JPH1168533A - Current detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit that can stably perform highly precise current detection. SOLUTION: This circuit is equipped with an output transistor 1, in which a drain and a source are serially connected to a current path to an electric charge L, and a transistor 2 for current detection, which is not connected in series to the output transistor 1, and in which the drain is connected to a corrector of the first transistor 5a and the source is connected to a terminal 24 of a grounding potential, and it is constituted so that a current 11 running through the transistor 1 is detected on the basis of a current I3 which runs through the second transistor 5b which composes a current mirror circuit 5 together with the first transistor 5a. An equal drive voltage is applied between each of the gate sources of the transistors 1 and 2 by the drive circuits 3 and 4, and a mitter voltage of the first transistor 5a is adjusted by a voltage control circuit 6, so that a voltage between drain-sources of both transistors 1 and 2. As a result, even if a same phase noise occurs to the drain and the source of the transistor 1, the voltage between the drain-source of the transistor 2 will not change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a current detection circuit for detecting a current flowing through an output transistor.

[0002]

2. Description of the Related Art Conventionally, a current detecting circuit of this type has been disclosed in U.S. Pat. No. 5,081,379 and JP-A-62-24.
There is one disclosed in Japanese Patent No. 7268. That is, in the current detection circuit disclosed in the above publication, as shown in FIG. 5, the drain is connected to the power supply voltage (high potential side of the DC power supply) VD, and the source is connected to the ground potential (low potential of the DC power supply) via the electric load L. And an output transistor Q1 composed of an N-channel MOS transistor connected to the output transistor Q1 and having the same type and the same polarity as the output transistor Q1 (that is, an N-channel MOS transistor). A drain and a source are connected in series with a current path between a current detection transistor Q2 commonly connected to a drain and a gate of the transistor Q1, and a source and a ground potential of the current detection transistor Q2. And an N-channel MOS transistor Q4 connected to each other, and a current And N-channel MOS transistor Q5 constituting the over circuit, and a.

Further, the current detection circuit disclosed in the above publication has a non-inverting input terminal (+ terminal) as a means for matching the source voltage of the current detection transistor Q2 to the source voltage of the output transistor Q1. Q
1, the operational amplifier OP having an inverting input terminal (-terminal) connected to the source of the current detection transistor Q2, the source of the current detection transistor Q2 and the MO.
Between the drain of the S transistor Q4, a voltage control transistor Q3 composed of a P-channel MOS transistor having a source and a drain connected in series and a gate connected to the output terminal of the operational amplifier OP is provided.

In this current detection circuit, a common gate voltage is applied to both gates of the output transistor Q1 and the current detection transistor Q2, so that both transistors Q1
When a current flows through Q1 and Q2, the drain-source voltage of the voltage control transistor Q3 driven by the output of the operational amplifier OP matches the source voltage of the current detection transistor Q2 and the source voltage of the output transistor Q1. To change.

Therefore, the potential differences between the terminals of the output transistor Q1 and the current detection transistor Q2 are all equal, and the current flowing through the output transistor Q1 (ie, the load flowing through the electric load L) is applied to the current detection transistor Q2. Current) IQ1 and the current detection transistor Q
The current IQ2 corresponding to the ratio of the transistor size of the transistor 2 to the output transistor Q1 flows accurately, and the current IQ2 flows to the MOS transistor Q4 via the voltage controlling transistor Q3.

Then, a current i, which is a predetermined multiple of the current IQ2 flowing through the current detecting transistor Q2, flows through the MOS transistor Q5 forming a current mirror circuit together with the MOS transistor Q4. The current IQ1 flowing through the output transistor Q1 is detected based on the current i flowing through the transistor Q5.

That is, in the above-described conventional current detection circuit, the drain of the output transistor Q1 and the drain of the current detection transistor Q2 connected in series to a current path for flowing a current to the electric load L are commonly connected. A voltage equivalent to the source voltage of the output transistor Q1 is applied to the source of the current detection transistor Q2 by the operational amplifier OP and the voltage control transistor Q3 so that the drain-source voltages of both transistors Q1 and Q2 are matched.
As a result, the current IQ1 flowing through the output transistor Q1 can be accurately detected.

[0008]

However, in the above-described conventional current detection circuit, when a steep in-phase voltage fluctuation occurs between the drain and the source of the output transistor Q1 due to noise or the like, the voltage between the drain and the source of the output transistor Q1 is reduced. In spite of the fact that the voltage has not changed, the voltage between the drain and the source of the current detection transistor Q2 has changed, and there is a problem that high-precision current detection cannot be performed stably.

