JP2862370B2 - Current detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention is used, for example, in a voltage applied current measuring device which applies a voltage to a load and measures a current flowing through the load at that time.
The present invention relates to a current detection circuit in which a current detection resistor is connected in series between an output terminal of an amplifier and one end of a load, and detects a current flowing to the load from a voltage between both ends of the current detection resistor.

[Prior Art] FIG. 6 shows a conventional current detection circuit. The inverting input terminal of the amplifier 11 is connected to the voltage source 13 through the input resistor 12,
The non-inverting input terminal of the amplifier 11 is grounded, the output terminal 14 is connected to one end of a load 16 through a current detection resistor 15, and a connection point 17 between the load 16 and the current detection resistor 15 is connected to a feedback resistor 18
Is connected to the inverting input terminal of the amplifier 11, and the other end of the load 16 is grounded. The output terminal 14 of the amplifier 11 is connected to a resistor 19−
The connection point 17 is grounded through a resistor 22-23, the connection point between the resistors 19 and 21 is connected to a non-inverting input terminal of an operational amplifier 24, and the connection point between the resistors 22 and 23 is an operational amplifier. The inverting input terminal is connected to an output terminal of an operational amplifier 24 via a feedback resistor 25, and the output terminal is connected to a current detection output terminal 26.
An operational amplifier 24 and resistors 19, 21, 22, 23 and 25 constitute a differential amplifier circuit 27.

The output voltage of the power supply 13 is E, and the resistance values of the resistors 12 and 18 are R ₁ ,
When R _2, the voltage V _l of the connection point 17, Becomes This voltage _Vl is applied to the load 16, at which time the load
The charge current _Il flowing through the current detection resistor 16 flows through the current detection resistor 15, and the voltage generated at the current detection resistor 15 is changed by the differential amplifier circuit 27.
And output to the output terminal 26. That is, a voltage corresponding to a difference voltage between the potential of the output terminal 14 of the amplifier 11 (the potential at one end of the current detection resistor 15) and the potential of the connection point 17 (the potential at the other end of the current detection resistor 15) is output terminal. Obtained on 26. The resistance values of resistors 19, 21, 22, 23, ₂₅ are represented by R ₃ , R ₄ , R ₅ , R ₆ ,
Assuming that R ₇ , the resistance value of the current detection resistor 15 is R _S , the voltage of the output terminal 14 is V ₀ , and the parallel resistance value of the resistors 23 and 25 is R ₆ // R ₇ , a current detection output terminal 26 is obtained. The output voltage _VIM is given by the following equation.

The resistors R ₃ , R ₄ , R ₅ , R ₆ and R ₇ are selected so that
Therefore, by measuring the voltage V _IM , the load current I _l becomes (V
_IM / R _S ) × (R ₅ / R ₇ ).

"Problems that the Invention is to Solve" (3) is satisfied, and the common-mode voltage rejection ratio of the operational amplifier 24 is not large, the detection voltage V _IM by the magnitude of the output voltage V ₀ which amplifier 11 varies, The load current _Il cannot be detected correctly. In particular, if the output voltage V ₀ is sufficiently large with respect to R _S · I _l , the state becomes the same as when the common mode voltage V ₀ is applied to the operational amplifier 24, and the error increases if the common mode voltage rejection ratio is not large. Further, when the output voltage V ₀ is large, (3) is not satisfied, this error becomes larger with the smaller value.

Accordingly, a high-precision and expensive resistor is required as the resistors 19, 21, 22, 23, and 25, and an expensive operational amplifier 24 having a large common-mode voltage rejection ratio is required.

According to the first aspect of the present invention, a current detection resistor is connected in series between the output terminal of the amplifier and one end of the load, and the current flowing through the load is detected by the current detection. In a current detection circuit for detecting a voltage between both ends of a resistor, one output terminal of a reference power supply is connected to a base via the current detection resistor, and the other output terminal of the reference power supply is connected to an emitter via a resistor. A current conversion circuit comprising a transistor connected to a collector to supply a first current of a current mirror circuit to a collector; and a power supply voltage having an absolute value higher than a voltage at one end of the load, and supplying the first current to a second current. The current mirror circuit for converting the second current into a voltage,
And a current-to-voltage conversion circuit for detecting a current flowing to the load from the voltage.

