JPH02311770A - Current detecting circuit - Google Patents

Abstract

PURPOSE:To obtain the output voltage proportional only to the current of a detection point by connecting a transistor and an output current detecting resistor between one input of a differential amplifier and the earth. CONSTITUTION:A current (i) flows to load 2 from a power supply 1 through the input current detecting resistor 4 of a current detecting circuit 3. The resistance value (r) of said resistor 4 is the detection resistance of the current (i) and a voltage value ir appears at both terminals of the resistor 4. The voltages at both terminals of the resistor 4 are inputted to a differential amplifier 5 through branch resistors 6, 7 and the potential difference between them is detected to control the base potential of a transistor 8 connected to an output side. During a period when input potential difference is detected, the emitter and collector of the transistor 8 are brought to a continuity state and the current proportional to a load current flows to the output current detecting resistor 9 connected between the transistor 8 and the earth. Therefore, by detecting said current, the voltage proportional to the input current can be detected. When the load 2 is not connected, the transistor 8 does not become a continuity state.

Description

[Detailed Description of the Invention] [Summary] Regarding a current detection circuit for a power line, the purpose is to remove offset voltage that occurs from the current detection circuit when there is no load, and the purpose is to remove offset voltage that occurs from the current detection circuit when there is no load. In a circuit that detects current, an input current detection resistor is inserted at the detection point, both ends of the detection resistor are connected to the input terminal of a differential amplifier via branch resistors, and one input of the differential amplifier is connected to the input terminal of the differential amplifier. A transistor and an output current detection resistor are connected between the ground, the base terminal of the transistor is connected through a feedback resistor or directly to the output terminal of the differential amplifier, and an output current detection resistor is connected between the transistor and the ground. The configuration is such that the voltage across both ends of the output is output.

[Industrial application field]

The present invention relates to load sharing in a power supply circuit and current detection in a power supply line.

When a plurality of power supply circuits supply current to the same load, the outputs of the power supply circuits are connected to each other and supplied to the load side, and the other end of the power supply circuit is connected to ground. In such a case, in order to know the current being supplied to the load from each power supply circuit, a current detection circuit is inserted into the non-ground terminal of each power supply circuit to detect the load current.

[Conventional technology]

FIG. 4 shows a circuit configuration diagram of a conventional power line current detection circuit. In the figure, 11 is a power supply circuit, 12 is a load, 1
3 is a current detection circuit, 14 is a detection resistor r, 15 is a differential amplifier AMP, 16 is a resistor R1 connected between the power supply side of the detection resistor and the input terminal of the amplifier, and II is a resistor connected between the load side of the detection resistor and the input terminal of the amplifier. The resistor R2, 18 connected between one input terminal represents a resistor R3 that provides feedback connection between the output terminal of the amplifier and one input terminal. ■ is the connection terminal with the power supply side,
■ is the connection terminal with the load side, and ■ is the output terminal of the current detection circuit.

Now, if the current flowing through the detection resistor r is i, and the voltage sent to the output terminal ■ is V, then the load current i is taken out as a detection voltage across the detection resistor r, and the differential amplifier 15 is connected to the resistors R1 and R2. is input to the output terminal ■ and the output voltage V
is sent. This voltage V allows the load current to be detected.

Figure 5 shows a characteristic diagram of load current and output voltage.

In the figure, if E is the voltage at no load, that is, the power supply voltage at offset, the relationship between the load current i and the output voltage V has a characteristic shown by a slope. The potential at the detection point ■ appears as an offset voltage at the output V, and the voltage ir detected across the detection resistor r by the load current i is added to the voltage amplified by the resistance ratio R3/R2 of the differential amplifier 15. An output V is sent out. Since the amplified voltage of ir is proportional to the current i, v=E+ (amplified voltage of ir), and the output voltage is detected with a constant slope characteristic. However, there is a problem in that when the potential E at the detection point (2) changes, the detected output voltage V changes even if the current i is constant.

[Problem to be solved by the invention]

In conventional current detection circuits, the output voltage increases in proportion to the load current, but since the offset voltage is constantly added, when the offset voltage fluctuates, the output voltage also fluctuates, and the difference between the load current and output voltage increases. The relationship is not constant (and the accuracy of the current detection circuit is impaired).

An object of the present invention is to remove this offset voltage from the current detection circuit and construct a circuit that obtains an output voltage proportional only to the detection point current.

[Means to solve the problem]

FIG. 1 shows the principle configuration diagram of the present invention. In the figure, 1 is a power supply, 2 is a load, 3 is a current detection circuit, 4 is an input current detection resistor, 5 is a differential amplifier, 6 and 7 are branch resistors, 8 is a transistor, 9 is an output current detection resistor, and 10 is a Indicates feedback resistance.

A power supply 1 is a DC power supply that supplies current to a load 2. The current detection circuit 3 is a circuit that detects the current flowing to the detection point ■, which is at a potential that fluctuates with respect to the ground potential.The input current detection resistor 4 extracts the current flowing to the detection point
inputs the voltage generated across the input current detection resistor 4 through the branch resistors 6 and 7, and sends it to the base of the transistor 8 directly or through the feedback resistor 10; It is connected between one input and ground, and the output voltage is detected from both ends of the output current detection resistor 9.

