JP2012149934A - Current detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection circuit in which a difference in current detection accuracy between each of sets of resistances can be absorbed.SOLUTION: In a current detection circuit, a plurality of sets of a shunt resistance and a sense resistance connected to the shunt resistance in parallel, which are provided in a current path, are arranged on a substrate corresponding to a plurality of current paths in which amounts of currents flowing therein have correlation, and each of currents flowing in each of the current paths is detected by using a shunt ratio between the shunt resistance and the sense resistor. In the current detection circuit, each of the shunt resistances and the sense resistances in each of the sets are arranged on the substrate so that temperature differences, which are generated between the shunt resistances and the sense resistances when current detection is performed for the current paths, become equal in each of the sets.

Description

  The present invention relates to a current detection circuit, and in particular, corresponds to a plurality of current paths in which a plurality of sets of shunt resistors provided on a current path and sense resistors connected in parallel to the shunt resistance are correlated. In addition, the present invention relates to a current detection circuit suitable for detecting each current flowing through each current path using a shunt ratio between a shunt resistor and a sense resistor.

  2. Description of the Related Art Conventionally, a current detection circuit that includes a shunt resistor provided on a current path and detects a current flowing through the current path using the shunt resistance is known (see, for example, Patent Document 1). In such a current detection circuit, when a current flows through the shunt resistor in the current path, a voltage corresponding to the amount of current is generated between both ends of the shunt resistor. Therefore, by detecting the magnitude of the voltage generated across the shunt resistor, the current flowing through the current path can be detected based on the voltage and the resistance value of the shunt resistor.

JP 2007-181349 A

  In general, for example, when detecting each of the currents flowing through a plurality of current paths in which the amount of current flowing like each energized phase of the motor correlates, all of the currents flowing through the current paths are accurately detected in order to properly control the motor. It is desirable that it can be detected. Here, since the resistance characteristics vary depending on the temperature, the temperature that acts on the shunt resistor side when detecting the current flowing in each energized phase is detected between the phases in order to accurately detect all of the current flowing in each current path. It is desirable that they are approximately equal. If the temperature acting on the shunt resistor side during the detection of the current flowing through each energized phase differs between the phases, it will be difficult to accurately detect the current flowing through each current path, and as a result, appropriate motor control will be performed. Difficult to do.

  The present invention has been made in view of the above-described points, and an object of the present invention is to provide a current detection circuit capable of absorbing a difference in current detection accuracy between each set.

  The purpose is to provide a plurality of sets of shunt resistors provided on the current path and sense resistors connected in parallel to the shunt resistance, and arranged on the substrate corresponding to the plurality of current paths in which the amount of flowing current is correlated. A current detection circuit that detects each current flowing through each current path by using a shunt ratio between the shunt resistor and the sense resistor, wherein the shunt resistor and the sense resistor of each group are This is achieved by a current detection circuit arranged on the substrate so that a temperature difference generated between the shunt resistor and the sense resistor during path current detection is equal between the groups.

  According to the present invention, it is possible to absorb a difference in current detection accuracy between each set.

It is a block diagram of the current detection circuit which is one Example of this invention. It is a figure showing the temperature coefficients X and Y of the shunt resistance and sense resistance in a present Example. It is the perspective view showing the arrangement position on the board | substrate of the shunt resistance and sense resistance in a present Example. It is a top view showing the arrangement position of a shunt resistor and a sense resistor under a temperature distribution due to heat generation of the shunt resistor in the present embodiment.

  Hereinafter, specific embodiments of a current detection circuit according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration diagram of a current detection circuit 10 according to an embodiment of the present invention. The current detection circuit 10 of the present embodiment is applied to a control circuit for a motor 12 provided in a variable intake system mounted on a vehicle, for example.

  The motor 12 is a three-phase AC motor having a U phase, a V phase, and a W phase. A drive circuit 14 that drives the motor 12 is connected to the motor 12. The drive circuit 14 includes three sets of semiconductor elements 16 and 18 that are provided in correspondence with each of the energized phases U, V, and W of the motor 12. The semiconductor elements 16 and 18 are, for example, MOS type field effect transistors. The semiconductor elements 16 and 18 of the energized phases U, V, and W are connected in series between a power supply terminal 20 to which a predetermined battery voltage VB is applied and a ground terminal 22 to which a vehicle body is connected. Hereinafter, as appropriate, the semiconductor element 16 is referred to as a positive-side semiconductor element 16, and the semiconductor element 18 is referred to as a negative-side semiconductor element 18, respectively. The control circuit of the motor 12 alternately drives a set of semiconductor elements 16 and 18 for each energized phase U, V, and W at an appropriate timing, and performs predetermined driving for the U phase, V phase, and W phase. Switching driving is performed in order.

