JP3562453B2 - Current detection circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current detection circuit, and more particularly to a current detection circuit that detects a current amount flowing to a load including a motor and various actuators based on a sense current flowing to a sense transistor.
[0002]
[Prior art]
Conventionally, for example, a circuit as shown in FIG. 3 has been known as this type of current detection circuit. Hereinafter, an outline of the configuration and operation will be described.
[0003]
As shown in FIG. 3, the current detection circuit 20 mainly includes a load driving unit 21 that drives the load 50 based on a drive signal Sg output from the control circuit 10, and senses a current flowing through the load 50. It comprises a current detection unit 22 for detecting based on a sense current flowing through the transistor Trs. Here, the load drive unit 21 is configured by a load drive transistor TRd or the like that drives the load 50 based on the drive signal Sg. On the other hand, the current detection unit 22 detects the sense current Is including the sense transistor Trs. It comprises a detection resistor Rs for detection, a voltage adjusting unit 22a for adjusting the source voltage of the transistor Trs to a voltage equal to the source voltage of the load driving transistor TRd, and the like.
[0004]
A MOS field effect transistor is used as the load drive transistor TRd and the sense transistor Trs. Further, transistors having the same electrical characteristics are applied to each of the transistors TRd and Trs, and n times as many transistors as the sense transistors Trs are used as the load driving transistors TRd.
[0005]
The voltage adjustment unit 22a includes a transistor Q1 having a collector-emitter terminal connected between the source terminal of the sense transistor Trs and the detection resistor Rs, and an operational amplifier (op-amp) controlling a base voltage of the transistor Q1. A. The source voltage (sense output) Vos of the sense transistor Trs is input to the non-inverting input terminal of the operational amplifier A, and the source voltage (drive output) of the load driving transistor TRd is input to the inverting input terminal of the operational amplifier A. ) Vod is input. Then, by operating the transistor Q1 according to each of the outputs Vos and Vod, this is adjusted so that the potentials of the outputs Vos and Vod become equal.
[0006]
Next, the operation of the current detection circuit 20 thus configured will be described.
In the current detection circuit 20, the voltage adjustment unit 22a performs a feedback operation so that the sense output Vos and the drive output Vod have the same potential in the following modes (a) and (b).
[0007]
(A) When Vod> Vos At this time, the relationship between the voltages input to each input terminal of the operational amplifier A is
Inverting input terminal voltage (Vod)> Non-inverting input terminal voltage (Vos)
From the output terminal of the operational amplifier A,
Output terminal voltage = non-inverting input terminal voltage (Vos) −inverting input terminal voltage (Vod) (1)
, That is, a negative voltage is output. Therefore, no current is supplied to the base of the transistor Q1, and the transistor Q1 is turned off, so that the collector voltage of the transistor Q1, ie, the source voltage Vos of the sense transistor Trs, rises at a stretch.
[0008]
(B) When Vod <Vos At this time, contrary to the above (a), the relationship between the voltages input to the respective input terminals of the operational amplifier A is:
Inverting input terminal voltage (Vod) <Non-inverting input terminal voltage (Vos)
It becomes. Therefore, a positive voltage having a value according to the above equation (1) is output from the output terminal of the operational amplifier A. That is, a current is supplied to the base of the transistor Q1, and the transistor Q1 is turned on. At this time, a current (sense current) Is flows through the detection resistor Rs, and the collector voltage of the transistor Q1, that is, the source voltage Vos of the sense transistor Trs, decreases.
[0009]
By repeating the operations (a) and (b) in this manner, the sense output Vos is adjusted so as to have substantially the same potential as the drive output Vod. That is, the voltage drop ΔVs (drain-source voltage VDS) caused by the sense transistor Trs is made equal to the voltage drop ΔVd (drain-source voltage VDS) caused by the load driving transistor TRd.
[0010]
In this state, theoretically, the current (load current) IL flowing through the load 50 is n times the sense current Is. That is, from the detection voltage Vd by the detection resistor Rs, the sense current Is is calculated by the following equation: Is = detection voltage Vd / detection resistor Rs (2)
, And the load current IL is obtained as a value obtained by multiplying the sense current Is by n. It should be noted that the exact correspondence is obtained in advance by experiments or the like.
[0011]
[Problems to be solved by the invention]
By the way, generally, the electrical characteristics of a transistor change with its own temperature change. Similarly, the operational characteristics of an operational amplifier including a plurality of transistors are changed by its own temperature change.
