connected between the ground electrode and one end of the stator winding of the brushless motor. What is configured is known. As shown in FIG. 2, for example, the current detection circuit is connected to the inverting input terminal of the operational amplifier 1 for differential amplification with good direct current characteristics through the input resistors 4 and 5 and one terminal connected to the ground electrode. The other terminal 3 of the detection resistor 2 fixed to is connected. The terminal 3 is connected to the negative side of the inverter that supplies power to the brushless motor. A feedback resistor 8 is connected between an output terminal and a non-inverting input terminal of the operational amplifier 1, an input resistor 9 having one end connected to the ground electrode member and an input to the non-inverting input terminal of the operational amplifier 1. The voltage balance adjusting resistors 10 and 11 and the other end of the capacitor 13 are connected, and a drift adjusting capacitor 14 is connected between the inverting input terminal and the non-inverting input terminal of the operational amplifier 1. 6 and 7 are input voltage balance adjusting resistors.

  In the operational amplifier 1 of the known current detection circuit, in general, it is necessary to perform a high degree of phase compensation in order to improve the direct current characteristics by reducing the bias current and the offset voltage as much as possible. There are many circuit elements to be performed, the circuit configuration is complicated, and the manufacturing cost is high. Further, since the power supply voltage of the operational amplifier 1 for differential amplification of the current detection circuit is generally relatively high, such as several tens of volts, it is necessary to provide a protection circuit 15 for the circuit connected to the output terminal 16 of the current detection circuit. There is a problem that the manufacturing cost of the entire current detection circuit is high.

  Further, the brushless motor drive device generally includes a comparison circuit configured by using an operational amplifier for a comparator for the number of phases in order to control the cycle of the pulse voltage applied to the stator winding of each phase of the brushless motor. Prepare. Each comparison circuit compares a voltage applied to the stator winding detected by a detection resistor connected to one end of the stator winding of each phase with a reference voltage at a neutral point of each stator winding, and the comparison circuit The time when the detected voltage exceeds or falls below the reference voltage is determined at the time when the logic output is switched (see, for example, Patent Document 2).

Although the current detection circuit and the comparison circuit constituting the control circuit of the driving device are mounted on the smallest possible printed circuit board or the like, the occupied space is reduced, but it is still satisfactory. In addition, there is a very high demand for further reduction of the occupied space at the electronic equipment level. In particular, since the three-phase brushless motor drive device includes three comparison circuits corresponding to the three-phase stator windings, the three comparison circuits accommodate four operational amplifiers for comparators in the same package. On the other hand, the current detection circuit is constituted by using one operational amplifier for differential amplification. However, one of the four operational amplifiers in the operational amplifier unit is in an idle state, and there is a problem that the effectiveness of reducing the manufacturing cost and reducing the mounting space is diminished.
JP 2002-51588 A JP 2002-325484 A

  A first object of the present invention is to provide an inexpensive current detection circuit by using an operational amplifier for a comparator instead of an operational amplifier for differential amplification.

  A second object of the present invention is to provide a current detection circuit adapted to match the voltage level of the subsequent circuit connected to the output terminal.

  A third object of the present invention is to use an operational amplifier unit without waste by using one operational amplifier in an operational amplifier unit in which a plurality of operational amplifiers for comparators are accommodated in the same package. A current detection circuit is provided.

  The current detection circuit according to the present invention is a current detection circuit that detects a conduction current with a detection resistor having one end as a fixed potential, an operational amplifier for a comparator, one input terminal of the operational amplifier, and the other end of the detection resistor Connected between the other input terminal of the operational amplifier, the feedback resistor connected between the other input terminal of the operational amplifier and the output terminal of the operational amplifier, and the other input terminal of the operational amplifier and the fixed potential. And a feedback factor setting resistor, wherein an energization current is detected from an output terminal of the operational amplifier.

  In the current detection circuit according to the present invention, one end is connected between the reverse current prevention diode having one end connected to the output terminal of the operational amplifier and the output terminal of the operational amplifier and the reverse current prevention diode. The other end of the resistor having a fixed potential is connected.

  In the current detection circuit of the present invention, the operational amplifier is one of operational amplifier units in which a plurality of operational amplifiers for comparators are accommodated in the same package.