  When the positive-side semiconductor element 16 is turned on among the semiconductor elements 16 and 18 in each group, a current flows from the power supply terminal 20 to the current-carrying phase of the motor 12 via the positive-side semiconductor element 16. Further, when the negative semiconductor element 18 of the pair of semiconductor elements 16 and 18 is turned on, current flows from the current-carrying phase of the motor 12 to the ground terminal 22 via the negative semiconductor element 18. When such a current flow is appropriately performed in each energized phase U, V, W, the motor 12 operates appropriately.

  A shunt resistor 26 is provided on the current path 24 through which the current flows. The shunt resistor 26 is interposed between the power supply terminal 20 and the positive-side semiconductor element 16, and one shunt resistor 26 is provided for each energized phase U, V, W of the motor 12. The shunt resistor 26 has a predetermined temperature coefficient (for example, 100 ppm / ° C.) X, and has a resistance value (for example, about 3 mΩ) Ro that changes according to the element temperature.

  One end of a sense resistor 28 is connected to the current path 24. Specifically, one end of the sense resistor 28 is connected to the power supply terminal 20, that is, the power supply terminal 20 side terminal of the shunt resistor 26. The sense resistor 28 is provided as a pair of resistors for each shunt resistor 26. The sense resistor 28 has a predetermined temperature coefficient (for example, 150 ppm / ° C.) Y, and has a resistance value (for example, about 12Ω) Rs that changes according to the element temperature. Note that the resistance value Rs of the sense resistor 28 is set to n times (a multiple exceeding “1”, for example, 4000 times) the resistance value Ro of the shunt resistor 26. The temperature coefficient Y of the sense resistor 28 is set to a value larger than the temperature coefficient X of the shunt resistor 26.

  A control ASIC 30 of the current detection circuit 10 is connected to the terminal of the shunt resistor 26 on the semiconductor element 16 side and the other end of the sense resistor 28. The shunt resistor 26 and the sense resistor 28 are connected in parallel between the same point on the current path 24 (specifically, the power supply terminal 20) and the control ASIC 30. The control ASIC 30 has a function of detecting a current Io flowing through the current path 24 of each energized phase based on a current (hereinafter referred to as a sense current) Is flowing through the sense resistor 28.

  The control ASIC 30 makes the potential generated at the other end of the sense resistor 28 (hereinafter referred to as sense output potential Vs) equal to the potential generated at the semiconductor element 16 side terminal of the shunt resistor 26 (hereinafter referred to as shunt output potential Vo). A voltage adjustment unit 32 for adjustment is provided. The control ASIC 30 has a first input terminal 34 to which the semiconductor element 16 side terminal of the shunt resistor 26 is connected, and a second input terminal 36 to which the other end of the sense resistor 28 is connected.

  The voltage adjustment unit 32 includes an operational amplifier 38 having a non-inverting input terminal connected to the first input terminal 34 and an inverting input terminal connected to the second input terminal 36. The output of the operational amplifier 38 is connected to the base of the pnp transistor Q1. The emitter of the pnp transistor Q1 is connected to the inverting input terminal of the operational amplifier 38, and the collector thereof is connected to the base of the npn transistor Q2. The collector of the npn transistor Q 2 is connected to the inverting input terminal of the operational amplifier 38, and the emitter thereof is connected to one end of the resistor 42 via the terminal 40. The other end of the resistor 42 is grounded.

  In the control ASIC 30 described above, the voltage adjustment unit 32 performs a feedback operation so that the sense output potential Vs and the shunt output potential Vo become the same potential. The shunt output potential Vo is input to the non-inverting input terminal of the operational amplifier 38 and the sense output potential Vs is input to the inverting input terminal of the operational amplifier 38.

  When Vs <Vo is established, since (Vo−Vs) is positive, a high signal is output from the output terminal of the operational amplifier 38. In this case, since the base potential of the pnp transistor Q1 is high and no current flows through the base, the pnp transistor Q1 is kept off. Therefore, in such a case, since the base potential of the npn transistor Q2 is low and no current flows through the base, the npn transistor Q2 is kept off. As a result, the collector potential of the npn transistor Q2, that is, the sense output The potential Vs rises at a stretch.

