阅读说明：本技术 电流检测电路及电源装置 (Current detection circuit and power supply device ) 是由 上妻健太郎 杉泽佑树 于 2019-06-11 设计创作，主要内容包括：本发明涉及电流检测电路及电源装置,实现零件个数的削减并高精度地检测电流。电流检测电路(30)检测在DCDC转换器(20)中流动的电流。第一输出部(40)将与来自第一传感器(31)及第二传感器(32)中的检测到大的电流的检测传感器的输出相对应的电压向第三信号通路(L3)施加。而且,第一输出部(40)将相对于来自检测传感器的输出电压而反映了晶体管(41)及晶体管(42)中的与检测传感器连接的元件的电压下降的电压向第三信号通路(L3)施加。第二输出部(50)将相对于向第三信号通路(L3)施加的电压而反映了在晶体管(51)中的基极与发射极之间产生的电压下降的电压向第四信号通路(L4)施加。(The invention relates to a current detection circuit and a power supply device, which can realize the reduction of the number of parts and detect current with high precision. A current detection circuit (30) detects a current flowing in the DCDC converter (20). The first output unit (40) applies a voltage corresponding to the output from the detection sensor that detects a large current, out of the first sensor (31) and the second sensor (32), to the third signal path (L3). The first output unit (40) applies a voltage, which reflects a voltage drop of an element connected to the detection sensor, of the transistor (41) and the transistor (42), to the third signal path (L3), with respect to the output voltage from the detection sensor. The second output unit (50) applies a voltage to the fourth signal path (L4) in which a voltage drop generated between the base and emitter of the transistor (51) is reflected with respect to a voltage applied to the third signal path (L3).)

1. A current detection circuit for detecting a current flowing through a vehicle-mounted DCDC converter electrically connected to a first conductive path and a second conductive path, wherein one of the first conductive path and the second conductive path is an input side conductive path, the other is an output side conductive path, and a voltage applied to the input side conductive path is boosted or reduced and output to the output side conductive path,

the current detection circuit includes:

a first sensor that outputs a first voltage corresponding to a current flowing in the first conductive path;

a first signal path to which a voltage corresponding to the first voltage is applied;

a second sensor that outputs a second voltage corresponding to the current flowing in the second conductive path;

a second signal path to which a voltage corresponding to the second voltage is applied;

a first output unit including a first element having a first input terminal and a first output terminal connected to the first signal path, a second element having a second input terminal and a second output terminal connected to the second signal path, and a third signal path connected to the first output terminal and the second output terminal, the first output unit applying a voltage corresponding to an output from a detection sensor that detects a large current, out of the first sensor and the second sensor, to the third signal path; and

a second output unit including a third element having a third input terminal and a third output terminal connected to the third signal path, and a fourth signal path connected to the third output terminal,

the first output unit applies a voltage reflecting a voltage drop at an element connected to the detection sensor out of the first element and the second element with respect to an output voltage from the detection sensor to the third signal path,

the second output unit applies, to the fourth signal path, a voltage reflecting a voltage drop generated between the third input terminal and the third output terminal in the third element with respect to a voltage applied to the third signal path.

2. The current detection circuit of claim 1,

the first element, the first input terminal, and the first output terminal are respectively configured as a bipolar transistor, a base, and an emitter,

the second element, the second input terminal, and the second output terminal are respectively configured as a bipolar transistor, a base, and an emitter,

the third element, the third input terminal, and the third output terminal are respectively configured as a bipolar transistor, a base, and an emitter.

3. The current detection circuit of claim 1,

the first element, the first input terminal, and the first output terminal are respectively configured as a diode, an anode, and a cathode,

the second element, the second input terminal, and the second output terminal are respectively configured as a diode, an anode, and a cathode,

the third element, the third input terminal, and the third output terminal are respectively configured as a diode, a cathode, and an anode.

4. The current detection circuit according to any one of claims 1 to 3,

the current detection circuit includes:

a first voltage dividing circuit that divides the first voltage applied by the first sensor; and

a second voltage dividing circuit that divides the second voltage applied by the second sensor,

the first input terminal is applied with a voltage divided by the first voltage dividing circuit,

the second input terminal is applied with a voltage divided by the second voltage dividing circuit.