More specifically, in the above-described conventional current detection circuit, when a steep voltage fluctuation (hereinafter referred to as noise) occurs on the drain side of the output transistor Q1, the drain of the current detection transistor Q2 is connected to the output transistor Q1.
1, the noise is generated also at the drain of the current detection transistor Q2.

Here, since the operation speed of the output transistor Q1 is relatively high, noise having the same phase as the above-mentioned noise also occurs at the source of the output transistor Q1. ,
The potential difference between the drain and the source) hardly changes.

On the other hand, the current detecting transistor Q2
Is configured to be adjusted by the operational amplifier OP and the voltage control transistor Q3, when the source voltage of the output transistor Q1 fluctuates due to noise, the operational amplifier OP and the voltage control transistor Q3 It operates so that the source voltage of the transistor for use Q2 matches the source voltage of the output transistor Q1.

However, the operating speed of the circuit portion including the operational amplifier OP and the voltage controlling transistor Q3 is generally slower than the operating speed of the output transistor Q1, so that the drain-source voltage of the output transistor Q1 remains unchanged. Nevertheless, the drain-source voltage of the current detection transistor Q2 changes, and as a result,
The detected value of the current becomes unstable.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a current detection circuit that can stably perform high-precision current detection without being affected by noise.

[0014]

In the current detection circuit of the present invention, two output terminals of an output transistor are connected in series to a current path for flowing a current to an electric load. A current detection transistor having the same type and the same polarity as the output transistor and not directly connected to the output transistor is provided. One output terminal of the current detection transistor is connected to a predetermined potential, and the other output terminal is connected to a predetermined potential. The terminal is connected to one terminal of the current path forming element.

Further, a terminal of the current path forming element opposite to the current detecting transistor, both output terminals of the output transistor, and both output terminals of the current detecting transistor are connected to a voltage control circuit. The voltage control circuit includes a current detection transistor of the current path forming element such that a potential difference between both output terminals of the current detection transistor is a predetermined multiple of a potential difference between both output terminals of the output transistor. The potential of the terminal on the opposite side is changed.

Incidentally, the same kind and the same polarity means that, for example, if the output transistor is an N-channel MOS transistor,
The current detecting transistor is also an N-channel MOS transistor, and the output transistor is a PNP transistor (P
In the case of an NP-type bipolar transistor, this means that the current detection transistor is also a PNP transistor.

As described above, in the current detection circuit of the present invention, the voltage control circuit controls the current difference so that the potential difference between the two output terminals of the current detection transistor becomes a predetermined multiple of the potential difference between the two output terminals of the output transistor. The potential of the terminal of the path forming element opposite to the current detecting transistor is adjusted.

Therefore, for example, the predetermined multiple is set to 1 (that is, the voltage control is performed so that the potential difference between both output terminals of the current detection transistor is the same as the potential difference between both output terminals of the output transistor). The operation characteristics of the circuit are set in advance), and each of the output transistor and the current detection transistor is driven such that the potential difference between the control terminal of the two transistors and one output terminal becomes the same, and both of them are driven. If a current flows through the transistor, the potential difference between all terminals of the output transistor and the current detection transistor becomes equal, so that the current flowing through the output transistor (that is, the load current flowing through the electric load) is provided to the current detection transistor. ), The current corresponding to the transistor size ratio between the current detection transistor and the output transistor is accurately calculated. Will be, flows the current in the current path forming element.

The current flowing between the two output terminals of the output transistor is accurately detected based on the current flowing through the current path forming element via the current detecting transistor. Here, in particular, in the current detection circuit of the present invention, the output transistor and the current detection transistor are not directly connected, and the voltage (absolute potential) of the output terminal of the current detection transistor is not controlled. The voltage difference between the two output terminals of the current detection transistor is controlled by the voltage control circuit according to the potential difference between the two output terminals of the output transistor. When this occurs, that is, in a situation where the absolute potential of the output terminal of the output transistor changes but the potential difference between the two output terminals does not change, the voltage control circuit does not substantially operate, and the two output terminals of the current detection transistor do not. The potential difference between them does not change.

Therefore, according to the current detection circuit of the present invention,
When a steep in-phase voltage fluctuation occurs at both output terminals of the output transistor, the potential difference between both output terminals of the current detection transistor changes even though the potential difference between both output terminals of the output transistor does not change. This eliminates the drawbacks of the conventional circuit such as that of the conventional circuit, and enables stable current detection with high accuracy without being affected by noise.