  On the other hand, when Vs> V0 is established, since (Vo−Vs) is negative, a low signal is output from the output terminal of the operational amplifier 38. In this case, since the base potential of the pnp transistor Q1 becomes low and current flows through the base, the pnp transistor Q1 is turned on. When the pnp transistor Q1 is turned on, the base potential of the npn transistor Q2 becomes high and current flows through the base, so that the npn transistor Q2 is turned on. For this reason, in such a case, the sense current Is flows to the resistor 42 via the npn transistor Q2, and the collector potential of the npn transistor Q2, that is, the sense output potential Vs drops at a stretch.

  When the operation of the voltage adjustment unit 32 is repeated in this manner, the sense output potential Vs is adjusted to be substantially the same potential as the shunt output potential Vo. When the shunt output potential Vo and the sense output potential Vs are adjusted to substantially the same potential, the voltage across the shunt resistor 26 and the voltage across the sense resistor 28 are made substantially equal. As described above, the resistance value Rs of the sense resistor 28 is set to n times the resistance value Ro of the shunt resistor 26. Therefore, the current flowing through the shunt resistor 26, that is, the current Io flowing through the current path 24 is n times the sense current Is. In the following, n is the sense ratio (diversion ratio) n.

  The control ASIC 30 includes a voltage across the resistor 42 (specifically, a potential generated at the npn transistor Q2 side terminal of the resistor 42 (= potential output toward the terminal 40)) and a predetermined resistance of the resistor 42. Based on the value, the sense current Is is detected with reference to the following equation (1). Then, the detected current Io flowing through the current path 24 is detected by multiplying the detected sense current Is by a predetermined sense ratio n times (Io = n × Is). The control ASIC 30 detects the current Io flowing through the current path 24 of each energized phase based on the detected sense current Is and the sense ratio n by performing the above-described current detection process for each energized phase.

  FIG. 2 is a diagram showing temperature coefficients X and Y of the shunt resistor 26 and the sense resistor 28 in this embodiment. FIG. 3 is a perspective view showing the arrangement position of the shunt resistor 26 and the sense resistor 28 on the substrate in this embodiment. FIG. 4 is a top view showing the arrangement positions of the shunt resistor 26 and the sense resistor 28 under a temperature distribution due to heat generation of the shunt resistor 26 in this embodiment.

  In general, the characteristics of an element change with a temperature change. For example, the resistance value of the resistor increases as the temperature increases. When the resistance value of the resistor fluctuates, the amount of current flowing changes. At this time, assuming that the rate of change in resistance value with temperature change is different between the shunt resistor 26 and the sense resistor 28, the actual shunt ratio between the current flowing through the shunt resistor 26 and the current flowing through the sense resistor 28 is specified in advance. As a result, the current Io flowing through the current path 24 cannot be accurately detected. Therefore, in order to accurately detect the current Io flowing through the current path 24, it is necessary that the rate of change in the resistance value accompanying the temperature change be equal between the shunt resistor 26 and the sense resistor 28.

  Further, the shunt resistor 26 has a larger amount of heat generation than the sense resistor 28 because a relatively large current for driving the motor 12 flows. In this regard, if the temperature coefficient of the shunt resistor 26 and the temperature coefficient of the sense resistor 28 are equal, the rate of change in the resistance value of the shunt resistor 26 is always larger than the rate of change in the resistance value of the sense resistor 28. As a result, The current Io flowing through the current path 24 cannot be detected with high accuracy. Therefore, in order to accurately detect the current Io flowing in the current path 24, the temperature change of the shunt resistor 26 and the sense resistor so that the resistance value change rate of the shunt resistor 26 and the resistance value change rate of the sense resistor 28 are equal. It is necessary that the temperature coefficients of the resistors 26 and 28 are different from each other so that the temperature change of 28 occurs.