[0012]
The elements such as transistors and operational amplifiers are arranged in consideration of the influence of heat.However, due to the misalignment of the elements and the variation in the electrical characteristics, etc., which occur during the manufacture, slight differences in the current detection value may occur. An error may occur. Although this error is slight, when a minute current is detected, the error with respect to the detected value becomes excessive, and the reliability of the detected value decreases.
[0013]
Further, when such a current detection circuit is arranged in a limited narrow range such as an integrated circuit, the ratio occupied by the load driving transistor in the limited range becomes large. For this reason, the other element such as the operational amplifier is naturally provided near the load driving transistor, that is, a part which is easily affected by the heat generated by the transistor. In addition, since the amount of heat generated by the load driving transistor is very large with respect to the heat generated by the other elements, the temperature of the other elements is greatly affected by the heat generated by the transistor. In such a case as well, each element is arranged in consideration of the influence of heat applied to the other elements from the load driving transistor.
[0014]
However, in general, when the distance between the heat source and another element changes near the heat source, the amount of heat received by the element from the heat source also greatly changes.
For this reason, in the above-described integrated circuit in which another element is arranged near the load driving transistor as the heat source, when the arrangement of each element is shifted in the element layout, the amount of heat received by the element from the heat source greatly changes. As a result, the electrical characteristics exhibit characteristics that are significantly different from the desired characteristics. In such a case, the above error increases, and the reliability of the detected value is significantly reduced.
[0015]
Conventionally, as a circuit for detecting a current, for example, a circuit described in Japanese Patent Application Laid-Open No. H7-240884 is also known. These facts are generally common.
[0016]
The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress an error in a detection value caused by the arrangement of each element, and to perform more accurate load current detection. An object of the present invention is to provide a current detection circuit.
[0017]
[Means for Solving the Problems]
Hereinafter, the means for achieving the above object and the effects thereof will be described.
First, according to the first aspect of the present invention, there is provided a voltage adjustment device which receives output voltages from each of a sense transistor and a load driving transistor driven under the same driving conditions and performs feedback control so that the voltages become the same potential. And a current detecting unit for detecting a sense current flowing through the sense transistor, and detecting a current flowing through the load driving transistor connected to a load based on the sense current detected by the current detecting unit. The gist of the detection circuit is that the current detection unit and the voltage adjustment unit are provided in two systems, respectively, and the current detection unit and the voltage adjustment unit are arranged at positions sandwiching the load driving transistor.
[0018]
According to the above configuration, sense currents are respectively detected from the two current detection units. For this reason, even if the arrangement of the elements constituting one of the current detection unit and the voltage adjustment unit is displaced on the element layout, and an error occurs in the sense current due to a change in the electrical characteristics due to the deviation, the sense current is not affected. By detecting the current flowing through the load driving transistor based on the current, the error can be suppressed. In addition, since the current detection unit and the voltage adjustment unit of one system each are provided at the position sandwiching the load driving transistor, when the arrangement of the load driving transistor is shifted on the element layout, the current detection unit and the voltage detection unit are detected from the same transistor. The effect of heat on the unit and the voltage adjustment unit increases in one system and decreases in the other system. That is, as compared to the sense current in the case where there is no shift, the sense current detected in each system has an increased value on one side and a decreased value on the other side. Therefore, if the current flowing through the load drive transistor is detected based on these sense currents, the error can be suppressed by the amount by which the increase and decrease in the sense current are offset. Therefore, it is possible to suppress the error of the detection value caused by the arrangement of each element and detect the load current with higher accuracy. In other words, the degree of freedom of the element layout is increased.
[0019]
According to a second aspect of the present invention, in the current detection circuit according to the first aspect, the two systems of the current detection unit and the voltage adjustment unit are provided at symmetrical positions around the load driving transistor. Make a summary.
[0020]
According to the above configuration, variations in characteristics and operations between the systems in the current detection unit and the voltage adjustment unit of each system are further reduced.
The invention according to claim 3 is the current detection circuit according to claim 1 or 2, further comprising an average value calculation circuit that calculates an average value of the current detected by each of the current detection units. Make a summary.
[0021]
According to the above configuration, even if the sense current detected by each current detection unit varies due to the arrangement of each element, the influence can be avoided with a simpler configuration. Become.