5. A power supply device comprising the current detection circuit according to any one of claims 1 to 4 and the on-vehicle DCDC converter.

Technical Field

The present invention relates to a current detection circuit and a power supply device.

Background

A DCDC converter that boosts or lowers a dc voltage and converts the dc voltage into a desired dc voltage is used as a power supply device for a vehicle. In such a DCDC converter, a configuration capable of accurately detecting the magnitude of a current flowing through a conduction path on the input side and the output side is required. For example, an overcurrent detection circuit disclosed in patent document 1 is configured to apply a voltage obtained by dividing an input voltage of a load device by a diode and a voltage dividing resistor to a base of a transistor as a base bias voltage. When an overcurrent flows through the power supply path and the voltage across the current detection resistor is greater than the voltage across the voltage division resistor, the transistor is biased in the forward direction to be in an on state, and an overcurrent detection signal is transmitted to the power supply device.

[ patent document 1 ] Japanese patent application laid-open No. 9-119949

[ problem to be solved by the invention ]

However, in the configuration of patent document 1, when the currents at a plurality of locations in the circuit are to be detected, it is necessary to provide a plurality of current detection circuits having the same configuration as described above. Specifically, when the currents of the input-side conductive path and the output-side conductive path of the DCDC converter are to be detected, 2 current detection circuits are required because the current detection circuits are provided for the respective conductive paths. For example, as shown in fig. 5, when a current is to be detected based on signals output from sensors provided in different conductive paths, a current detection circuit (a circuit including a resistor, a comparator, and the like) corresponding to each sensor is necessary. Therefore, the number of components increases.

Therefore, as in the current detection circuit shown in fig. 6, it is conceivable to provide a structure including an OR circuit using a diode in which the detection circuit is partially shared among the conductive paths. However, a voltage drop occurs due to the use of the diode, and the voltage drop has a temperature characteristic. Therefore, in a configuration in which the magnitude (threshold) of the detected voltage is set based on the voltage drop of the diode, the threshold fluctuates, and the accuracy of current detection may deteriorate.

Disclosure of Invention

The present invention has been made to solve at least one of the above problems, and an object of the present invention is to provide a structure capable of detecting a current with high accuracy while reducing the number of components.

[ MEANS FOR solving PROBLEMS ] A method for solving the problems

A current detection circuit according to a first aspect of the present invention detects a current flowing through a vehicle-mounted DCDC converter that is electrically connected to a first conductive path and a second conductive path, and that includes an input-side conductive path that is one of the first conductive path and the second conductive path and an output-side conductive path that is the other of the first conductive path and the second conductive path, and that steps up or steps down a voltage applied to the input-side conductive path and outputs the voltage to the output-side conductive path,

the current detection circuit includes:

a first sensor that outputs a first voltage corresponding to a current flowing in the first conductive path;

a first signal path to which a voltage corresponding to the first voltage is applied;

a second sensor that outputs a second voltage corresponding to the current flowing in the second conductive path;

a second signal path to which a voltage corresponding to the second voltage is applied;

a first output unit including a first element having a first input terminal and a first output terminal connected to the first signal path, a second element having a second input terminal and a second output terminal connected to the second signal path, and a third signal path connected to the first output terminal and the second output terminal, the first output unit applying a voltage corresponding to an output from a detection sensor that detects a large current, out of the first sensor and the second sensor, to the third signal path; and

a second output unit including a third element having a third input terminal and a third output terminal connected to the third signal path, and a fourth signal path connected to the third output terminal,

the first output unit applies a voltage reflecting a voltage drop at an element connected to the detection sensor out of the first element and the second element with respect to an output voltage from the detection sensor to the third signal path,

the second output unit applies, to the fourth signal path, a voltage reflecting a voltage drop generated between the third input terminal and the third output terminal in the third element with respect to a voltage applied to the third signal path.

A power supply device according to a second aspect of the present invention includes a vehicle-mounted DCDC converter and the current detection circuit.