  Further, as in this embodiment, the currents Io flowing through the plurality of current paths 24 in which the amounts of current flowing through the energized phases U, V, and W are correlated are detected, and the motor 12 is appropriately controlled based on the detected currents Io. Therefore, it is desirable that all the currents Io flowing through the current paths 24 of the energized phases U, V, and W can be accurately detected. If the relative temperature environment of the shunt resistor 26 and the sense resistor 28 (for example, the distance between the shunt resistor 26 and the sense resistor 28 on the substrate) differs between the energized phases U, V, and W, the energized phases. Even when the U, V, and W shunt resistors 26 generate heat with the same amount of heat, that is, when the temperature rise due to the heat generation of the current-carrying phases U, V, and W is the same, they act on the sense resistor 28. The temperature to be changed is different between the current-carrying phases U, V, and W, and a difference occurs in current detection accuracy between the current-carrying phases U, V, and W, and the motor control cannot be performed properly. . Therefore, in order not to cause a difference in current detection accuracy between the energized phases U, V, and W, the temperature environment of the shunt resistor 26 and the sense resistor 28 is the same between the energized phases U, V, and W. It is necessary.

  Therefore, in this embodiment, the current Io flowing through the current path 24 over a relatively wide temperature range is detected with high accuracy, and the difference in current detection accuracy between the energized phases U, V, and W is absorbed. It is said.

  In the present embodiment, as described above, the temperature coefficient Y of the sense resistor 28 is set to a value larger than the temperature coefficient X of the shunt resistor 26. For this reason, the sense resistor 28 exhibits a larger resistance value change rate with respect to the same temperature change than the shunt resistor 26, and conversely shows a resistance value change rate equivalent to the shunt resistor 26 with a small temperature change. Even if the temperature of the resistor 26 rises greatly due to heat generation and the temperature of the sense resistor 28 does not rise so much, it is possible to make the resistance value change rate of the sense resistor 28 coincide with the resistance value change rate of the shunt resistor 26. . The “resistance value change rate” is, for example, an increase rate or a decrease rate of the resistance value based on the reference resistance value at room temperature.

  In this embodiment, each element constituting the current detection circuit 10 and the drive circuit 14 is disposed on the substrate 44. The substrate 44 is a substrate having good heat conduction efficiency, such as a ceramic substrate or a glass epoxy substrate. The sense resistor 28 and the shunt resistor 26 constituting the current detection circuit 10 are separated from each other by a predetermined separation distance L on the substrate 44, and the sense resistor 28 generates heat on the substrate 44 due to the drive current to the motor 12. It is arranged at a position to receive heat conduction from the shunt resistor 26. Therefore, the temperature of the sense resistor 28 rises due to the heat generated by the shunt resistor 26, and the temperature rise of the sense resistor 28 corresponds to the temperature rise of the shunt resistor 26 (specifically, from the rise temperature of the shunt resistor 26). Is also increased by a small temperature rise).

  Further, the position of the sense resistor 28 on the substrate 44 described above is related to the rate of change of the resistance value with respect to the temperature rise of the shunt resistor 26 when the current Io flowing through the current path 24 is detected, and the temperature rise of the shunt resistor 26. This is a position where the rate of change of the resistance value with respect to the temperature rise of the sense resistor 28 becomes equal. Conversely, the temperature coefficient X of the shunt resistor 26 and the temperature coefficient Y of the sense resistor 28 are the temperature of the shunt resistor 26 when the current Io flowing in the current path 24 is detected at the position where the sense resistor 28 is disposed on the substrate 44. The resistance value change rate with respect to the rise and the resistance value change rate with respect to the temperature rise of the sense resistor 28 accompanying the temperature rise of the shunt resistor 26 are set to be equal.

  In the configuration of the current detection circuit 10, when the current Io flowing through the current path 24 is detected, the sense resistor 28 increases in temperature according to the temperature increase accompanying the heat generation of the shunt resistor 26, and the resistance value change rate of the shunt resistor 26 is The resistance value change rate of the sense resistor 28 is substantially equal. For this reason, when the current Io flowing through the current path 24 is detected, the shunt ratio between the current flowing through the shunt resistor 26 and the current flowing through the sense resistor 28 can be kept constant, that is, matched to a predetermined sense ratio n. Changes in the diversion ratio can be kept small.

  In the configuration of the current detection circuit 10 described above, the amount of heat generated by the shunt resistor 26 varies in accordance with the amount of current flowing through the shunt resistor 26 when the current in the current path 24 is detected. However, since the temperature rise of the sense resistor 28 corresponds to the temperature rise of the shunt resistor 26, both the resistance value of the shunt resistor 26 and the resistance value of the sense resistor 28 show a constant change with respect to the temperature change. It is possible to make the resistance value change rates of the resistors 26 and 28 substantially equal. Therefore, according to the current detection circuit 10 of the present embodiment, it is possible to accurately detect the current Io flowing through the current path 24 over a relatively wide temperature range.