In the above description, the case where the voltage control circuit matches the potential difference between both output terminals of the current detection transistor with the potential difference between both output terminals of the output transistor has been described. The ratio of the potential difference between the output terminals to the potential difference between the two output terminals of the output transistor (the predetermined multiple) may be set to a value other than 1 depending on the characteristics of the output transistor and the current detection transistor. .

On the other hand, in the above description, the control terminals of the output transistor and the current detection transistor are gates when both transistors are MOS transistors as described in claim 3, and both transistors are the same. In the case of a bipolar transistor as described in (1), it is a base.

Further, in order to drive each of the output transistor and the current detecting transistor so that the potential difference between the control terminal and one of the output terminals is equal to each other, it is preferable that the output transistor and the current detection transistor be driven in the same manner. The configuration may be as follows. That is, when a MOS transistor is used as the output transistor and the current detection transistor, the output transistor has a gate and a source connected between the gate and the source of the output transistor. What is necessary is just to provide a first drive circuit for applying a drive voltage and a second drive circuit for applying a drive voltage equivalent to the drive voltage between the gate and the source of the current detection transistor. According to the current detection circuit of the fourth aspect, while the gate-source voltage of the output transistor and the gate-source voltage of the current detection transistor are matched, both of the transistors are driven independently. be able to.

In the case where a bipolar transistor is used as the output transistor and the current detecting transistor, the base and the emitter of the output transistor are connected to each other as in the current detecting circuit according to the sixth embodiment. A first drive circuit may be provided between the base and the emitter of the current detecting transistor, and a second drive circuit may be provided between the base and the emitter of the current detection transistor. According to the current detection circuit of the sixth aspect, the base-emitter voltage of the output transistor and the base-emitter voltage of the current detection transistor are matched, and both transistors are independently driven. be able to.

A specific and preferred configuration of the voltage control circuit is as described in claim 2. That is, in the current detection circuit according to the second aspect, the voltage control circuit is configured to control the voltage of the output terminal on the high potential side of the two output terminals of the output transistor and the low potential side of the output terminals of the current detection transistor. A first resistor and a second resistor that divide the voltage of the output terminal of the output transistor, and a voltage of the output terminal on the low potential side of both output terminals of the output transistor and a high voltage of both output terminals of the current detection transistor. A third resistor and a fourth resistor for dividing the voltage of the output terminal on the potential side; and an operational amplifier, wherein the operational amplifier has a voltage divided by the first resistor and the second resistor. It is configured to change the potential of the terminal of the current path forming element opposite to the current detecting transistor so that the voltage and the voltage divided by the third resistor and the fourth resistor match. .

According to the current detecting circuit of the second aspect, the operation of the voltage control circuit can be realized with a simple circuit configuration, and the potential difference between the two output terminals of the current detecting transistor can be reduced. The ratio with respect to the potential difference between the two output terminals of the output transistor (the predetermined multiple) can be easily set by the resistance values of the first to fourth resistors.

On the other hand, in the current detection circuit of the present invention,
For example, a resistor having a predetermined resistance value is used as a current path forming element, and a current flowing between both output terminals of an output transistor is detected by measuring a potential difference generated between both ends of the resistor. can do.

According to a seventh aspect of the present invention, as the current path forming element, one output terminal is connected to the output terminal of the current detecting transistor opposite to the predetermined potential, and the other output terminal is connected to the other terminal. A first transistor which is connected to the voltage control circuit and forms a part of a current mirror circuit;
And the current mirror circuit may be configured together with the first transistor to provide a second transistor that allows a current proportional to the current flowing through the first transistor to be provided.

That is, in the current detecting circuit according to the seventh aspect, the current flowing through the first transistor as a current path forming element (ie, the current flowing through the current detecting transistor) is provided in the second transistor. ) Flows, and therefore, by measuring the current flowing through the second transistor, the current flowing between both output terminals of the output transistor can be accurately detected.

In the current mirror circuit, the ratio between the current flowing through the first transistor and the current flowing through the second transistor is determined by the current mirror ratio of the current mirror circuit which is determined by the transistor sizes of the first and second transistors. And can be appropriately set to various values.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. It is needless to say that the present invention is not limited to the embodiments described below, and can take various forms as long as it belongs to the technical scope of the present invention.