[ Effect of the invention ]

In the current detection circuit according to the first aspect, the first output unit applies a voltage corresponding to an output from one of the first sensor and the second sensor, which detects a large current, to the third signal path. Therefore, a voltage corresponding to a current of a conductive path through which a large current flows, among the first conductive path and the second conductive path connected to the DCDC converter, can be applied to the third signal path.

The first output unit applies a voltage reflecting a voltage drop of an element connected to the detection sensor out of the first element and the second element with respect to an output voltage from the detection sensor to the third signal path. The second output unit applies, to the fourth signal path, a voltage reflecting a voltage drop generated between the third input terminal and the third output terminal in the third element with respect to the voltage applied to the third signal path. Therefore, the voltage drop amount of the first element or the second element with respect to the voltage applied to the third input terminal can be cancelled by the voltage drop of the third element. Therefore, the current flowing in the first conductive path or the second conductive path can be detected based on the voltage applied to the fourth signal path without being affected by the voltage drop of the element.

In the current detection circuit, the first sensor and the second sensor detect currents flowing through the first conductive path and the second conductive path connected to the on-vehicle DCDC converter, respectively, and therefore, the currents flowing in different directions through the first conductive path and the second conductive path can be detected. Therefore, the number of components can be reduced as compared with a configuration in which the current detection circuit is provided separately for each of the first conductive path and the second conductive path.

On the basis of this, the temperature change of the voltage drop of the first element or the second element can be offset by the temperature change of the voltage drop of the third element. Therefore, the current can be detected with high accuracy without being affected by the temperature characteristics of the first element or the second element.

According to the power supply device of the second aspect, the same effects as those of the current detection circuit of the first aspect can be obtained.

Drawings

Fig. 1 is a block diagram schematically illustrating the configuration of an in-vehicle power supply system according to embodiment 1.

Fig. 2 is a circuit diagram schematically illustrating the configuration of the current detection circuit of embodiment 1.

Fig. 3 is a circuit diagram schematically illustrating the configuration of a current detection circuit of embodiment 2.

Fig. 4 is a circuit diagram schematically illustrating the configuration of a current detection circuit of embodiment 3.

Fig. 5 is a circuit diagram schematically illustrating the configuration of a current detection circuit of a conventional example.

Fig. 6 is a circuit diagram schematically illustrating the configuration of a current detection circuit of a conventional example.

[ Mark Specification ]

10 … power supply device

15 … first conductive path

16 … second conductive path

20 … DCDC converter for vehicle

30 … current detection circuit

31 … first sensor

32 … second sensor

40 … first output

41 … transistor (first element)

42 … transistor (second element)

50 … second output

51 … transistor (third element)

241 … diode (first element)

242 … diode (second element)

251 … diode (third element)

311 … first voltage divider circuit

321 … second voltage dividing circuit

L1 … first Signal Path

L2 … second Signal Path

L3 … third Signal Path

L4 … fourth Signal Path

Detailed Description

Here, preferred examples of the present invention are shown. However, the present invention is not limited to the following examples.

The first element, the first input terminal, and the first output terminal may be configured as a bipolar transistor, a base, and an emitter, respectively. The second element, the second input terminal, and the second output terminal may be configured as a bipolar transistor, a base, and an emitter, respectively. The third element, the third input terminal, and the third output terminal may be respectively configured as a bipolar transistor, a base, and an emitter.

In this case, the voltage drop variation due to the temperature characteristic of the first element or the second element constituting the bipolar transistor can be canceled by the voltage drop due to the temperature characteristic of the third element constituting the bipolar transistor. Therefore, the current can be detected with high accuracy without being affected by the temperature characteristics of the element.

The first element, the first input terminal, and the first output terminal may be configured to be a diode, an anode, and a cathode, respectively. The second element, the second input terminal, and the second output terminal may be respectively configured as a diode, an anode, and a cathode. The third element, the third input terminal, and the third output terminal may be respectively configured as a diode, a cathode, and an anode.

In this case, the voltage drop variation due to the temperature characteristic of the first element or the second element constituting the diode can be cancelled by the voltage drop due to the temperature characteristic of the third element constituting the diode. Therefore, the current can be detected without affecting the temperature characteristics of the element.