According to the invention of claim 2, a current detection resistor is connected in series between the output terminal of the amplifier and one end of the load, and a current flowing through the load is detected from a voltage between both ends of the current detection resistor. In the current detection circuit, one output terminal of the reference power supply is connected to the base via the current detection resistor, the other output terminal of the reference power supply is connected to the emitter via the first resistor, and a first current mirror is provided. A first current conversion circuit comprising a first transistor for supplying a first current of the circuit to a collector, one output terminal of the reference power supply is directly connected to a base, and the other output terminal of the reference power supply is connected to a second resistor; A second current conversion circuit comprising a second transistor connected to the emitter via the second current mirror circuit and supplied to the collector of the second current mirror circuit, and having a higher absolute value than the voltage at one end of the load. Power supply voltage is supplied, the first
A first current mirror circuit that converts a current into a second current, a second current mirror circuit that is supplied with a power supply voltage higher than a voltage at one end of the load, and converts the third current into a fourth current; A current-voltage conversion circuit for converting a difference between the second current and the fourth current into a voltage and detecting a current flowing to the load from the voltage.

According to the invention of claim 3, a current detection resistor is connected in series between the output terminal of the amplifier and one end of the load, and a current flowing through the load is detected from a voltage between both ends of the current detection resistor. In the current detection circuit, one output terminal of a reference power supply is connected to a base via the current detection resistor, and the other output terminal of the reference power supply is connected to an emitter via a resistor. A current conversion circuit including a transistor whose current is supplied to a collector, a power supply voltage having an absolute value higher than a voltage at one end of the load, and a current mirror circuit configured to convert the first current into a second current; A second current conversion circuit that converts the second current into a third current and negatively feeds back to the input side of the amplifier.

"Embodiment" FIG. 1 shows an embodiment of claim 1 in which parts corresponding to those in FIG. 6 are denoted by the same reference numerals. The voltage across the current sensing resistor 15 is converted by the current converter circuit 28 to the first current i ₁ in this embodiment. That is, one end of the current detection resistor 15 on the load side is connected to the base of the npn transistor 29, the emitter of the transistor 29 is connected to one end of the resistor 31,
One end of the current detection resistor 15 on the amplifier 11 side is connected to one end of the reference power supply 32, and the other end of the reference power supply 32 and the other end of the resistor 31 are connected to each other. The voltage applied to the resistor 31 is determined from the reference voltage V _R1 of the reference power supply 32, the voltage I _l · _RS generated by the current detection resistor 15, and the voltage V _BE1 between the base and the emitter of the transistor 29. the current flowing through the vessel 31 to flow as the collector current of the transistor 29, a first current i ₁ to the collector current is converted. The current conversion circuit 28 is converted into a linearly first current i ₁ the load current I _l.

The first current i ₁ is supplied to the current mirror circuit 33 by the second current i ₂
Is converted to That is, the power supply 34 is a diode 35-a resistor 36
The collector of the transistor 29 is connected to the collector of the transistor 29. The connection point of the collector and the resistor 36 is connected to the base of the pnp transistor 37. The emitter of the transistor 37 is connected to the power supply 34 through the resistor 38. The voltage V _{DD of the} power supply 34 is the connection point 1
7 load voltage is higher than the maximum value of V _l of the first current i ₁ is always to flow toward the emitter from the collector of the transistor 29. The voltage drop due to the first current i ₁ of the resistor 36, and the forward voltage of the diode 35, the base of the transistor 37, the voltage applied from the emitter voltage to the resistor 38 determines the current flowing through the resistor 38 There flows as the collector current of the transistor 37, the collector current becomes the second current i ₂ that has been converted. The current mirror circuit 33 is the first current
linearly converting the second current i ₂ to i _1.

The second current i ₂ is converted into a voltage by the current-voltage conversion circuit 39 and supplied to the current detection output terminal 26. That is, the collector of the transistor 37 is connected to the reference power supply 42 through the resistor 41 and to the non-inverting input terminal of the operational amplifier 43,
The inverting input terminal and the output terminal of the operational amplifier 43 are connected to each other. The reference power supply 42 is for subtracting a voltage corresponding to the converted current of the reference voltage V _R1 of the reference power supply 32. In this example, the positive side of the reference power supply 32 is connected to the current detection resistor 15, and the reference power supply 42 Is connected to the resistor 41,
The positive side of 42 is connected to a reference potential point (common potential point) for measurement, in this example a ground potential point. Resistor with second current i ₂
The voltage generated at 41 is obtained at the current detection output terminal 26.

Next, the operation of the current detection circuit will be described. Load current
_Assuming that I _l , the resistance value of the current detection resistor 15 is R _S , the reference voltage of the reference power supply 32 is V _R1 , the voltage between the base and the emitter of the transistor 29 is V _BE1 , and the resistance value of the resistor 31 is R ₈ , One current i ₁ is given by the following equation.

Assuming that the resistance values of the resistors 36 and 38 are R ₉ and R ₁₀ , the forward drop voltage of the diode 35 is V _D , and the voltage between the base and the emitter of the transistor 37 is V _BE2 , the second current i ₂ is given by the following equation. .

The resistance value of the resistor 41 is R ₁₁ and the reference voltage of the reference power supply 42 is V _R2
Then, the voltage _VIM obtained at the current detection output terminal 26 is expressed by the following equation.

