WO2015133295A1

WO2015133295A1 - Constant current circuit

Info

Publication number: WO2015133295A1
Application number: PCT/JP2015/054749
Authority: WO
Inventors: 佑典矢野; 佑樹杉沢; 克馬塚本
Original assignee: 株式会社オートネットワーク技術研究所; 住友電装株式会社; 住友電気工業株式会社
Priority date: 2014-03-05
Filing date: 2015-02-20
Publication date: 2015-09-11
Also published as: JP2015170029A

Abstract

　A constant current circuit (1) is provided with: a first current path in which a current flows from one end of a resistor (R1) and through a resistor (R4) and the collector and emitter of a bipolar transistor (20) in that order; and a second current path in which current flows from outside through an input terminal (T1) and through the collector and emitter of a bipolar transistor (21) in that order. Through the second current path flows a current having a value that is a prescribed number of times greater than the current flowing through the first current path. A microcomputer (10) adjusts the potential on one end of the resistors (R2, R3), respectively, or opens one end up so as to change the amount (Iref) of current flowing through the first current path.

Description

Constant current circuit

The present invention relates to a constant current circuit that draws a constant amount of current from the outside.

Many electric devices are mounted on the vehicle, and a constant current circuit that draws a constant current from the outside is used in order to control power feeding to the electric device or operation of the electric device.

Among such constant current circuits, there is a constant current circuit having a function capable of changing the current drawn from the outside. This constant current circuit is used when the amount of current supplied to an electrical device must be adjusted according to the ambient temperature, or depending on the variation in input / output characteristics of each large-scale electrical device. Used when the amount of current supplied to the device must be fine tuned.

A current mirror circuit is often used for the constant current circuit. In a current mirror circuit composed of an NPN-type first bipolar transistor and an NPN-type second bipolar transistor, the collector and the voltage between the base and the emitter of the first bipolar transistor and the second bipolar transistor, respectively. The amount of current flowing between the emitters changes as well. The current mirror circuit is provided with a first path through which current flows through the collector and emitter of the first bipolar transistor and a second path through which current flows through the collector and emitter of the second bipolar transistor. Further, the bases of the first bipolar transistor and the second bipolar transistor are connected to each other, and the collector and the base are connected in the first bipolar transistor. The emitters of the first bipolar transistor and the second bipolar transistor are grounded.

In the current mirror circuit configured as described above, since the same voltage is applied to the bases of the first bipolar transistor and the second bipolar transistor, a current obtained by multiplying the amount of current flowing through the first path by a predetermined number of times is generated. Flow to the second path. A constant current can be passed through the second path by passing a constant current through the first path.

The constant current circuit described in Patent Document 1 further uses N (N: natural number) bipolar transistors in which the amount of current between the collector and the emitter with respect to the voltage between the base and the emitter changes in the same manner as the second bipolar transistor. Yes. For N bipolar transistors, the collector is connected to the collector of the second bipolar transistor and the emitter is connected to the emitter of the second bipolar transistor. The base of each of the N bipolar transistors is connected to the base of the second bipolar transistor through a switch. Accordingly, N + 1 bipolar transistors including the second bipolar transistor are provided in the second path.

Each of the N bipolar transistors connected as described above operates in the same manner as the second bipolar transistor. For this reason, for example, when the circuit is configured such that the same amount of current as the current flowing in the first path flows between the collector and the emitter of the second bipolar transistor, k (N or less) in the N switches When (natural number) are turned on, an amount of current obtained by multiplying the amount of current flowing through the first path by k + 1 flows through the second path.
In the constant current circuit described in Patent Document 1, the amount of current flowing through the second current path can be changed by adjusting the number of switches to be turned on.

JP-A-6-29758

However, in the constant current circuit described in Patent Document 1, in order to finely control the amount of current flowing through the second path, it is necessary to provide a large number of bipolar transistors by flowing a small amount of current through the first path. Therefore, the constant current circuit described in Patent Document 1 has a problem that the circuit scale increases and the manufacturing cost increases.