[First Embodiment] FIG. 1 is a circuit diagram showing a current detection circuit according to a first embodiment. As shown in FIG. 1, in the current detection circuit of the first embodiment, the drain is connected to the high potential side of the DC power supply (hereinafter referred to as power supply voltage VD1), and the source is connected to the low potential of the DC power supply via an electric load L. Channel M connected to the side (hereinafter referred to as ground potential)
An output transistor 1 composed of an OS transistor and an N-channel MO having the same type and the same polarity as the output transistor 1
The transistor includes an S transistor, and a current detection transistor 2 formed so as to have a different transistor size (that is, a geometric dimension) from the output transistor 1 by the same process as the output transistor 1.

Further, the current detecting circuit according to the first embodiment includes a driving circuit 3 for driving the output transistor 1.
A driving circuit 4 for driving the current detecting transistor 2, a current path forming element whose collector is connected to its own base and the drain of the current detecting transistor 2, and a PNP transistor 5 a as a first transistor
And the base and the emitter are respectively connected to the base and the emitter of the PNP transistor 5a.
a, a PNP transistor 5b as a second transistor constituting the current mirror circuit 5, the emitters of both PNP transistors 5a, 5b, and the output transistor 1
Connected to the drain and source of the current detecting transistor 2 and the drain and source of the current detecting transistor 2, and the same potential difference as the drain-source voltage (that is, the potential difference between the drain and the source) of the output transistor 1 And a voltage control circuit 6 generated between the drain and the source.

Here, the driving circuit 3 includes a constant current source 3a,
The cathode is downstream of the constant current source 3a and the output transistor 1
And the anode is connected to the output transistor 1
And a Zener diode 3b connected to the source of the power supply. Similarly, the drive circuit 4 includes a constant current source 4
and a Zener diode 4b having a cathode connected to the downstream side of the constant current source 4a and the gate of the current detection transistor 2, and an anode connected to the source of the current detection transistor 2.

The constant current flowing from the constant current source 3a of the drive circuit 3 and the constant current flowing from the constant current source 4a of the drive circuit 4 are set to the same value.
The Zener voltage of the Zener diode 3b and the Zener voltage of the Zener diode 4b of the drive circuit 4 are set to the same value.

Next, the voltage control circuit 6 includes a first resistor R1 having one end connected to the drain on the higher potential side of the drain and the source of the output transistor 1, and a drain and a source of the current detection transistor 2. One end is connected to the source on the low potential side, and the other end is connected to the first resistor R1.
A second resistor R2 connected to an end of the output transistor 1 on the opposite side, a third resistor R3 connected to one of the drain and the source of the output transistor 1 on the lower potential side, and One end is connected to the drain on the high potential side of the drain and the source of the current detecting transistor 2, and the other end is connected to the output transistor 1 of the third resistor R3.
A fourth resistor R4 connected to the end opposite to
A non-inverting input terminal (+ terminal) is connected to a connection point between the resistor R1 and the second resistor R2, and an inverting input terminal (-terminal) is connected to a connection point between the third resistor R3 and the fourth resistor R4. Connected
It comprises an operational amplifier OP whose output terminal is connected to the emitters of the PNP transistors 5a and 5b.

In the voltage control circuit 6, the output terminal of the operational amplifier OP is connected to the PNP transistors 5a, 5b
And the other end of the first resistor R1 opposite to the second resistor R2 becomes the input terminal J2 connected to the drain of the output transistor 1, and the third resistor R3 Of the fourth resistor R4 is the input terminal J3 connected to the source of the output transistor 1, and the end of the fourth resistor R4 opposite to the third resistor R3 is the current terminal J3. The input terminal J4 is connected to the drain of the detection transistor 2, and the end of the second resistor R2 opposite to the first resistor R1 is connected to the input terminal J5 connected to the source of the current detection transistor 2. Has become.

In the first embodiment, the resistances of the resistors R1, R2, R3, and R4 are all set to the same value. On the other hand, in the current detection circuit of the first embodiment, the drain of the output transistor 1 is connected to the power supply voltage VD1 via the terminal 20, and the source of the output transistor 1 is connected to the electric load L via the terminal 22. It is connected to the opposite side from the ground potential.

The source of the current detecting transistor 2 is connected to a low potential terminal 24. The low potential terminal 24 is lower than the power supply voltage of the constant current sources 3a and 4a and the operational amplifier OP It is connected to a potential equal to the lowest voltage that can be output (ground potential in the first embodiment).

In the current detection circuit of the first embodiment, the collector of the PNP transistor 5b is connected to the current detection terminal 26, and the current I3 flowing out of the current detection terminal 26 causes the drain of the output transistor 1 to be connected. The current I1 flowing between the sources (that is, the load current flowing through the electric load L, which is the drain current of the output transistor 1) is detected.