The voltage divider may include a first voltage divider circuit that divides a first voltage applied by the first sensor and a second voltage divider circuit that divides a second voltage applied by the second sensor. The voltage divided by the first voltage dividing circuit may be applied to the first input terminal, and the voltage divided by the second voltage dividing circuit may be applied to the second input terminal.

In this case, the voltage applied to the first element and the voltage applied to the second element can be divided and adjusted by the first voltage dividing circuit and the second voltage dividing circuit, respectively. Also, the degree of magnitude of the detected current may be adjusted between the first conductive path and the second conductive path.

< example 1>

Hereinafter, example 1 embodying the present invention will be described.

The in-vehicle power supply system 100 (hereinafter, also referred to as the system 100) shown in fig. 1 is configured as a power supply system that supplies power to the in-vehicle load 13 (hereinafter, also referred to as the load 13). As shown in fig. 1, the system 100 includes a main power supply unit 11, an auxiliary power supply unit 12, a load 13, a power path 14, a power supply device 10, a control unit, and the like. The main power supply unit 11 is a main power supply source to the load 13. The auxiliary power supply unit 12 is a power supply source different from the main power supply unit 11. The power path 14 is a power supply path between the main power supply unit 11, the auxiliary power supply unit 12, and the load 13. The power supply device 10 includes a DCDC converter 20 (hereinafter, also referred to as a DCDC converter 20) for mounting on a vehicle, a current detection circuit 30, and a control unit 60. The DCDC converter 20 is provided in the power path 14. The current detection circuit 30 detects a current flowing to the DCDC converter 20. The control unit 60 controls operations of the DCDC converter 20, the current detection circuit 30, and the like. The system 100 supplies power from the main power supply unit 11 to the load 13 and the auxiliary power supply unit 12, for example, when the power supply from the main power supply unit 11 is in a normal state, and supplies power from the auxiliary power supply unit 12 to the load 13 and the main power supply unit 11, when the power supply from the main power supply unit 11 is in an abnormal state.

The main power supply unit 11 and the auxiliary power supply unit 12 are configured by known power storage means such as a lead storage battery, a lithium ion battery, an electric double layer capacitor, a lithium ion capacitor, and other power storage units. The main power supply unit 11 and the auxiliary power supply unit 12 electrically connect terminals on the high potential side to the power path 14, and apply an output voltage of a predetermined value (for example, 12V) to the power path 14. The low-potential-side terminals of the main power supply unit 11 and the auxiliary power supply unit 12 are electrically connected to a ground portion provided in the vehicle. The main power supply unit 11 is electrically connected to a generator, not shown, and can be charged with electric power from the generator.

The load 13 is configured as a known electrical component mounted on a vehicle. The load 13 is, for example, an ECU or actuator in a shift-by-wire system, an ECU or actuator in an electronically controlled brake system, or the like. The load 13 operates based on the supply of electric power from the main power supply unit 11 in the above-described normal state, and operates based on the supply of electric power from the auxiliary power supply unit 12 in the above-described abnormal state.

The DCDC converter 20 is a known DCDC converter, and is provided between the main power supply unit 11, the auxiliary power supply unit 12, and the load 13 in the power path 14, as shown in fig. 1. The power path 14 is composed of a first conductive path 15 and a second conductive path 16. The first conductive path 15 has one end connected to the main power supply unit 11 and the other end connected to the DCDC converter 20. The second conductive path 16 has one end connected to the DCDC converter 20 and the other end connected to the auxiliary power supply unit 12. The DCDC converter 20 has the following structure: one of the first conductive path 15 and the second conductive path 16 is an input-side conductive path, and the other is an output-side conductive path, and a dc voltage applied to the input-side conductive path is boosted or reduced and output to the output-side conductive path.

As shown in fig. 1, the current detection circuit 30 is provided in the power path 14 and functions to detect a current flowing through the DCDC converter 20. As shown in fig. 2, the current detection circuit 30 includes a first sensor 31, a second sensor 32, a first signal path L1, a second signal path L2, a first output unit 40, a second output unit 50, resistors 33 to 36, a comparator 37, and the like.