[Effect]

The detection point ■ on the power line L has a potential higher than the ground by the power supply voltage E. A current i flows from the power supply 1 to the load 2 through the current detection circuit 3. The resistance r of the input current detection resistor 4 is the current i
IR voltage appears across the resistor 4. The voltage across resistor 4 is input to differential amplifier 5 through branch resistors 6 and 7. When load 2 is connected, the human power potential of branch resistor 60 is higher than the input potential of branch resistor 7,
When the load 2 is not connected, the input potential of the branch resistor 6 and the input potential of the branch resistor 7 are equal, so the difference between the human input potentials is detected by the differential amplifier 5 and connected to the output side of the amplifier 5. The base potential of transistor 8 is controlled. While the difference in input potential is being detected, the emitter and collector of the transistor 8 are electrically connected, and a current proportional to the load current flows through the output current detection resistor 9 connected between the transistor 8 and the ground. Therefore, by detecting the voltage across the detection resistor 9, a voltage proportional to the input current can be detected. When the load current stops flowing, the differential amplifier 5
No output is sent from the transistor 8, the base potential to the transistor 8 disappears, the transistor 8 is no longer conductive, and no output voltage is sent across the output current detection resistor 9. That is, the output voltage across the output current detection resistor 9 becomes balanced from 0, and a voltage proportional to the input detection voltage ir can be detected.

〔Example〕

A circuit configuration diagram of an embodiment of the present invention is shown in FIG.

Figure (a) shows the case where the inverting input terminal of the amplifier is connected to the transistor, and figure (b) shows the case where the non-inverting input terminal of the amplifier is connected to the transistor.

In the figure, 1 is the power supply E, 2 is the load, 3 is the current detection circuit, 4 is the input current detection resistor r, 5 is the differential amplifier A, 6 is the branch resistor R1, 7 is the branch resistor R2, 8 is the transistor Q
1.9 indicates that the output current detection resistor RO110 is the feedback resistor R3.

In the case of figure (a), resistor R1 is connected to one input terminal of amplifier A and also connected to the emitter of transistor Q1, resistor R2 is connected to ten input terminals of amplifier A, and the output terminal of amplifier A is connected to transistor Q1. Connect to the base of Further, the collector of transistor Q1 is connected to output current detection resistor RO.

In the case of Figure (b), the resistor R1 is connected to the input terminal of the amplifier A and also to the collector of the transistor Ql,
Resistor R2 is connected to one input terminal of amplifier A, and the output terminal of amplifier A is connected to the base of transistor Q1 via feedback resistor R3. Further, the emitter of the transistor OLD is connected to the output current detection resistor RO. In Figures (a) and (b), the power source E has a fluctuating potential with respect to the ground, and the potential E is sent from the power line L to the detection point ■, and a current i is applied to the load 2 via the input current detection resistor 4. supply. Resistor 4 takes out the input detection voltage ir at both ends, and branches resistors R1 and R2.
An input potential is supplied to the amplifier 5 through. The input potential of R1 is higher than the input potential of R2, and when no load is connected, the potentials of R1 and R2 are equal.

In figure (a), the voltage ir across the resistor 4 is the resistor R1
and R2, and since the inverting input potential is higher than the non-inverting input potential, the output potential of the amplifier 5 becomes low. Since the base of transistor Ql is connected to the output of amplifier A, transistor Q1 conducts until the inverting input of amplifier A equals the non-inverting input potential. A current approximately equal to the emitter current flows through the collector of transistor Q1. That is, the currents flowing through the resistors R1 and RO are approximately equal, and a voltage equivalent to the voltage drop across the input current detection resistor r appears in the resistor R1. As a result, RO across the resistance r
/R1 times the voltage appears on the output current detection resistor RO.

An example of application of the present invention is shown in FIG. In the figure, 21 is a power supply A, 22 is a power supply B, 23 is an A detector, 24 is a B detector, and 25 is a load.

When the load 25 is connected to detector A and detector B,
Load balance can be detected by detecting the load currents iA and iA of the power supplies A and B as usual, but the balance of the power supplies can also be detected with the load 25 removed. That is, when the power supply voltages are balanced, currents iA and i flow to the A detector and the B detector.

does not flow, but if there is an imbalance between power supplies A and 8, either current iA or i will flow, so power supply A
The balance between the power supplies A and B can be easily measured by adjusting the currents iA and i to zero.

(Effects of the Invention) According to the present invention, it is possible to detect a current flowing at a point at a potential that fluctuates with respect to the ground potential, regardless of the fluctuating potential. In addition, it is possible to easily adjust the balance of multiple power supplies without connecting a load.

[Brief explanation of the drawing]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is a circuit block diagram of an embodiment, Fig. 3 is a connection block diagram of an applied example, Fig. 4 is a circuit block diagram of a conventional example, and Fig. 5 is a conventional example. The current-voltage characteristic diagram is shown. In the figure, 1.11.21.22 is a power supply, 2, 12.
25 is a load, 3 and 13 are current detection circuits, 4 and 14 are input terminal detection resistors, 5.15 is a differential amplifier, and 6. 7.16
17 is a branch resistor, 8 is a transistor, 9 is an output current detection resistor, 10.18 is a feedback resistor, and 23.24 is a detector. Principle configuration diagram of the present invention Figure 1 (a) When the inverting input terminal of the amplifier is connected to a transistor (5) When the non-inverting input terminal of the amplifier is connected to the transistor Circuit configuration diagram of the embodiment Figure 2 Application example Connection configuration diagram Fig. 3 ■ 1) I2 Fig. 4 □ 1 Offset voltage □ Fig. 5

Claims (1)

[Claims] In a circuit (3) that detects a current flowing through a detection point at a potential that fluctuates with respect to ground potential, an input current detection resistor (4) is inserted at the detection point, and the detection resistor (4) A differential amplifier (5) is connected to both ends of the
), one input of the differential amplifier (5) and ground are connected via the transistor (8) and the output current detection resistor (9), and the base terminal of the transistor (8) is connected to the input terminal of the differential amplifier (5). It is connected through the feedback resistor (10) or directly to the output terminal of the differential amplifier (5), and outputs the voltage across the output current detection resistor (9) connected between the transistor (8) and the ground. Characteristic current detection circuit.