Furthermore, since it is necessary to provide a large number of bipolar transistors in which the amount of current between the collector and the emitter with respect to the voltage between the base and the emitter changes in the same manner, there is a problem that the manufacture is difficult.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a small and inexpensive constant current circuit that is easy to manufacture.

The constant current circuit according to the present invention is a constant current circuit in which a predetermined number of times the amount of current flowing through the first current path flows from the outside into the second current path, and the amount of current flowing through the first current path. It is characterized by having a change part which changes.

In the present invention, for example, a current mirror circuit is used so that an amount of current obtained by multiplying the amount of current flowing through the first current path by a predetermined number flows into the second current path from the outside. Then, the amount of current flowing through the first current path is changed. As a result, the amount of current flowing through the second current path is also changed.
Therefore, for example, even when a current mirror circuit is used, only two transistors are required, so that the manufacturing is easy, the circuit scale is small, and the manufacturing is performed at low cost.

The constant current circuit according to the present invention includes a first resistor provided in the first current path, and a second resistor having one end connected to the first current path, and between the both ends of the first current path. A predetermined voltage is applied to the first current path by changing the potential at the other end of the second resistor and opening the other end of the second resistor. The configuration is such that the amount of current flowing in the is changed.

In the present invention, the first resistor is provided in the first current path, and a predetermined voltage is applied between both ends of the first current path. Thereby, a current flows from one end of the first current path through the first resistor. Furthermore, one end of the second resistor is connected to the first current path.

For example, in the case where one end of the second resistor is connected to one end of the first resistor, when the potential at the other end of the second resistor is matched with the potential at the other end of the first resistor, the first resistor and the second resistor A resistor is connected in parallel. Since the combined resistance value of the first resistor and the second resistor connected in parallel is smaller than the resistance value of the first resistor, a large amount of current flows through the first current path. Next, when one end of the second resistor is opened, no current flows through the second resistor. Since the resistance value of the first resistor is higher than the combined resistance value of the first resistor and the second resistor, the resistance value in the first current path increases and the amount of current flowing in the first current path decreases. Further, when the potential at one end of the second resistor is lower than the potential at the other end of the first resistor, a part of the current flowing through the first current path flows through the second resistor. The current flowing through the current further decreases.

As described above, by adjusting either the potential at the other end of the second resistor or opening the other end of the second resistor, the amount of current flowing through the first current path is changed. Therefore, the amount of current flowing through the first current path is easily changed.

In the constant current circuit according to the present invention, a voltage is applied across the first current path, and the changing unit adjusts a height of the voltage to adjust a current flowing through the first current path. It is configured to change the amount.

In the present invention, a voltage is applied to one end of the first current path, whereby a current flows through the first current path. Then, the amount of current flowing through the first current path is changed by adjusting the height of the voltage applied across the first current path. For this reason, it is possible to change the amount of current flowing through the first current path with a simple configuration.

According to the present invention, a small and inexpensive constant current circuit that is easy to manufacture can be realized.

2 is a circuit diagram of a constant current circuit in the first embodiment. FIG. It is explanatory drawing of the operation | movement which a constant current circuit performs. It is an equivalent circuit diagram of the constant current circuit in each output state of the microcomputer. It is an equivalent circuit diagram of the constant current circuit in each output state of the microcomputer. It is an equivalent circuit diagram of the constant current circuit in each output state of the microcomputer. FIG. 4 is a circuit diagram of a constant current circuit in a second embodiment.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit diagram of a constant current circuit according to the first embodiment. This constant current circuit 1 is suitably mounted on a vehicle and includes an input terminal T1. The constant current circuit 1 sucks current from the input terminal T1. The constant current circuit 1 includes a microcomputer (hereinafter referred to as a microcomputer) 10, a current mirror circuit 11, and resistors R1, R2, R3, and R4 in addition to the input terminal T1. The current mirror circuit 11 has NPN-type

bipolar transistors

20 and 21.

