JP2016212005A - Current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection device that can prevent deterioration of accuracy of current detection.SOLUTION: A current detection device comprises: a main element Q1 that includes a first source, first drain, and first gate, and supplies a prescribed current to the first source; a sense element Q2 that includes a second source and second drain, and has the second gate connected to the first gate of the main element, and supplies a current of a ratio of the current flowing to the first source of the main element and the prescribed current to the second source; and potential control units OP and Q3 that make first source potential of the main element and second source potential of the sense element the same potential.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current detection device that detects a current flowing in a circuit.

  2. Description of the Related Art Conventionally, a semiconductor device that relaxes or eliminates variations in overcurrent determination values and temperature dependence is known as a type of current detection device (see Patent Document 1). FIG. 3 is a diagram showing a circuit configuration of a semiconductor device incorporated in a semiconductor power module (not shown). The semiconductor device includes a semiconductor element Q, a current detection resistor R1, a current protection determination circuit 1, a gate drive circuit 2, an overcurrent determination reference power supply 6, and an adjustment resistor R2.

  The semiconductor element Q is composed of, for example, an IGBT element, and has a cell isolation structure that outputs a sense current Is given at a predetermined shunt ratio from the sense terminal 7 with respect to the main current Ic supplied from the input terminal 3 to the collector, Realized as a multi-emitter.

  The gate of the semiconductor element Q is connected to the gate drive circuit 2, and one emitter of the semiconductor element Q functions as a main element and is grounded. The other emitter of the semiconductor element Q functions as a sense element and is grounded via the sense terminal 7 and the current detection resistor R1.

  The current protection determination circuit 1 includes a comparator C1. The voltage V1 of the current detection resistor R1 is input to one input terminal of the comparator C1, and the reference voltage Vref from the overcurrent determination reference power supply 6 is input to the other input terminal. The comparator C1 compares the voltage V1 corresponding to the sense current Is with the reference voltage Vref, and outputs a gate cutoff signal to the gate drive circuit 2 when the voltage V1 becomes larger than the reference voltage Vref.

  When the gate cutoff signal is not input from the current protection determination circuit 1, the gate drive circuit 2 outputs the gate drive signal input from the input terminal 4 to the gate of the semiconductor element Q to turn on the semiconductor element Q. The overcurrent determination reference power supply 6 converts the voltage of the DC power supply 5 into a voltage corresponding to the value set by the adjustment resistor R2, and outputs it as the reference voltage Vref.

  The comparator C1 compares a voltage V1 having a variation for each semiconductor device due to a variation in the current shunting ratio of the sense current Is and a resistance value of the current detection resistor R1, and the reference voltage Vref after being appropriately adjusted by the adjustment resistor R2. Thus, it is determined whether or not the level of the main current Ic has reached the original overcurrent determination level.

  That is, when the comparator C1 detects that the voltage V1 is equal to or higher than the reference voltage Vref only within a predetermined determination time (for example, 10 ms), it determines that the level of the main current Ic is equal to or higher than the overcurrent determination level. Then, the gate cutoff signal is output to the gate drive circuit 2. As a result, the gate drive circuit 2 stops driving the gate of the semiconductor element Q.

JP 2001-197723 A

  However, in the above-described conventional current detection device, the voltage between the gate and the emitter of the main element and the voltage between the gate and the emitter of the sense element are different due to the influence of the current detection resistor R1. For this reason, the operating points of the main element and the sense element are different, and the accuracy of current detection is deteriorated.

  In addition, the current detection device has a high current dependency, and as the main current Ic increases, the voltage difference between the gate-emitter voltage of the main element and the gate-emitter voltage of the sense element increases. Gets worse.

  The subject of this invention is providing the electric current detection apparatus which can prevent the deterioration of the precision of electric current detection.

  In order to solve the above-described problem, a current detection device according to the present invention includes a main element having a first source, a first drain, and a first gate, and supplying a predetermined current to the first source. , A second source, a second drain, and a second gate, the second gate being connected to the first gate of the main element, and a predetermined current flowing through the first source of the main element A sense element that causes a current of a current ratio to flow to the second source, and a potential control unit that sets the first source potential of the main element and the second source potential of the sense element to the same potential. And

  According to the present invention, by setting the first source potential of the main element and the second source potential of the sense element to the same potential, the operating points of the main element and the sense element can be made the same. It is possible to provide a current detection device capable of preventing deterioration in detection accuracy.

It is a figure which shows the structure of the electric current detection apparatus which concerns on Example 1 of this invention. It is a figure which shows the example which applied the electric current detection apparatus which concerns on Example 1 of this invention to the three-phase alternating current generator. It is a figure for demonstrating the conventional electric current detection apparatus.

  Hereinafter, a current detection device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  1 is a diagram illustrating a configuration of a current detection device according to a first embodiment of the present invention. This current detection device includes a battery terminal B, a battery BAT, a main element Q1, a sense element Q2, a field current output terminal F, an operational amplifier OP, a semiconductor element Q3, a current detection resistor VR, an A / D converter 10, and a detected current value. An output terminal C is provided.

  The battery terminal B is used for DC power input / output. The battery terminal B is connected to the positive electrode of the battery BAT, and is connected to the drain of the main element Q1 and the drain of the sense element Q2.

  The battery BAT is made of, for example, a 12-volt storage battery, the positive electrode is connected to the battery terminal B, and the negative electrode is grounded. The battery BAT is charged and discharged via the battery terminal B.