Next, the operation of the current detection circuit configured as described above will be described. First, in the drive circuit 3, a constant current from the constant current source 3a flows through the Zener diode 3b, so that a Zener voltage is generated between the cathode and the anode of the Zener diode 3b, and the Zener voltage is applied between the gate and the source of the output transistor 1. Is applied as a drive voltage to turn on the output transistor 1. Similarly, in the drive circuit 4, a constant current from the constant current source 4a flows through the Zener diode 4b, thereby generating a Zener voltage between the cathode and the anode of the Zener diode 4b. A drive voltage is applied between the gate and the source to turn on the current detection transistor 2.

As described above, since the Zener voltage of the Zener diode 4b is set to the same value as the Zener voltage of the Zener diode 3b, the voltage between the gate and the source of the output transistor 1 and the current detection transistor 2 The same drive voltage is applied between the gate and the source.

As described above, when the output transistor 1 and the current detecting transistor 2 are turned on, the power supply voltage VD
1 through the output transistor 1 (drain → source), a load current I1 flows to the electric load L. At this time, since the output transistor 1 has an ON resistance, a potential difference occurs between the drain and the source of the output transistor 1.

Then, the voltage control circuit 6 (specifically, the operational amplifier OP) is connected to the drain of the current detecting transistor 2.
The PNP transistor 5 is set so that the source-to-source voltage becomes the same as the drain-source voltage of the output transistor 1.
a, 5a.

Specifically, the drain voltage of the output transistor 1 and the source voltage of the current detecting transistor 2 are:
The voltage is divided by the first resistor R1 and the second resistor, and
The source voltage of the output transistor 1 and the drain voltage of the current detection transistor 2 are divided by the third resistor R3 and the fourth resistor R4.

Then, the operational amplifier OP divides the voltage of its own output terminal (that is, the emitter voltage of the PNP transistors 5a and 5b) by the voltage divided by the first resistor R1 and the second resistor R2 and the third voltage. Resistor R3 and fourth resistor R4
, So as to match the divided voltage.

Here, the first resistor R1 and the second resistor R2
If the ratio of the resistance value (R2 / R1) of the third resistor R3 to the resistance value of the third resistor R4 (R4 / R3) is the same, The voltage at the output terminal of the operational amplifier OP changes so that the source-to-source voltage becomes (R2 / R1 = R4 / R3) times the drain-source voltage of the output transistor 1. In the present embodiment, as described above, each resistor R
Since the resistance values of R1, R2, R3, and R4 are all set to the same value, the voltage between the drain and source of the PNP transistors 5a and 5a It is adjusted so as to be one time the source-to-source voltage.

By the operation of such a voltage control circuit 6,
When the voltage between the drain and the source of the current detecting transistor 2 is controlled to be equal to the voltage between the drain and the source of the output transistor 1, the potential differences between the terminals of the transistors 1 and 2 are all equal, and , 2 have the same operating point in all the saturated / non-saturated operating regions. Therefore, the current detecting transistor 2 (drain → source) is connected from the output terminal of the operational amplifier OP of the voltage control circuit 6 to the PNP transistor. 5a, the ratio of the transistor size between the current detecting transistor 2 and the output transistor 1 to the current I1 flowing through the output transistor 1 (ie, the load current flowing through the electric load L) (ie, the area of the geometric dimension) The current I2 according to the ratio) flows accurately.

Then, a PNP transistor 5b constituting the current mirror circuit 5 together with the PNP transistor 5a
, A current I3 proportional to the current I2 flowing through the PNP transistor 5a (ie, the current flowing through the current detecting transistor 2) flows. And the current I3
Flows from the current detection terminal 26 to the outside of the current detection circuit. By monitoring the current I3, the current I1 flowing between the drain and the source of the output transistor 1 is detected.

The ratio between the current I2 flowing through the PNP transistor 5a and the current I3 flowing through the PNP transistor 5b is the current mirror ratio of the current mirror circuit 5 determined by the transistor sizes of the two transistors 5a and 5b. In the current detection circuit of the first embodiment, assuming that the transistor size ratio between the output transistor 1 and the current detection transistor 2 is m: 1, the current I1 flowing through the output transistor 1 and the current flowing through the current detection transistor 2 are determined. The relationship with the current I2 is as shown in the following equation 1.