[0022]
According to a fourth aspect of the present invention, in the current detection circuit according to the first or second aspect, the sense transistor and the load driving transistor, and the two-system current detection unit and the voltage adjustment unit are integrally formed by resin molding. The gist of the present invention is that it is formed as an integrated circuit.
[0023]
According to a fifth aspect of the present invention, in the current detection circuit of the third aspect, the sense transistor and the load drive transistor, the two current detection units and the voltage adjustment unit, and the average value calculation circuit are resin-molded. The gist of the present invention is that the integrated circuit is formed as a single integrated circuit.
[0024]
In addition to the configuration according to claim 1 or 2, the configuration according to claim 3 is also a configuration suitable for integration into an integrated circuit as the current detection circuit. The effect will be maximized.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a current detection circuit according to the present invention will be described with reference to FIGS. Note that, in FIG. 1, the same elements as those of the current detection circuit illustrated in FIG. 3 are denoted by the same or corresponding reference numerals, and redundant description of those elements will be omitted.
[0026]
As shown in FIG. 1, in the current detection circuit 2 according to the present embodiment, the above-described current detection unit including the voltage adjustment unit is provided with two systems of a current detection unit 22 and a current detection unit 22 ′. ing. Further, an average value calculation circuit 3 is provided for calculating an average value of the sense currents Is and Is' of the sense transistors Trs and Trs' detected by the respective current detectors 22 and 22 '. The average value calculation circuit 3 is constituted by a well-known circuit such as a circuit that amplifies the respective sense currents Is and Is ′ by そ れ ぞ れ and then adds the amplified sense currents Is and Is ′.
[0027]
The average value calculation circuit 3 is connected to the control circuit 10 via a comparator 31. The comparator 31 selectively outputs an ON signal or an OFF signal to the control circuit 10 based on a comparison between the calculated average value and a predetermined reference voltage Vref.
[0028]
On the other hand, it is assumed that the load 50 driven by the load driving transistor TRd is a motor, and the load current IL is obtained by controlling the signal Sg applied to the load driving transistor TRd by PWM (pulse width modulation) by the control circuit 10. ) Is controlled to increase or decrease. At the same time, the control circuit 10 adjusts the load current IL by modulating the pulse width of the signal Sg according to the output signal of the comparator 31.
[0029]
On the other hand, as shown in FIG. 2, in the present embodiment, the current detection circuit 2 and the average value calculation circuit 3 include the transistor array 4 including the load drive transistor TRd and the sense transistors Trs and Trs ′. Are formed as a resin-molded integrated circuit 60. A MOS field effect transistor is used for each of the sense transistors Trs and Trs' and the load driving transistor TRd.
[0030]
In the present embodiment, the transistor array 4 is arranged at the center of the integrated circuit 60. For example, one of the transistors constituting the transistor array 4 at each end is used as sense transistors Trs and Trs', and the other transistors are used. Transistors are used as load drive transistors TRd.
[0031]
Further, in the integrated circuit 60, the current detecting sections 22 and 22 'are arranged symmetrically at positions sandwiching the transistor array 4 which is mostly composed of the load driving transistors TRd. For this reason, at the time of driving, even if the temperature of the current detectors 22 and 22 ′ changes due to the heat generated from the load driving transistor TRd and the characteristics change, the variation in the characteristics is reduced. . Moreover, in the present embodiment, since the average value calculating circuit 3 is provided, even if the characteristics between the current detection units 22 and 22 'vary, the influence is not affected by the average value. The calculation circuit 3 naturally cancels out.
[0032]
As described above, according to the present embodiment, the following effects can be obtained.
(1) Since the two current detectors 22 and 22 'are provided, the load current IL is detected based on the sense currents Is and Is' detected by the respective current detectors 22 and 22'. Therefore, even if the arrangement of the elements constituting one of the current detection sections is shifted in the element layout, it is possible to suppress the error caused by this shift. In addition, since the current detectors 22 and 22 'are arranged symmetrically at positions sandwiching the transistor array 4 which is mostly composed of the load driving transistor TRd, the currents generated by the load driving transistor TRd are reduced. Even if the temperature of the detectors 22 and 22 'changes, it is possible to reduce variations in the characteristics. Therefore, it is possible to suppress the error of the detection value caused by the arrangement of each element and detect the load current with higher accuracy.