As shown in fig. 1, the first sensor 31 is disposed on the first conductive path 15. The first sensor 31 functions to output a first voltage corresponding to the current flowing through the first conductive path 15. The first sensor 31 has, for example, a resistor and a differential amplifier, and outputs a value indicating a current flowing through the first conduction path 15 (specifically, an analog voltage corresponding to the value of the current flowing through the first conduction path 15). The voltage drop generated in the resistor by the current flowing in the first conduction path 15 is amplified by the differential amplifier and output as a detection voltage (analog voltage) corresponding to the output current.

As shown in fig. 2, the first signal path L1 has one end connected to the first sensor 31 and the other end connected to a base of a transistor 41 described later. The first signal path L1 is applied with the first voltage output by the first sensor 31.

As shown in fig. 1, the second sensor 32 is disposed on the second conductive path 16. The second sensor 32 functions to output a second voltage corresponding to the current flowing in the second conductive path 16. The second sensor 32 has, for example, a resistor and a differential amplifier, and outputs a value indicating a current flowing through the second conduction path 16 (specifically, an analog voltage corresponding to the value of the current flowing through the second conduction path 16). The voltage drop generated in the resistor by the current flowing in the second conduction path 16 is amplified by the differential amplifier and output as a detection voltage (analog voltage) corresponding to the output current.

As shown in fig. 2, the second signal path L2 has one end connected to the second sensor 32 and the other end connected to a base of the transistor 42 described later. The second voltage output by the second sensor 32 is applied to the second signal path L2.

As shown in fig. 2, the first output unit 40 includes a transistor 41, a transistor 42, and a third signal path L3. The transistor 41 corresponds to an example of the first element, and is configured as an NPN-type bipolar transistor. The transistor 41 includes a base, a collector, and an emitter. The base of the transistor 41 corresponds to one example of the first input terminal, and is connected to the other end of the first signal path L1. The collector of the transistor 41 is connected to the constant voltage source Vcc and the collector of the transistor 42. The emitter of the transistor 41 corresponds to an example of the first output terminal, and is connected to one end of the third signal path L3 and the emitter of the transistor 42.

As shown in fig. 2, the transistor 42 corresponds to an example of the second element, and is configured as an NPN-type bipolar transistor. The transistor 42 includes a base, a collector, and an emitter. The base of the transistor 42 corresponds to one example of the second input terminal, and is connected to the other end of the second signal path L2. The collector of the transistor 42 is connected to the constant voltage source Vcc and the collector of the transistor 41. The emitter of the transistor 42 corresponds to an example of the second output terminal, and is connected to one end of the third signal path L3 and the emitter of the transistor 41.

As shown in fig. 2, the third signal path L3 has one end connected to the emitter of the transistor 41 and the emitter of the transistor 42, and the other end connected to one end of the resistor 33. In the third signal path L3, the end of the branched signal path is connected to the base of the transistor 51 described later.

The first output section 40 functions as follows: a voltage corresponding to an output from the detection sensor that detects a large current, of the first sensor 31 and the second sensor 32, is applied to the third signal path L3. Here, when one of the first conductive path 15 and the second conductive path 16 through which a larger current flows is used as a conductive path to be detected, the detection sensor is a sensor connected to the conductive path to be detected.

The resistor 33 has one end connected to the third signal path L3 and the other end electrically connected to ground.

As shown in fig. 2, the second output section 50 is connected to an end of a branched signal path of the third signal path L3. The second output unit 50 includes a transistor 51 and a fourth signal path L4. The transistor 51 corresponds to an example of the third element, and constitutes a PNP-type bipolar transistor. The transistor 51 includes a base, a collector, and an emitter. The base of the transistor 51 corresponds to an example of the third input terminal, and is connected to an end of the branched signal path in the third signal path L3. The collector of the transistor 51 is electrically connected to ground. The emitter of the transistor 51 corresponds to an example of the third output terminal, and is connected to the fourth signal path L4.

As shown in fig. 2, the fourth signal path L4 has one end connected to the emitter of the transistor 51 and the other end connected to one end of the resistor 34. The signal path branched from the fourth signal path L4 is connected to a positive input terminal of a comparator 37 described later.