[0051]

I 2 = I 1 / m (Equation 1) Further, the current mirror ratio of the current mirror circuit 5 is represented by n:
If 1 (= 1 / n times), the current I3 flowing out of the current detection terminal 26 via the PNP transistor 5b is expressed by the following equation (2).

[0052]

I3 = I2 / n (Equation 2) Accordingly, from the above equations 1 and 2, the current I3 flowing out of the current detection terminal 26 is expressed as the following equation 3.

[0053]

I 3 = I 1 / (m × n) (Equation 3) As can be seen from Equation 3, the current I 3 is proportional to the current I 1 flowing through the output transistor 1, and the proportional constant is equal to that of the output transistor 1. It can be seen that it depends only on the transistor size ratio m of the current detection transistor 2 and the current mirror ratio n of the current mirror circuit 5, and has no relation to other conditions.

In the current mirror circuit 5, PN
The temperature characteristics of the P transistors 5a and 5b cancel each other, and the temperature characteristics of the output transistor 1 and the current detecting transistor 2 also cancel each other. Holds.

Therefore, according to the current detection circuit of the first embodiment, the current I1 flowing through the output transistor 1 can be detected with extremely high accuracy. In particular, in the current detection circuit of the first embodiment, the output transistor 1 and the current detection transistor 2 are not directly connected, and the drain or source voltage of the current detection transistor 2 is controlled. Instead, the voltage control circuit 6 controls the drain-source voltage of the current detection transistor 2 in accordance with the drain-source voltage of the output transistor 1.

For this reason, when a voltage fluctuation of the same phase occurs between the drain and the source of the output transistor 1, that is, the drain-source voltage of the output transistor 1 changes but the drain-source voltage does not change. In this case, the voltage control circuit 6 does not substantially operate, and the drain-source voltage of the current detection transistor 2 does not change.

Therefore, when a configuration similar to the above-described conventional circuit is employed, when a steep in-phase voltage fluctuation occurs at the drain and source of the output transistor 1 due to noise or the like, the voltage between the drain and source of the output transistor 1 becomes large. Although the voltage between the drain and the source of the current detecting transistor 2 changes even though the current does not change, the current detecting circuit according to the first embodiment causes such a problem. It is possible to eliminate the drawbacks of the conventional circuit and to stably perform high-precision current detection without being affected by noise.

In the first embodiment, the drive circuit 3 corresponds to a first drive circuit, and the drive circuit 4 corresponds to a second drive circuit. [Second Embodiment] FIG. 2 is a circuit diagram showing a current detection circuit according to a second embodiment.

As shown in FIG. 2, the current detection circuit of the second embodiment differs from the current detection circuit of the first embodiment shown in FIG. 1 only in the following four points (1) to (4). Are different. (1) First, the drain of the current detection transistor 2 is
The high potential side terminal 25 is connected to a potential (the power supply voltage VD1 in the second embodiment) equal to the highest voltage that can be output by the operational amplifier OP.

(2) Next, a current mirror circuit 7 is provided instead of the current mirror circuit 5, and the current mirror circuit 7 has a collector connected to its own base and the source of the current detecting transistor 2. And an NPN transistor 7a as a second transistor having a base and an emitter respectively connected to the base and the emitter of the NPN transistor 7a. I have.

Then, both NPN transistors 7a, 7b
Of the operational amplifier O constituting the voltage control circuit 6
It is connected to the output terminal of P. (3) In the voltage control circuit 6, the first resistor R1
A connection point between the third resistor R3 and the fourth resistor R2 is connected to the inverting input terminal (−terminal) of the operational amplifier OP.
The connection point with the resistor R4 is connected to the non-inverting input terminal (+ terminal) of the operational amplifier OP.

(4) In the current detection circuit of the second embodiment, the collector of the NPN transistor 7b is connected to the current detection terminal 26, and the current flowing from the current detection terminal 26 to the collector of the NPN transistor 7b The current I1 flowing between the drain and the source of the output transistor 1 is detected by I3.

In the current detection circuit of the second embodiment configured as described above, the driving circuits 3 and 4 also
The output transistor 1 and the current detection transistor 2 are turned on, and a load current I1 flows from the power supply voltage VD1 to the electric load L via the output transistor 1.

Then, the voltage control circuit 6 adjusts the emitter voltages of the NPN transistors 7a and 7b so that the drain-source voltage of the current detecting transistor 2 becomes equal to the drain-source voltage of the output transistor 1. As a result, the current I2 corresponding to the current I1 flowing through the output transistor 1 accurately flows through the current detecting transistor 2, and further flows through the NPN transistor 7b constituting the current mirror circuit 7 and the current I2 flowing through the current detecting transistor 2. A proportional current I3 will flow.