The microcomputer 10 has a first end, a second end, a third end, and a fourth end. In the microcomputer 10, the first end, the second end, and the third end are connected to one ends of the resistors R1, R2, and R3, and the fourth end is grounded. A predetermined voltage Vcc, for example, 5 volts is applied to the first end of the microcomputer 10 and one end of the resistor R1. The other end of the resistor R1 is connected to the other ends of the resistors R2 and R3 and one end of the resistor R4.

The other end of the resistor R4 is connected to the collector and base of the bipolar transistor 20 and the base of the bipolar transistor 21. The emitters of the

bipolar transistors

20 and 21 are grounded, and the collector of the bipolar transistor 21 is connected to an input terminal T1 to which current is input from the outside.

The constant current circuit 1 is provided with a first current path through which the current flows from one end of the resistor R1 to the resistor R4 and the collector and emitter of the bipolar transistor 20 in this order. Further, the constant current circuit 1 is provided with a second current path through which current flows from the input terminal T1 in the order of the collector and emitter of the bipolar transistor 21. The resistor R1 provided in the first current path corresponds to the first resistor.

For each of the

bipolar transistors

20 and 21, the amount of current flowing between the collector and the emitter varies in a large / small manner according to the high / low voltage between the base and the emitter. When the same voltage is applied between the base and emitter of each of the

bipolar transistors

20 and 21, the amount of current flowing between the collector and emitter of the bipolar transistor 21 is multiplied by a predetermined number between the collector and emitter of the bipolar transistor 21. Amount of current flows.

In the constant current circuit 1, the voltage Vcc is applied between both ends of the first current path, that is, between one end of the resistor R1 and the emitter of the bipolar transistor 20. Thereby, a current flows through the first current path by applying the voltage Vcc. Since the same voltage is applied to the bases of the

bipolar transistors

20 and 21, a current obtained by multiplying the amount Iref of the current flowing through the first current path by a predetermined number of times is supplied from the outside via the input terminal T 1. Flow into the path.

When the constant current circuit 1 is mounted on a vehicle, the voltage Vcc is generated by a regulator (not shown), for example. The regulator generates a predetermined voltage Vcc from an output voltage of a battery (not shown).

The microcomputer 10 adjusts the potential at one end and opens the one end of each of the resistors R2 and R3 whose other ends are connected to the first current path, so that the current flowing through the first current path is reduced. Change the quantity Iref.
Specifically, the microcomputer 10 applies a voltage Vcc based on the potential of the emitter of the bipolar transistor 20 to one end of each of the resistors R2 and R3, or grounds one end to thereby set the potential at one end. adjust. Each of the resistors R2 and R3 functions as a second resistor.

FIG. 2 is an explanatory diagram of the operation performed by the constant current circuit. The current amount Iref when the microcomputer 10 adjusts and releases the potential described above can be calculated from the circuit shown in FIG. In the circuit shown in FIG. 2, the voltage Vcc is applied to one end of the resistor Ra, one end of each of the resistors R4 and Rb is connected to the other end of the resistor Ra, and the other end of the resistor Rb is grounded. The current mirror circuit 11, the resistor R4, and the input terminal T1 are connected in the same manner as the constant current circuit 1 shown in FIG.

As will be described later, the microcomputer 10 adjusts the potential at one end and opens the one end of each of the resistors R2 and R3, so that the resistance values ra and rb of the resistors Ra and Rb change, and the current amount Iref. Is adjusted. When the resistance value of the resistor R4 is r4 and the voltage between the base and the emitter of the bipolar transistor 20 is Vbe, the current amount Iref is (rb × Vcc− (ra + rb) × Vbe) as shown in FIG. (rb × r4 + ra × r4 + ra × rb) divided by the value.

3, 4, and 5 are equivalent circuit diagrams of the constant current circuit in each output state of the microcomputer 10. The output state that the microcomputer 10 outputs to one end of the resistor R2 is a state where the voltage Vcc is applied to one end of the resistor R2, a state where one end of the resistor R2 is opened, and one end of the resistor R2 is grounded. One of the states. The output state that the microcomputer 10 outputs to one end of the resistor R3 is the same as the output state that the microcomputer 10 outputs to one end of the resistor R2.