According to the current detection circuit of the first aspect of the present invention, the operational amplifier for the comparator, which is inexpensive in itself, is used, and the current detection circuit is configured at a low cost by reducing the number of external circuit elements. I can do it.
Then, by appropriately setting the resistance values of the three resistance elements, that is, the input resistance, the feedback resistance, and the feedback rate setting resistance, the differential amplifier circuit can be operated using the linear region of the operational amplifier for the comparator. Therefore, the desired current detection is possible.

  According to the current detection circuit of claim 2 of the present invention, the output terminal of the operational amplifier is pulled up (or pulled down) and a diode for preventing a backflow is provided so that the output of the current detection circuit is connected to the subsequent stage. It is possible to eliminate the need for a protection circuit in the subsequent circuit by setting it to be lower than the allowable maximum voltage of the circuit to be operated.

  According to the current detection circuit of the third aspect of the present invention, the remaining operational amplifier in the operational amplifier unit constituting the current detection circuit is used as, for example, a comparison circuit included in the brushless motor driving device. In addition, the operational amplifier unit can be used without waste and the drive device and the like can be manufactured in a compact manner.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram of a brushless motor driving apparatus including a current detection circuit of the present invention.
In FIG. 1, reference numeral 21 denotes a three-phase brushless motor, which is driven by a three-phase pulse current obtained by supplying a DC power source 23 to an inverter 22. The inverter 22 is composed of two electronic switching elements per phase in order to energize the stator windings Lu, Lv, Lw of the three-phase brushless motor 21 bidirectionally, and a total of six electronic switching elements 25u ⁺ , 25u ⁻ , It has a bridge circuit composed of 25v ⁺ , 25v ⁻ , 25w ⁺ and 25w ⁻ . The electronic switching elements ^{25u +, 25u -, 25v +} , 25v -, 25w +, 25w - the switching timing, i.e., the commutation timing of the inverter 22 by controlling on the basis of the logic output of the comparator circuit 50, the three The three-phase brushless motor 21 is rotationally driven at a constant speed while maintaining the repetition cycle of the rectangular wave pulse voltage applied to the stator windings Lu, Lv, Lw of each phase of the phase brushless motor 21 to be constant.

  The detection resistor 32 is connected between the negative electrode of the switching element bridge circuit of the inverter 22 and the ground potential, and the current flowing through the detection resistor 32 is detected by the voltage appearing across the detection resistor 32.

  The current detection circuit 30 includes an operational amplifier 31 for a comparator, an input resistor 34 connected between a non-inverting input terminal of the operational amplifier 31 and a non-ground side terminal 33 of the detection resistor 32, an inverting input terminal of the operational amplifier 31, and A feedback factor setting resistor 36 connected between the ground potential, a feedback resistor 38 connected between the output terminal and the inverting input terminal of the operational amplifier 31, and a reverse current preventing diode connected to the output terminal of the operational amplifier 31. 39 and a resistor 42 for pulling up the output terminal of the operational amplifier 31 to a potential Vcc (for example, 6v). A capacitor 43 is connected to the non-inverting input terminal of the inverting amplifier 31 and a capacitor 44 is connected to the cathode of the diode 39 to reduce high frequency noise. The input resistor 34, the feedback resistor 38, and the feedback factor setting resistor 36 set respective resistance values so that the linear region of the operational amplifier 30 for the comparator is inclined and this region can be used as an amplifier. That is, instead of using the saturation region of the operational amplifier like a comparator, linear amplification is performed using the linear region until reaching the saturation region.

  The voltage indicating the current detection value output from the output terminal of the operational amplifier 31 of the current detection circuit 30 by means of the pull-up resistor 42 is the maximum allowable voltage of the TTL circuit connected to the output side of the current detection circuit 30. For example, it can be suppressed to 6 V or less to match the voltage level of the subsequent circuit.

  The output of the current detection circuit 30 is given to the PWM control unit 63 via the A / D converter 47, for example. The PWM control unit 63 obtains an output torque corresponding to the set value by controlling the amount of current flowing through the stator winding of the three-phase brushless motor 21 so that the current detection value by the current detection circuit 30 becomes the set value.

  The current detection signal from the output terminal of the operational amplifier 31 of the current detection circuit 30 is transferred to a fail safe control unit (not shown), and when the current detection value exceeds the safety reference value, the inverter 22 outputs a three-phase brushless motor. The power supply to 21 can be cut off and used for safety management of an automobile or the like equipped with the drive device.