  In the present embodiment, as described above, the sense resistor 28 is disposed on the substrate 44 at a position that receives heat conduction from the shunt resistor 26 that generates heat by the drive current to the motor 12. The shunt resistor 26 and the sense resistor 28 of each of U, V, and W are arranged so that the distance L between the resistors 26 and 28 on the substrate 44 is substantially equal between the energized phases U, V, and W. Yes. The shunt resistors 26 of the respective energized phases U, V, W have the same temperature coefficient X between the energized phases U, V, W, and the sense resistors 28 of the respective energized phases U, V, W are The energized phases U, V, W have the same temperature coefficient Y.

  For this reason, in the configuration of the current detection circuit 10 described above, the conduction state of the heat generated in the shunt resistor 26 when the current is detected in the current path 24 of each energized phase to the sense resistor 28 is determined by each energized phase U, V, W. The temperature difference between the shunt resistor 26 and the sense resistor 28 is substantially equal between the energized phases U, V, and W. If the temperature difference between the shunt resistor 26 and the sense resistor 28 is equal between the current-carrying phases U, V, W, the temperature rise due to heat generation of the shunt resistor 26 is the same between the current-carrying phases U, V, W. Since the temperature of the sense resistor 28 is the same between the energized phases U, V, W, the actual resistance value of the sense resistor 28 of each energized phase U, V, W is between the energized phases U, V, W. Almost matches. Therefore, according to the current detection circuit 10 of the present embodiment, the energized phases U, V, W are made substantially equal by separating the distances between the shunt resistors 26 and the sense resistors 28 of the energized phases U, V, W. The difference in current detection accuracy between the two can be absorbed, and as a result, the motor 12 can be appropriately controlled.

  Thus, according to the current detection circuit 10 of the present embodiment, the current Io flowing through the current paths 24 of the energized phases U, V, and W of the motor 12 can be accurately detected over a relatively wide temperature range. In addition, the difference in detection accuracy of the current Io flowing through the current path 24 between the energized phases U, V, and W of the motor 12 can be absorbed, so that the rotation of the motor 12 can be performed regardless of the heat generation state of the shunt resistor 26. It is possible to always drive smoothly.

  In the above embodiment, the shunt resistor 26 provided on the current path 24 is interposed between the positive-side semiconductor element 16 and the power supply terminal 20 of the pair of semiconductor elements 16 and 18. The present invention is not limited to this, and may be interposed, for example, between the negative semiconductor element 18 and the ground terminal 22 of the pair of semiconductor elements 16 and 18.

  In the above embodiment, the current Io is detected by the plurality of current paths 24 in which the current amounts in the energized phases U, V, and W of the motor 12 are correlated. However, the present invention is not limited to this. However, the present invention may be applied to a plurality of current paths in which at least the amount of current has a correlation other than the energized phases U, V, W of the motor 12.

DESCRIPTION OF SYMBOLS 10 Current detection circuit 12 Motor 14 Drive circuit 16, 18 Semiconductor element 24 Current path 26 Shunt resistance 28 Sense resistance 30 Control ASIC
32 Voltage adjuster 44 Semiconductor substrate Resistance value of Ro shunt resistor Rs Resistance value of sense resistor Io Current flowing in current path Is Sense current X Temperature coefficient of shunt resistor Y Temperature coefficient of sense resistor

Claims (5)

A plurality of sets of shunt resistors provided on the current path and sense resistors connected in parallel to the shunt resistors are arranged on the substrate in correspondence with the plurality of current paths in which the amount of flowing current has a correlation. A current detection circuit for detecting each of the currents flowing through the shunt resistor by using a shunt ratio between the shunt resistor and the sense resistor,
The shunt resistor and the sense resistor of each group are arranged on the substrate so that the temperature difference generated between the shunt resistor and the sense resistor during current detection of the current path is equal between the groups. A current detection circuit.   The shunt resistor and the sense resistor of each group are arranged on the substrate so that the conduction state of heat generated in the shunt resistor to the sense resistor during current detection of the current path is equal between the groups. The current detection circuit according to claim 1, wherein:   The current detection circuit according to claim 2, wherein a distance between the shunt resistor and the sense resistor of each group on the substrate is the same between the groups.   4. The current detection circuit according to claim 1, wherein a temperature coefficient of the sense resistor is larger than a temperature coefficient of the shunt resistor. 5. 5. The current detection circuit according to claim 1, wherein the plurality of current paths are current paths corresponding to the respective energized phases of the motor.

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