In each of the left side, the center, and the right side of FIG. 3, when the voltage Vcc is applied to one end of the resistor R2 while the voltage Vcc is applied to one end of the resistor R3, one end of the resistor R2 is opened. In this case, an equivalent circuit of the constant current circuit 1 is shown in each case and when one end of the resistor R2 is grounded.

When the microcomputer 10 applies the voltage Vcc to one end of the resistor R2 while the voltage Vcc is applied to one end of the resistor R3, as shown in the equivalent circuit shown on the left side of FIG. 3, the resistor Ra shown in FIG. Is a combined resistance of resistors R1, R2, and R3 connected in parallel, and the resistance value of the resistor Rb is infinite.

When the resistance value of the resistor Rb is infinite, the current amount Iref shown in FIG. 2 is expressed by the following equation (1).
Iref = (Vcc−Vbe) / (ra + r4) (1)
The combined resistance value of the resistors R1, R2, and R3 connected in parallel is smaller than the resistance values of the resistors R1, R2, and R3, and further, the combined resistance value of the two resistors R1, R2, and R3 connected in parallel. It is smaller than any of the resistance values of the resistors. For this reason, the current amount Iref is large.

Next, when the microcomputer 10 opens one end of the resistor R2 while the voltage Vcc is applied to one end of the resistor R3, no current flows through the resistor R2. Therefore, as can be seen from the equivalent circuit shown in the center of FIG. 3, the resistor Ra shown in FIG. 2 is a combined resistor of the resistors R1 and R3 connected in parallel, and the resistance value of the resistor Rb is infinite.

As described above, the combined resistance value of the resistors R1, R3 connected in parallel is larger than the combined resistance value of the resistors R1, R2, R3 connected in parallel. Therefore, as can be seen from the equation (1), the current amount Iref when one end of the resistor R2 is opened while the voltage Vcc is applied to one end of the resistor R3 is equal to one end of each of the resistors R2 and R3. Is smaller than the current amount Iref when the voltage Vcc is applied.

Next, when one end of the resistor R2 is grounded in a state where the voltage Vcc is applied to one end of the resistor R3, as shown in the equivalent circuit shown on the right side of FIG. Is a combined resistance of resistors R1 and R3 connected in parallel, and resistor Rb is resistor R2.

In the equivalent circuit shown on the right side of FIG. 3, a part of the current flowing through the first current path flows through the resistor R2. For this reason, when the voltage Vcc is applied to one end of the resistor R3 and the one end of the resistor R2 is grounded, the current amount Iref is the resistance R2 in the state where the voltage Vcc is applied to one end of the resistor R3. The amount is smaller than the current amount Iref when one end is opened.

In each of the left side, the center, and the right side of FIG. 4, when one end of the resistor R2 is open and the voltage Vcc is applied to one end of the resistor R2, the one end of the resistor R2 is open, and The equivalent circuit of the constant current circuit 1 is shown when one end of the resistor R2 is grounded.

When the microcomputer 10 opens one end of the resistor R3, no current flows through the resistor R3. Therefore, when the microcomputer 10 applies the voltage Vcc to one end of the resistor R2 with one end of the resistor R3 open, as shown in the equivalent circuit shown on the left side of FIG. 4, the resistor Ra shown in FIG. The combined resistance of the resistors R1 and R2 connected in parallel, and the resistance value of the resistor Rb is infinite. At this time, the current amount Iref is the largest in a state where one end of the resistor R3 is open.

As described above, the combined resistance value of the resistors R1, R2, and R3 connected in parallel is smaller than the combined resistance value of the resistors R1 and R2 connected in parallel. Therefore, in a state where the voltage Vcc is applied to one end of the resistor R2, the current amount Iref (see the left side of FIG. 3) when the voltage Vcc is applied to one end of the resistor R3 is It is larger than the current amount Iref (see the left side of FIG. 4) when the circuit is opened.