Therefore, by monitoring the current I3 flowing from the current detection terminal 26 to the collector of the NPN transistor 7b, the current I1 flowing between the drain and the source of the output transistor 1 can be detected accurately. In the current detection circuit of the second embodiment, the output transistor 1 and the current detection transistor 2 are not directly connected, just like the current detection circuit of the first embodiment.
Since the voltage between the drain and the source of the current detecting transistor 2 is controlled by the voltage control circuit 6 according to the voltage between the drain and the source of the output transistor 1, a highly accurate current can be obtained without being affected by noise. Detection can be performed stably.

Third Embodiment FIG. 3 is a circuit diagram showing a current detection circuit according to a third embodiment. As shown in FIG. 3, in the current detection circuit of the third embodiment, the source of the output transistor 1 is connected to the ground potential via the terminal 22 as compared with the current detection circuit of the first embodiment shown in FIG. , And the drain of the output transistor 1 is connected via a terminal 20 to the opposite side of the power supply voltage VD1 of the electric load L. The rest of the configuration is exactly the same as the current detection circuit of the first embodiment.

That is, the current detection circuit of the first embodiment employs a so-called high-side configuration in which the output transistor 1 is disposed on the higher potential side than the electric load L.
The current detection circuit according to the embodiment employs a so-called low-side configuration in which the output transistor 1 is disposed on the lower potential side than the electric load L.

The current detection circuit according to the third embodiment operates in exactly the same manner as the current detection circuit according to the first embodiment, and achieves exactly the same effects as the current detection circuits according to the first and second embodiments. be able to. [Fourth Embodiment] FIG. 4 is a circuit diagram showing a current detection circuit according to a fourth embodiment.

As shown in FIG. 4, in the current detection circuit of the fourth embodiment, as compared with the current detection circuit of the second embodiment shown in FIG.
2, the drain of the output transistor 1 is connected via a terminal 20 to the opposite side of the power supply voltage VD1 of the electric load L. And
Other configurations are exactly the same as those of the current detection circuit of the second embodiment.

That is, the current detection circuit of the second embodiment
Although the high-side format similar to the current detection circuit of the first embodiment is employed, the current detection circuit of the fourth embodiment employs a low-side format similar to the current detection circuit of the third embodiment. Also, the current detection circuit of the fourth embodiment operates in exactly the same manner as the current detection circuit of the second embodiment, and obtains exactly the same effects as the current detection circuits of the first to third embodiments. Can be.

[Others] In the current detection circuit of each of the above-described embodiments, an N-channel MOS transistor is used as the output transistor 1 and the current detection transistor 2. However, a P-channel MOS transistor is used as the output transistor 1 and the current detection transistor. 2 may be used to form a circuit. In addition, both transistors 1 and 2
As bipolar transistors and MIS (Metal-Insu
lator-Semiconductor) A transistor may be used.

For example, as the two transistors 1 and 2, N
When an NPN transistor is used instead of a channel MOS transistor, in FIGS.
The collector may be used instead of the drain, the emitter may be used instead of the source, and the base may be used instead of the gate, for circuit connection. In this case, a driving current (base current) flows between the base and the emitter of the output transistor by the constant current source 3a of the driving circuit 3, and the constant current source 4a of the driving circuit 4 A drive current equivalent to the drive current of the output transistor flows between the base and the emitter of the transistor.

On the other hand, the current mirror circuits 5 and 7 in each of the above-described embodiments are also configured by using MOS transistors instead of bipolar transistors.
Alternatively, a current mirror circuit having another configuration can be used. Further, as for the drive circuits 3 and 4, other circuit configurations can be used as long as the gate-source voltages of the output transistor 1 and the current detection transistor 2 are substantially equal. On the other hand, in each of the above-described embodiments, the transistors 5a and 7a forming a part of the current mirror circuits 5 and 7 are used as the current path forming elements, but instead of providing the current mirror circuits 5 and 7, the current detection is performed. A resistor as a current path forming element is provided in series between the transistor 2 and the output terminal of the operational amplifier OP,
The current I1 flowing through the output transistor 1 may be detected by monitoring the potential difference between both ends of the resistor. That is, the current I2 flowing through the resistor and the current detecting transistor 2 can be determined from the potential difference generated between both ends of the resistor, and the current I1 of the output transistor 1 is detected based on the current I2.