  The comparison circuit 50 included in the three-phase brushless motor driving apparatus of the present invention is configured using three comparator operational amplifiers 51, 52, and 53 corresponding to the three-phase stator windings Lu, Lv, and Lw, respectively. is there.

  The non-inverting input terminal of the operational amplifier 51 (52, 53) corresponding to the U-phase (V-phase, W-phase) stator winding Lu (Lv, Lw) is connected to the terminal (non-neutral point side) of the stator winding Lu. This corresponds to the potential of the neutral point 28 in which the middle point of the voltage dividing circuit 54 (55, 56) connected to the terminal is connected, and one end of the stator windings Lu, Lv, Lw is commonly connected to the inverting input terminal. A reference voltage power supply 59 for outputting a reference voltage is connected. The output voltage of the reference voltage power supply 5 * 9 is ½ of the output voltage of the DC power supply 23 of the inverter 22. The voltage dividing circuit 54 (55, 56) is a series connection of a winding side resistor having a relatively large resistance value and a ground potential side resistor having a relatively small resistance value.

  The logical outputs Vu (Vv, Vw) of the three operational amplifiers 51 (52, 53) corresponding to the U-phase (V-phase, W-phase) stator windings Lu (Lv, Lw) of the three-phase brushless motor 21 are voltages. The switching pattern determining unit 61 inputs the switching pattern of the voltage applied to each stator winding Lu (Lv, Lw). The determination result is input to the rotational position estimation unit 62, and the estimated rotational position of the rotor of the three-phase brushless motor 21 is calculated based on the switching pattern determination data. The calculated estimated rotational position is given to the PWM control unit 63. The PWM control unit 63 commutates the inverter 22 so that the deviation between the estimated rotation position (corresponding to the switching time of the logic output) and the switching time of the predetermined rectangular wave pulse voltage is zero. A commutation control signal for controlling the output is output. As a result, the three-phase brushless motor 21 is driven to rotate at a constant speed corresponding to the repetition period of the reference rectangular wave pulse voltage. Further, the current flowing through the stator winding Lu (Lv, Lw) is controlled to the set value described above by the duty of the commutation control signal.

  Since the current detection circuit 30 and the three comparison circuits 50 corresponding to the three phases of the three-phase brushless motor 21 are both constituted by the same type of operational amplifier for comparators, the operational amplifier 31 of the current detection circuit 30. The operational amplifiers 51, 52, and 53 of the comparison circuit 50 are integrated with one operational amplifier unit in which four operational amplifiers for comparators are accommodated in the same package without causing any play. Can be made compact.

If the brushless motor to be driven is a single-phase AC motor, one operational amplifier unit that contains two operational amplifiers for comparators in the same package is used for current detection and pattern detection. Can be used. Unlike the above-described embodiments, the present invention can be implemented even if the voltage levels on the ground side and the power supply side are reversed.
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It is a block diagram of the drive device of the brushless motor provided with the current detection circuit of the present invention. It is a circuit diagram of the current detection circuit comprised using the operational amplifier for the conventional differential amplification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Three-phase brushless motor 22 Inverter 23 DC power supply 30 Current detection circuit 31, 51, 52, 53 Comparator operational amplifier 32 Detection resistance 34 Input resistance 36 Feedback rate setting resistance 38 Feedback resistance 39 Diode 42 Resistance for voltage increase 50 Comparison circuit

Claims (3)

In the current detection circuit that detects the energization current with a detection resistor having one end as a fixed potential,
An operational amplifier for a comparator, an input resistor connected between one input terminal of the operational amplifier and the other end of the detection resistor, and a connection between the other input terminal of the operational amplifier and an output terminal of the operational amplifier And a feedback rate setting resistor connected between the other input terminal of the operational amplifier and the fixed potential, and the conduction current is detected from the output terminal of the operational amplifier. Current detection circuit.   Connect the other end of a resistor having one fixed end between the output terminal of the operational amplifier and the diode for preventing reverse current, and the reverse current preventing diode having one end connected to the output terminal of the operational amplifier. The current detection circuit according to claim 1, wherein: 3. The current detection circuit according to claim 1, wherein the operational amplifier is one of operational amplifier units in which a plurality of operational amplifiers for comparators are accommodated in the same package.

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