[0033]
(2) Since the average value calculation circuit 3 for calculating the average value of each of the sense currents Is and Is' detected by each of the current detection units 22 and 22 'is provided, even if each of the current detection units 22 and 22' is provided. Even if there is a variation in the characteristics between them, the influence can be offset by a well-known simple configuration such as the average value calculation circuit 3.
[0034]
(3) The current detection circuit 2 and the average value calculation circuit 3, including the transistor array 4 including the load drive transistor TRd and the sense transistors Trs and Trs', are formed as an integrated resin-molded integrated circuit 60. . Since the current detection circuit 2 and the average value calculation circuit 3 have a configuration suitable for integration into an integrated circuit, the effects described in the above (1) and (2) can be maximized.
[0035]
The above embodiment can be modified and implemented as follows.
In the above embodiment, the MOS field effect transistor is used as the sense transistor Trs and the load driving transistor TRd. However, a field effect transistor other than the MOS type or a bipolar transistor may be used. Good.
[0036]
In the above embodiment, the average value calculation circuit 3 for calculating the average value of the two sense currents Is and Is' is provided. However, the average value calculation circuit 3 is not necessarily required. Alternatively, the control circuit 10 may implement the variation cancellation operation on a program.
[0037]
In the above embodiment, the transistor array 4, the current detection circuit 2, and the average value calculation circuit 3 are formed as an integrated integrated circuit 60 molded with resin. However, the transistor array 4, the current detection circuit 2, and the The average value calculation circuit 3 may be formed on a substrate, for example.
[0038]
In the above embodiment, each of the current detectors 22 and 22 ′ is arranged symmetrically at a position sandwiching the transistor array 4, which is mostly composed of the load driving transistor TRd, but the transistor array 4 is sandwiched. If it is a position, each of these current detectors 22 and 22 'may be disposed at an asymmetric position. According to such a configuration, when the arrangement of the load driving transistor TRd is shifted in the element layout, the influence of heat on the current detection units 22 and 22 ′ from the transistor TRd increases in one system and increases in the other system. It decreases in the system of. That is, one of the sense currents Is and Is' output from each of them outputs an increased value and the other outputs a decreased value. Therefore, by detecting the load current IL based on the sense currents Is and Is', the increase and decrease in the sense current can be offset, and the error can be suppressed. .
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a circuit configuration of an embodiment of a current detection circuit according to the present invention.
FIG. 2 is an exemplary plan view showing a layout of the current detection circuit of the embodiment as an integrated circuit;
FIG. 3 is a circuit diagram showing a circuit configuration of a conventional current detection circuit.
[Explanation of symbols]
2, 20: current detection circuit, 3: average value calculation circuit, 4: transistor array, 10: control circuit, 21: load drive unit, 22, 22 ': current detection unit, 22a, 22a': voltage adjustment unit, 31 ... Comparator, 50 ... Load, 60 ... Integrated circuit, A, A '... Op amp, Q1, Q1' ... Transistor, Rs, Rs '... Detection resistor, TRd ... Load drive transistor, Trs, Trs' ... Sense transistor.

Claims (5)

A voltage adjustment unit that inputs the output voltage from each of the sense transistor and the load drive transistor driven under the same drive condition and performs feedback control so that the voltages become the same potential; and a sense current that flows through the sense transistor. A current detection circuit that detects a current flowing through the load driving transistor connected to a load based on a sense current detected by the current detection unit.
A current detection circuit comprising two systems each of the current detection unit and the voltage adjustment unit, and the current detection unit and the voltage adjustment unit are arranged at positions sandwiching the load driving transistor. 2. The current detection circuit according to claim 1, wherein the two systems of the current detection unit and the voltage adjustment unit are provided symmetrically with respect to the load driving transistor. 3. The current detection circuit according to claim 1 or 2,
A current detection circuit further comprising an average value calculation circuit that calculates an average value of the current detected by each of the current detection units. The current detection circuit according to claim 1 or 2,
The current detection circuit, wherein the sense transistor and the load driving transistor, and the two systems of the current detection unit and the voltage adjustment unit are formed as an integrated resin-molded integrated circuit. The current detection circuit according to claim 3,
The current detection circuit, wherein the sense transistor and the load drive transistor, the two systems of the current detection unit and the voltage adjustment unit, and the average value calculation circuit are formed as a resin-molded integrated circuit.

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