When the microcomputer 10 opens one end of the resistor R3 with one end of the resistor R3 open, as can be seen from the equivalent circuit shown in the center of FIG. 4, the resistor Ra shown in FIG. The resistance value of the resistor Rb is infinite. Since the resistance value of the resistor R1 is larger than the combined resistance value of the resistors R1 and R2 connected in parallel, the current when one end of each of the resistors R2 and R3 is opened is understood from the equation (1). The amount Iref is smaller than the current amount Iref when the voltage Vcc is applied to one end of the resistor R2 in a state where one end of the resistor R3 is open.

The combined resistance value of the resistors R1 and R3 connected in parallel is smaller than the resistance value of the resistor R1. For this reason, in a state where one end of the resistor R2 is open, the current amount Iref (see the center of FIG. 3) when the voltage Vcc is applied to one end of the resistor R3 is open at one end of the resistor R3. It is larger than the current amount Iref in the case (see the center of FIG. 4).

When the microcomputer 10 opens one end of the resistor R3 and grounds one end of the resistor R2, the resistor Ra shown in FIG. 2 is the resistor R1, as can be seen from the equivalent circuit shown on the right side of FIG. The resistor Rb is the resistor R2. In the equivalent circuit shown on the right side of FIG. 4, a part of the current flowing in the first current path flows through the resistor R2. For this reason, the current amount Iref when one end of the resistor R2 is grounded while the resistor R3 is open is smaller than the current amount Iref when one end of each of the resistors R2 and R3 is open. .

The combined resistance value of the resistors R1 and R3 connected in parallel is smaller than the resistance value of the resistor R1. Therefore, in the state where one end of the resistor R2 is grounded, the current amount Iref (see the right side of FIG. 3) when the voltage Vcc is applied to one end of the resistor R3 is such that one end of the resistor R3 is open. In this case, it is larger than the current amount Iref (see the right side of FIG. 4).

In each of the left side, the center, and the right side of FIG. 5, when one end of the resistor R3 is grounded, the voltage Vcc is applied to one end of the resistor R2, the one end of the resistor R2 is opened, and The equivalent circuit of the constant current circuit 1 is shown when one end of the resistor R2 is grounded.

When the microcomputer 10 applies the voltage Vcc to one end of the resistor R2 while the one end of the resistor R3 is grounded, as shown in the equivalent circuit shown on the left side of FIG. 5, the resistor Ra shown in FIG. Is a combined resistance of resistors R1 and R2, and the resistor Rb is a resistor R3. At this time, the current amount Iref is the largest in a state where one end of the resistor R3 is grounded.

When one end of the resistor R3 is grounded, a part of the current flowing through the first current path flows through the resistor R3. Therefore, in the state where the voltage Vcc is applied to one end of the resistor R2, the current amount Iref (see the left side of FIG. 4) when the one end of the resistor R3 is opened is grounded at one end of the resistor R3. In this case, it is larger than the current amount Iref (see the left side of FIG. 5).

When the microcomputer 10 opens one end of the resistor R2 while the one end of the resistor R3 is grounded, the resistor Ra shown in FIG. 2 is the resistor R1, as can be seen from the equivalent circuit shown in the center of FIG. The resistor Rb is the resistor R3. Since the resistance value of the resistor R1 is larger than the combined resistance value of the resistors R1 and R2 connected in parallel, the current amount Iref when one end of the resistor R2 is opened while one end of the resistor R3 is grounded is This is smaller than the current amount Iref when the voltage Vcc is applied to one end of the resistor R2 in a state where one end of the resistor R3 is grounded.

As described above, when one end of the resistor R3 is grounded, a part of the current flowing through the first current path flows through the resistor R3. Therefore, in the state where the resistor R2 is opened, the current amount Iref (see the center of FIG. 4) when one end of the resistor R3 is opened is equal to the current amount Iref when one end of the resistor R3 is grounded. (See the center in FIG. 5).

