JPS6040963A - Electric current detecting circuit - Google Patents

Abstract

PURPOSE:To obtain a detected current output from a collector, by connecting a base of transistor for current detection with the input terminal and the first current input terminal of a current mirror circuit and connecting an emitter with the output terminal and the second current input terminal of the current mirror circuit. CONSTITUTION:A current mirror circuit 1 and transistor (TR) 4 for current detection are installed. The input terminal of the circuit 1 is connected directly or through a current dropping means with a base of the TR4 and the first current input terminal 2. The output terminal of the circuit 1 is connected with an emitter of the TR4 and the second current input terminal 3. A collector of the TR4 is connected with an output terminal 6. Thus, at the ferminal 6, when a current flowing through the terminal 3 is higher than that flowing through the terminal 3, a different current can be derived.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current detection circuit capable of detecting a difference current between two input currents.

A conventional detection circuit for detecting a difference current between a first input current and a second input current has a configuration as shown in FIG. The input of the current mirror circuit 1 is connected to a first current input terminal 2. Also, the output of the current mirror circuit 1 is the second
It is connected to the current input terminal 3 of the current detecting transistor 4 and also to the emitter of the current detecting transistor 4. Further, the base of the current detection transistor 4 is connected to a bias voltage source 5, and the collector of the current detection transistor 4 is connected to an output terminal 6.
connected to.

With this configuration, the first input current flowing to the first current input terminal flows to the input terminal of the current mirror circuit 1, and the output terminal of the current mirror circuit l receives the second current. Since it is connected to the input terminal 3 and the emitter of the current detection transistor 4, when the second input current flowing to the second current input terminal 3 is larger than the first input current, the second input current flowing to the second current input terminal 3 is larger than the first input current. ``One current flows through the current detection transistor 4'' and the difference current is taken out from the output terminal 6 connected to the collector of the current detection transistor 4.Here, the bias power supply 5 is connected to the current detection transistor 4. 4. Also, the first input current flowing to the first current input terminal 2 is smaller than the second input current flowing to the second current input terminal 3. If it is large, the current detection transistor 4 is cut off and no current flows through the multiple outputs.

As explained above, the second input current flowing to the second current input terminal 3 by the conventional current detection circuit shown in FIG. 1 is larger than the first input current flowing to the first current input terminal 2. In this case, it was possible to extract the difference current between the two.

However, as shown in FIG. 1, the conventional current detection circuit has the disadvantage that a bias power supply 5 is required.

An object of the present invention is to obtain a current detection circuit that does not require a bias power supply.

According to the present invention, there is provided a current mirror circuit which receives first and second currents at its input and output, respectively, a transistor having a pace connected to its input and an l emitter connected to its output; A current detection circuit having a differential current detection terminal connected to a collector is obtained.

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 shows a current detection circuit according to an embodiment of the present invention. Compared to the conventional example shown in FIG. is connected to current input terminal 2 of.

According to the current detection circuit shown in FIG. 2, since the first current input terminal 2 is connected to the input terminal of the current mirror circuit 1, the first current input terminal 2 flows to the first lightning input terminal 2. Equal currents are drawn from the output terminals of the current mirror circuit.

In this case, when the second input current flowing to the second current input terminal 3 is larger than the first input current, a current corresponding to the reciprocating current of both flows to the current detection transistor 4, and the current detection transistor 4 The differential current is taken out through the output terminal 6 connected to the collector of the . Here, since the base of the current detection transistor 4 is also connected to the input terminal of the current mirror circuit 1, the base bias current of the current detection transistor 4 also flows to the input terminal of the current mirror circuit 1. This results in an error in the detected differential current, but this usually does not pose a problem if hFE of the current detection transistor 4 is selected to be about 100 or more. If particularly high-precision operation is required, the current detection transistor 4 may be replaced with two or more Darlington-connected transistors.

Further, if the first input current flowing to the first current input terminal 2 is larger than the second input current flowing to the second current input terminal 3, the current detection transistor 4 is cut off and multi-output is performed. No current flows through.

As the current mirror circuit 1, the base of the transistor
A device with a forward biased diode connected between the emitters can be used. At this time, the pace of the transistor becomes the input terminal and the collector becomes the output terminal.

As explained above, the second input current flowing to the second lightning input terminal 3 by the current detection circuit according to the present invention shown in FIG. 2 is higher than the first input current flowing to the first current input terminal 2. When the current is larger, the difference current between the two can be taken out, and there is an advantage that a bias power supply is not required.

FIG. 3 shows a current detection circuit according to another embodiment of the present invention. The example shown in FIG. 3 differs from the example shown in FIG. A diode 7 is connected between the mirror circuit 10 input terminal and a diode 8 between the first current input terminal 2 and the second current input terminal 3.

According to the current detection circuit shown in FIG. 3, when the first input current flowing to the first current input terminal 2 is larger than the second input current flowing to the second input terminal 3, teeth,
The diode 8 is reverse biased and the first current input terminal 2
The first input current that flows through the diode 7 flows to the input terminal of the current mirror circuit 1. Since a current equal to the first input current is taken out from the output terminal of the current mirror circuit 1, the current detection transistor 4
A difference current between the first input current and the second input current flows through the output terminal 6, and the difference current is extracted from the output terminal 6 connected to the collector of the current detection transistor 4.

Here, the diode 7 operates as a voltage drop circuit for keeping the operating point of the output terminal of the current mirror circuit 1 within a range in which the current mirror circuit 1 operates normally.

On the other hand, the second input current flowing to the second current input terminal 3
is the first input current K1 flowing to the first current input terminal 2.
1, when the current I3 is large, the current I3 flows through the diode 8, the current detection transistor 4 is cut off, and no current flows through the output terminal 6.

Here Is”(I, -11)/2 ・・・−・・・−
...(1).

That is, since the current Il+I3, which is the sum of the first input current ■l and the current KIs flowing through the diode 8, flows through the input terminal of the current mirror circuit 1, a current CI++I3) also flows through the output terminal of the current mirror circuit 1. The sum of the current and the current I3 flowing through the diode 8 is the second input current I
2 and the circuit is balanced.

That is, (L+Is) +l3=(11+(I2 I
t)/2)+(I2-11)/2 ・・・−・・・・・・・・・・(2) =I2・・・・・・・・・・・・(3) In this way, diode 8 It works to maintain the balance of the circuit.

As explained above, the current detection circuit according to the present invention shown in FIG. When the current is larger, the difference current between the two can be taken out, and there is an advantage that a bias power supply is not required.

The collapse of the drawing, the entrustment eq FIG. 1 is a block diagram showing a conventional current detection circuit.

FIG. 2 is a block diagram showing one embodiment of the present invention. FIG. 3 is a block diagram showing another embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1... Current mirror circuit, 2... First current input terminal, 3... Second current input terminal, 4... Current detection transistor , 5...
・・Bias power supply, 6−・・・・Output terminal, 7, 8・
·····diode.

Mine map Figure 2 Mine 3 diagram

Claims (1)

[Claims] The input terminal of the current mirror circuit is connected to the base of the current detection transistor and the first current input terminal either directly or via a voltage drop means. A current detection circuit characterized in that an output terminal of the mirror circuit is connected to an emitter of the current detection transistor and a second current input terminal, and outputs multiple output currents from the collector of the current detection transistor.