As shown in fig. 2, the resistor 34 has one end connected to the other end of the fourth signal path L4 and the other end connected to the constant voltage source Vcc.

The comparator 37 is configured as a known comparator. The positive-side input terminal of the comparator 37 is connected to the other end of the fourth signal path L4. The comparator 37 inputs a voltage obtained by dividing the output voltage from the constant voltage source Vcc by the resistors 35 and 36 to the negative input terminal. Specifically, the negative-side input terminal of the comparator 37 is connected to the other end of the resistor 35 having one end connected to the constant voltage source Vcc and to the other end of the resistor 36 having one end electrically connected to the ground. The comparator 37 has an output terminal connected to the control unit 60. The comparator 37 outputs a predetermined high-level signal when the voltage applied to the positive-side input terminal is greater than the voltage (threshold value) applied to the negative-side input terminal. On the other hand, when the voltage applied to the positive input terminal is equal to or less than the voltage (threshold value) applied to the negative input terminal, the comparator 37 outputs a predetermined low-level signal.

The control unit 60 controls the operations of the current detection circuit 30, the DCDC converter 20, and the like. The control unit 60 is configured as a microcomputer, for example, and includes an arithmetic device such as a CPU, a memory such as a ROM or a RAM, and the like. The control unit 60 operates using the electric power supplied from the main power supply unit 11 or the auxiliary power supply unit 12. The control section 60 determines whether or not an overcurrent is generated in the first conductive path 15 or the second conductive path 16 due to grounding or the like based on the signal output from the current detection circuit 30. Specifically, when the comparator 37 outputs a high-level signal, the control unit 60 determines that an overcurrent is generated in the first conductive path 15 or the second conductive path 16. On the other hand, when the comparator 37 outputs a low-level signal, the control unit 60 determines that no overcurrent is generated in the first conductive path 15 and the second conductive path 16. When determining that an overcurrent is generated in the first conductive path 15 or the second conductive path 16, the control unit 60 may perform a predetermined failure notification (perform control such as a notification by sound).

Next, a current detection operation by the current detection circuit 30 will be described.

The control unit 60 controls the DCDC converter 20 to perform an operation of stepping up or stepping down a voltage applied to the input-side conductive path (one of the first conductive path 15 and the second conductive path 16) and outputting the voltage to the output-side conductive path (the other of the first conductive path 15 and the second conductive path 16). The first sensor 31 detects the current flowing through the first conductive path 15, and applies a voltage (first voltage) corresponding to the detected current to the first signal path L1. Similarly, the second sensor 32 detects a current flowing to the second conductive path 16, and applies a voltage (second voltage) corresponding to the detected current to the second signal path L2. The first voltage applied to the first signal path L1 and the second voltage applied to the second signal path L2 are input to the first output unit 40.

The first output unit 40 applies a voltage corresponding to an output from the detection sensor that detects a large current, of the first sensor 31 and the second sensor 32, to the third signal path L3. The first output unit 40 applies a voltage reflecting a voltage drop in the transistor connected to the detection sensor among the transistors 41 and 42 to the output voltage from the detection sensor, to the third signal path L3. That is, the larger one of the first voltage and the second voltage is applied to the third signal path L3 in a state reflecting the voltage drop of the applied transistor.

The second output section 50 applies a voltage reflecting a voltage drop generated between the base and emitter of the transistor 51 with respect to the voltage applied to the third signal path L3 to the fourth signal path L4. Therefore, the voltage drop of the transistor 41 or the transistor 42 with respect to the voltage applied to the base of the transistor 51 can be cancelled by the voltage drop of the transistor 51. Therefore, the current flowing in the first conductive path 15 or the second conductive path 16 can be detected based on the voltage applied to the fourth signal path L4 without being affected by the voltage drop of the transistor 41 or the transistor 42.

The voltage applied to the fourth signal path L4 is applied to the positive-side input terminal of the comparator 37. The comparator 37 compares the voltage applied to the positive input terminal with the voltage applied to the negative input terminal, and outputs the comparison result to the control unit 60. The control section 60 determines whether or not an overcurrent is generated in the first conductive path 15 or the second conductive path 16 based on the comparison result output from the comparator 37.