When the microcomputer 10 grounds one end of the resistor R2 while one end of the resistor R3 is grounded, as can be seen from the equivalent circuit shown on the right side of FIG. 5, the resistor Ra shown in FIG. The resistor Rb is a combined resistor of resistors R2 and R3 connected in parallel. The combined resistance value of the resistors R2 and R3 connected in parallel is smaller than the resistance value of the resistor R3. For this reason, when one end of the resistor R2 is grounded when one end of the resistor R2 is grounded, the amount of current shunted from the first current path is the same as when the one end of the resistor R2 is open. The amount is larger than the amount of current shunted from one current path. Therefore, the current amount Iref when one end of each of the resistors R2 and R3 is grounded is smaller than the current amount Iref when one end of the resistor R2 is opened while one end of the resistor R3 is grounded. is there.

As described above, the resistance value of the resistor R2 is larger than the combined resistance value of the resistors R2 and R3 connected in parallel. For this reason, in a state where one end of the resistor R2 is grounded, the current amount Iref (see the right side of FIG. 4) when one end of the resistor R3 is opened is the current when one end of the resistor R3 is grounded. The amount is larger than the amount Iref (see the right side of FIG. 5).

As described above, in a state where the output state to one end of the resistor R3 is fixed, the current amount Iref when the microcomputer 10 applies the voltage Vcc to one end of the resistor R2 is the largest. Next, the amount of current Iref when the microcomputer 10 opens one end of the resistor R2 is large. The amount of current Iref when the microcomputer 10 grounds one end of the resistor R2 is the smallest.

When the microcomputer 10 changes the output state to one end of the resistor R3 in a state where the output state to one end of the resistor R2 is fixed, the output state to one end of the resistor R3 is also fixed. The state changes in the same manner as when the microcomputer 10 changes the output state to one end of the resistor R2.

In the constant current circuit 1, the microcomputer 10 changes the amount of current Iref by either adjusting the potential at one end and opening at one end of each of the resistors R2 and R3. Since the constant current circuit 1 only needs to include two

bipolar transistors

20 and 21, the constant current circuit 1 can be manufactured easily and inexpensively, and the scale of the constant current circuit 1 is small. In addition, the microcomputer 10 can easily change the amount of current flowing through the first current path by either adjusting the potential at one end or opening the one end of each of the resistors R2 and R3. The microcomputer 10 functions as a changing unit.

The microcomputer 10 can adjust the amount of current flowing from the outside into the second current path via the input terminal T1 by changing the current amount Iref. When the resistance values of the resistors R2 and R3 are different from each other, the number of values of the current amount Iref that can be changed is nine.

Note that the voltage applied by the microcomputer 10 to one end of the resistors R2 and R3 in order to adjust the potential is not limited to the voltage Vcc, and may be a predetermined voltage having a height different from the voltage Vcc. The voltage applied to one end of each of the resistors R2 and R3 may be different. Further, the position where the other ends of the resistors R2 and R3 are connected is not limited to the other end of the resistor R1, and may be connected to the first current path. For example, the other ends of the resistors R2 and R3 may be connected to one end of the resistor R1, and the first end of the microcomputer 10 may be connected to the other end of the resistor R1. In this case, the microcomputer 10 adjusts the potential at one end of each of the resistors R2 and R3, for example, by connecting one end to the other end of the resistor R1 or by grounding one end.

Furthermore, the number of resistors whose other end is connected to the first current path and potential adjustment at one end and opening of the other end are not limited to two, may be one or three or more. The greater the number, the greater the number of values of the current amount Iref that can be changed. Therefore, the microcomputer 10 can adjust the current amount Iref in detail.

(Embodiment 2)
FIG. 6 is a circuit diagram of a constant current circuit according to the second embodiment. The constant current circuit 3 is different from the constant current circuit 1 according to the first embodiment in the configuration for changing the amount of current flowing through the first current path.
In the following, the differences between the second embodiment and the first embodiment will be described. Since the other configuration except the configuration to be described later is the same as that of the first embodiment, the same reference numerals are given and the description thereof is omitted.

The constant current circuit 3 is suitably mounted on a vehicle, like the constant current circuit 1 in the first embodiment, and includes a current mirror circuit 11, a resistor R4, and an input terminal T1. The

bipolar transistors

20 and 21, the input terminal T1, and the resistor R4 of the current mirror circuit 11 are connected as in the first embodiment. The constant current circuit 3 also sucks current from the input terminal T1.