  The main element Q1 is composed of an n-channel power MOSFET that turns on / off a current path to a load (an external element connected to the operational amplifier OP and the field current output terminal F). This n-channel power MOSFET has a source (first source), a drain (first drain), and a gate (first gate).

  The sense element Q2 is composed of an n-channel power MOSFET that turns on / off a current path to a load (the operational amplifier OP and the semiconductor element Q3). This n-channel power MOSFET has a source (second source), a drain (second drain), and a gate (second gate).

  The gates of the main element Q1 and the sense element Q2 are commonly connected, and the drain is commonly connected to the positive electrode of the battery BAT. The main element Q1 and the sense element Q2 form a current mirror circuit with a current ratio (mirror ratio) of 1000: 1. That is, the sense element Q2 allows a current having a predetermined current ratio to flow through the source of the main element Q1.

  The source of the main element Q1 is connected to the non-inverting input terminal of the operational amplifier OP and to the field current output terminal F. The source of the sense element Q2 is connected to the inverting input terminal of the operational amplifier OP and the drain of the semiconductor element Q3 made of a MOSFET.

  The output of the operational amplifier OP is connected to the gate of the semiconductor element Q3, and the source of the semiconductor element Q3 is grounded via the current detection resistor VR. The current detection resistor VR is a variable resistor.

  The operational amplifier OP compares the source potential of the main element Q1 with the second source potential of the sense element Q2. The semiconductor element Q3 is made of, for example, a MOSFET, and controls a current returned to the input of the operational amplifier OP according to the output of the operational amplifier OP. The operational amplifier OP and the semiconductor element Q3 correspond to the potential control unit of the present invention, and set the source potential of the main element Q1 and the source potential of the sense element Q2 to the same potential.

  An A / D converter 10 is connected to a connection point between the source of the semiconductor element Q3 and the current detection resistor VR. The A / D converter 10 converts the voltage at the connection point into a digital signal, and outputs the obtained digital value to the outside through the detected current value output terminal C as a detected current value.

  Next, the operation of the current detection device according to the first embodiment of the present invention configured as described above will be described. In this current detection device, when a current flows through the main element Q1, a current proportional to the current flows through the sense element Q2.

  In this case, the current flowing through the main element Q1 and the sense element Q2 is imaginarily short-circuited via the operational amplifier OP, so that the source potential of the main element Q1 and the source potential of the sense element Q2 become the same potential.

  Thereby, the operating points of the main element Q1 and the sense element Q2 can be made the same, so that the accuracy as the current detection device can be increased. The current from the sense element Q2 is converted into a voltage by the current detection resistor VR, converted into a digital signal by the A / D converter 10, and output from the detection current value output terminal C. The digital signal output from the detected current value output terminal C is read into the electronic control unit (ECU 16, see FIG. 2) and used for current control.

  Specifically, since the mirror ratio of “main element Q1: sense element Q2” is “1000: 1”, when a current of 10 A flows through main element Q1, a current of 10 mA flows through sense element Q2. Flows. In this case, since a current of 10 mA flows through the 200Ω current detection resistor VR, a voltage of 2 V is output. The 2V voltage is converted into a digital signal by the A / D converter 10 and is output from the detected current value output terminal C as a detected current value.

  FIG. 2 is a diagram illustrating an example in which the current detection device according to the first embodiment described above is applied to a three-phase AC generator. Hereinafter, the current detection device will be briefly described. The three-phase AC generator includes a current detection device 11 configured as an IC, an armature coil 12 made of a stator, a field coil 13 made of a rotor, a full-wave rectifier circuit 14, a battery BAT, and an electronic control unit (ECU) 16. It has.

  This three-phase AC generator is driven by an engine (not shown), for example. The field coil 13 is rotated by driving by the engine, and electric power is generated in the armature coil 12. The electric power generated in the armature coil 12 is rectified by the full-wave rectifier circuit 14 and supplied to the battery 15. Thereby, the battery 15 is charged. Further, the power rectified by the full-wave rectification circuit 14 is supplied to the battery terminal B of the power detection device 11.

  The current detection device 11 detects a field current flowing in the field coil of the three-phase AC generator and outputs a field current value to the ECU 16. The ECU 16 controls the field current flowing through the field coil 13 according to the detection result from the current detection device 11. Thereby, the field current value of the three-phase AC generator can be controlled to a predetermined value.

  As described above, according to the current detection device according to the first embodiment, the operating points of the main element Q1 and the sense element Q2 are obtained by setting the source potential of the main element Q1 and the source potential of the sense element Q2 to the same potential. Can be made the same, so that deterioration of current detection accuracy can be prevented.

B Battery terminal F Field current output terminal C Detection current value output terminal Q1 Main element Q2 Sense element Q3 Semiconductor element BAT, 15 Battery OP Operational amplifier VR Adjustment resistor 10 A / D converter 11 Current detection device 12 Armature coil 13 Field magnet Coil 14 Full-wave rectifier circuit 16 Electronic control unit (ECU)

Claims (2)

A main element having a first source, a first drain, and a first gate, and supplying a predetermined current to the first source;
A second source, a second drain, and a second gate, wherein the second gate is connected to the first gate of the main element, and a current flowing through the first source of the main element and a predetermined current A sense element that causes a current of a current ratio to flow to the second source;
A potential control unit for setting the first source potential of the main element and the second source potential of the sense element to the same potential;
A current detection device comprising: The potential controller is
An operational amplifier for comparing the first source potential of the main element and the second source potential of the sense element;
A semiconductor element for controlling a current to be returned to the input of the operational amplifier according to the output of the operational amplifier;
The current detection device according to claim 1, further comprising:

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