As described above, since the current detection circuit 30 detects the currents flowing through the first conductive path 15 and the second conductive path 16 connected to the DCDC converter 20 by the first sensor 31 and the second sensor 32, respectively, it is possible to detect the currents flowing in the first conductive path 15 and the second conductive path 16 in different directions. Specifically, in a normal state (a state in which power is supplied from the main power supply unit 11 to the load 13 and the auxiliary power supply unit 12), the current flowing from the main power supply unit 11 to the DCDC converter 20 in the first conductive path 15 can be detected by the first sensor 31, and the current flowing from the DCDC converter 20 to the load 13 and the auxiliary power supply unit 12 in the second conductive path 16 can be detected by the second sensor 32. Thus, the currents flowing from the main power supply unit 11 to the load 13 and the auxiliary power supply unit 12 can be detected in the first conductive path 15 and the second conductive path 16. On the other hand, in an abnormal state (a state where electric power is supplied from the auxiliary power supply unit 12 to the load 13 and the main power supply unit 11), the current flowing from the DCDC converter 20 to the main power supply unit 11 through the first conductive path 15 can be detected by the first sensor 31, and the current flowing from the auxiliary power supply unit 12 to the DCDC converter 20 through the second conductive path 16 can be detected by the second sensor 32. This allows the first conductive path 15 and the second conductive path 16 to detect the current flowing from the auxiliary power supply unit 12 to the load 13 and the main power supply unit 11. Therefore, the number of components can be reduced as compared with a configuration in which the current detection circuit is provided separately for each of the first conductive path 15 and the second conductive path 16.

The current detection circuit 30 is configured to cancel the voltage drop caused in the transistor 41 or the transistor 42 by the voltage drop caused in the transistor 51. Therefore, for example, by making the transistor 41 and the transistor 42 complementary to each other, a temperature change in voltage drop of the transistor 41 or the transistor 42 can be canceled out by a temperature change in voltage drop of the transistor 51. Therefore, the current detection circuit 30 can detect the current with high accuracy without being affected by the temperature characteristics of the transistor 41 or the transistor 42.

Next, the effects of the present configuration are exemplified.

In the current detection circuit 30 described above, the first output unit 40 applies a voltage corresponding to an output from the detection sensor that detects a large current, of the first sensor 31 and the second sensor 32, to the third signal path L3. Therefore, a voltage corresponding to a current of a conductive path through which a large current flows, among the first conductive path 15 and the second conductive path 16 connected to the DCDC converter 20, can be applied to the third signal path L3.

The first output unit 40 applies a voltage reflecting a voltage drop of the element connected to the detection sensor out of the transistors 41 and 42 to the third signal path L3 with respect to the output voltage from the detection sensor. The second output unit 50 applies a voltage reflecting a voltage drop generated between the base and the emitter of the transistor 51 to the fourth signal path L4 with respect to the voltage applied to the third signal path L3. Therefore, the voltage drop of the transistor 51 can be offset by the voltage drop of the transistor 41 or the transistor 42 with respect to the voltage applied to the base of the transistor 51. Therefore, without being affected by the voltage drop of the element, the current flowing in the first conductive path 15 or the second conductive path 16 can be detected based on the voltage applied to the fourth signal path L4.

In the current detection circuit 30, the first sensor 31 and the second sensor 32 detect the currents flowing through the first conductive path 15 and the second conductive path 16 connected to the DCDC converter 20, respectively, and therefore can detect the currents flowing in the first conductive path 15 and the second conductive path 16 in different directions. Therefore, the number of components can be reduced as compared with a configuration in which the current detection circuit 30 is provided separately for each of the first conductive path 15 and the second conductive path 16.

In addition, the temperature change due to the voltage drop of the transistor 51 can be canceled out by the temperature change due to the voltage drop of the transistor 41 or the transistor 42. Therefore, the current can be detected with high accuracy without being affected by the temperature characteristics of the transistor 41 or the transistor 42.

< example 2>

Next, example 2 is explained.