The constant current circuit 3 further includes a microcomputer 30 and a D / A converter 31. The microcomputer 30 is connected to the D / A converter 31, and the D / A converter 31 is connected to one end of the resistor R4.

In the constant current circuit 3, a current path through which the current flows from the one end of the resistor R4 on the D / A converter 31 side in the order of the resistor R4 and the collector and emitter of the bipolar transistor 20 is provided as a first current path. Similar to the first embodiment, the second current path is a current path in which current flows from the input terminal T1 in the order of the collector and emitter of the bipolar transistor 21.

Since the constant current circuit 3 includes the current mirror circuit 11 as in the constant current circuit 1 in the first embodiment, an amount of current obtained by multiplying the amount Iref of the current flowing through the first current path by a predetermined number is externally supplied. , Flows into the second current path via the input terminal T1.

The D / A converter 31 applies a voltage between both ends of the first current path, that is, one end of the resistor R 4 and the emitter of the bipolar transistor 20. Thereby, a current flows through the first current path. The D / A converter 31 receives a digital signal from the microcomputer 30 indicating the voltage level to be applied between both ends of the first current path. The D / A converter 31 applies a voltage having a height indicated by the digital signal input from the microcomputer 30 between both ends of the first current path.
When the voltage applied across the first current path by the D / A converter 31 is Vda, the current amount Iref is calculated by the following equation.
Iref = (Vda−Vbe) / r4

The microcomputer 30 adjusts the height of the voltage Vda by outputting a digital signal indicating various heights to the D / A converter 31 for the voltage applied between both ends of the first current path. Thereby, the microcomputer 30 changes the current amount Iref. The microcomputer 30 functions as a changing unit in the second embodiment.

Similarly to the constant current circuit 1 in the first embodiment, the constant current circuit 3 only needs to include two

bipolar transistors

20 and 21. Therefore, the constant current circuit 3 can be manufactured easily and inexpensively, The scale of the current circuit 3 is small. Further, the current amount Iref is easily changed by the microcomputer 30 adjusting the height of the voltage Vda applied by the D / A converter 31. Therefore, the current amount Iref can be changed with a simple configuration.

The microcomputer 10 can adjust the amount of current flowing from the outside into the second current path via the input terminal T1 by changing the current amount Iref.

The configuration in which the voltage is applied across the first current path is not limited to the configuration in which the D / A converter 31 applies the voltage across the first current path. For example, a battery voltage (not shown) may be applied to various voltages. A configuration in which a DC / DC converter that transforms into a voltage is applied across both ends of the first current path may be employed.

In the first and second embodiments, the current mirror circuit 11 is not limited to the configuration using the two

bipolar transistors

20 and 21. For example, the current mirror circuit 11 may be configured using two FETs (Field-Effect-Transistor). Good. For example, in a configuration using two N-channel FETs, the two FETs are connected in the same manner as the

bipolar transistors

20 and 21. Here, the drain, source, and gate of one FET correspond to the collector, emitter, and base of the bipolar transistor 20, and the drain, source, and gate of the other FET correspond to the collector, emitter, and base of the bipolar transistor 21.

The disclosed embodiments 1 and 2 should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1,3 Constant

current circuit

10,30 Microcomputer (change part)
31 D / A converter R1 resistance (first resistance)
R2, R3 resistance (second resistance)

Claims

In a constant current circuit in which an amount of current that is a predetermined number of times the amount of current flowing in the first current path flows into the second current path from the outside,
A constant current circuit, comprising: a changing unit that changes an amount of current flowing through the first current path.
A first resistor provided in the first current path;
A second resistor having one end connected to the first current path;
A predetermined voltage is applied across the first current path;
The changing unit changes the amount of current flowing through the first current path by adjusting the potential at the other end of the second resistor and opening the other end of the second resistor. The constant current circuit according to claim 1, wherein the constant current circuit is configured as follows.
A voltage is applied across the first current path;
The constant current circuit according to claim 1, wherein the changing unit is configured to change an amount of current flowing through the first current path by adjusting a height of the voltage.