Further, in each of the above-described embodiments, the drain-source voltage of the current detection transistor 2 is made equal to the drain-source voltage of the output transistor 1.
The ratio between the source-to-source voltage and the drain-to-source voltage of the output transistor 1 may be set to a value other than 1.

For example, a first resistor R1 and a second resistor R2
If the ratio (R2 / R1) of the resistance value of the third resistor R3 and the ratio (R4 / R3) of the resistance value of the third resistor R3 and the fourth resistor R4 are both set to 2, the current detection The voltage between the drain and source of the transistor 2 is
The operational amplifier O is set to be twice the source-to-source voltage.
The voltage at the output terminal of P will change. Such a multiple value may be appropriately set according to the characteristics of the output transistor 1 and the current detection transistor 2.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a current detection circuit according to a first embodiment.

FIG. 2 is a circuit diagram illustrating a current detection circuit according to a second embodiment.

FIG. 3 is a circuit diagram illustrating a current detection circuit according to a third embodiment.

FIG. 4 is a circuit diagram illustrating a current detection circuit according to a fourth embodiment.

FIG. 5 is a circuit diagram illustrating a conventional current detection circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Output transistor L ... Electric load 2 ... Current detection transistor 3, 4 ... Drive circuit 3a, 4a ... Constant current source 3b, 4b ... Zener diode 5, 7 ... Current mirror circuit 5a, 5b ... PNP transistor 7a, 7b ... NP
N transistor 6 Voltage control circuit OP Operational amplifier R1 First
Resistor R2 ... Second resistor R3 ... Third resistor R4 ... Fourth
Resistor 24 ... Low potential side terminal 25 ... High potential side terminal 26 ...
Current detection terminal

Claims (7)

[Claims] 1. An output transistor having two output terminals connected in series in a current path for flowing a current to an electric load, the output transistor being of the same type and the same polarity as the output transistor, and being directly connected to the output transistor. A current detection transistor in which one of two output terminals is connected to a predetermined potential, and one terminal is connected to an output terminal of the current detection transistor opposite to the predetermined potential. Connected to the current path forming element, a terminal of the current path forming element opposite to the current detecting transistor, both output terminals of the output transistor, and both output terminals of the current detecting transistor. At the same time, the potential difference between both output terminals of the current detection transistor becomes a predetermined multiple of the potential difference between both output terminals of the output transistor. A voltage control circuit for changing a potential of a terminal of the current path forming element opposite to the current detection transistor, wherein a current flowing between both output terminals of the output transistor is detected by the current detection. A current detection circuit configured to detect the current based on a current flowing through the current path forming element via the current transistor. 2. The current detection circuit according to claim 1, wherein the voltage control circuit includes a voltage of a high-potential output terminal among both output terminals of the output transistor and both output terminals of the current detection transistor. A first resistor and a second resistor that divide the voltage of the output terminal on the low potential side, and the voltage of the output terminal on the low potential side of both output terminals of the output transistor and the transistor for current detection A third resistor and a fourth resistor that divide the voltage of the output terminal on the high potential side of the two output terminals; and a voltage divided by the first resistor and the second resistor and the third resistor. An operational amplifier that changes the potential of a terminal of the current path forming element opposite to the current detection transistor so that the voltage divided by the resistor and the fourth resistor match. Is characterized by Current detection circuit that. 3. The current detection circuit according to claim 1, wherein the output transistor and the current detection transistor are MOS transistors. 4. The current detection circuit according to claim 3, wherein: a first drive circuit for applying a drive voltage between a gate and a source of the output transistor; and a gate and a source of the current detection transistor. A second drive circuit for applying a drive voltage equivalent to the drive voltage therebetween. 5. The current detection circuit according to claim 1, wherein the output transistor and the current detection transistor are bipolar transistors. 6. The current detection circuit according to claim 5, wherein a first drive circuit that supplies a drive current between a base and an emitter of the output transistor, and a base and an emitter of the current detection transistor. And a second drive circuit for supplying a drive current equivalent to the drive current. 7. The current detection circuit according to claim 1, wherein the current path forming element has one output terminal connected to a side opposite to the predetermined potential of the current detection transistor. An output terminal connected to the output terminal and the other output terminal being a transistor connected to the voltage control circuit, the first transistor forming a part of a current mirror circuit; A current detection circuit, comprising the current mirror circuit together with the transistor of (1), and a second transistor for flowing a current proportional to a current flowing to the first transistor.