When _{V IM = R 11 · i 2} -V R2 (6) (4) ~ (6) are summarized formula, the load current I _l and the output voltage
The relationship between the V _IM becomes the following equation.

Here, V _BE1 = V _BE2 = V _D = 0.6 (V), and V _R1 = V _R2 +
When 0.6 (V) and R ₈ = R ₉ = R ₁₀ = R ₁₁ are selected, V _IM = −R _S · I _l (8). Thus, the detection voltage _VIM is equal to the output voltage V of the amplifier 11.
_Be independent of ₀ . To affect the common-mode voltage rejection is only insulation resistance R _U with respect to the common potential point of the current conversion circuit 28, it is possible to measure with high accuracy. Note that V _BE1 = V _BE2 =
It is relatively easy to make V _D, and R ₈ = R ₉ = R ₁₀ = R ₁₁ is not affected by the output voltage V _D even if it is not made to be highly accurate. It is clear from

In FIG. 1, the current mirror circuit 33 is operated at a voltage higher than the maximum value of the load voltage _Vl.
33 may be operated at a voltage lower than the minimum value of the load voltage _Vl . An example is shown in FIG. 2 by attaching the same reference numerals to parts corresponding to FIG. In this example, a pnp transistor is used as the transistor 29 in the current conversion circuit 28, and the reference power supply 32
Is connected to the current detection resistor 15 side. In the current mirror circuit 33, an npn transistor is used as the transistor 37, and the negative side of the power supply 34 is a diode 35 and a resistor 38.
Connected to. In the current-voltage conversion circuit 39, the positive side of the reference power supply 42 is connected to the resistor 41 side.

In the above description, the current conversion circuit 28 and the current mirror circuit 33 are configured using junction transistors, but may be configured using FETs. An example is shown in FIG. That is, in the current conversion circuit 28, the output terminal 14 of the amplifier 11 is connected to the positive side of the reference power supply 32 and the non-inverting input terminal of the operational amplifier 44, and the resistor 45 is connected between the negative side of the reference power supply 32 and the connection point 17. −46 is connected, the connection point of the resistors 45 and 46 is connected to the inverting input terminal of the operational amplifier 44, the output terminal of the operational amplifier 44 is connected to the gate of the FET 47, and the source of the FET 47 is connected to the resistors 45 and 46. Connected to a connection point.

Assuming that the resistance values of the resistors 45 and 46 are R ₁₂ and R ₁₃ , the inverting input terminal and the non-inverting input terminal of the operational amplifier 44 have the same potential due to the feedback action, that is, the output voltage of the output terminal 14 of the amplifier 11.
The V _0. Therefore, the current i ₀₁ flowing through the resistor 45 is V _R1 / R ₁₂
Next, the difference between the load voltage V _l and the output voltage V ₀ which connection point 17, that is, the voltage across V _l -V ₀ = V _b of the current detection resistor 15 resistor
Applied to 46. Therefore, the current i _o2 flowing through the resistor 46 is V _b /
The R _13. Since the sum of the current i ₁ flowing through the FET 47 and the current i ₀₂ flowing through the resistor 46 flows through the resistor 45, i ₁ = i ₀₁ −i _o2 =
_{(V R1 / R 12) -} (V b / R 13) , and the voltage V _b generated in the current detecting resistor 15 is converted to a first current i _1.

In the current mirror circuit 33, the drain of the FET 47 is connected to the power supply 34 through the resistor 36 and the operational amplifier
48, the inverting input terminal of the operational amplifier 48 is connected to the power supply 34 through the resistor 58, the output terminal of the operational amplifier 48 is connected to the gate of the FET 49, and the source of the FET 49 is connected to the operational amplifier 48. Connected to inverting input terminal. First
A voltage generated in the resistor 36 by the current i _1, so that the voltage becomes equal occurring resistor 38 by the second current i ₂ flowing through the FET 49, a second current i ₂ flows, the first current i ₁ is the 2 current i ₂
Is converted to In this way, the voltages between the gates and the sources of the FETs 47 and 49 are compensated by the operational amplifiers 44 and 48, respectively, so that the current can be detected accurately.

FIG. 4 shows a second embodiment of the present invention. Parts corresponding to those in FIG. 1 are denoted by the same reference numerals. A power supply 51 is used instead of the reference power supply 32 in FIG. The output terminal 14 is connected to the base of the npn transistor 52, and the emitter of the transistor 52 is connected through the resistor 53 to the connection point between the resistor 31 and the power supply 51. Transistor 29, resistor 31, the voltage-current conversion circuit 54 which converts the load voltage V _l the connection point 17 to the current i ₁ by the power source 51 is configured, transistor 52, resistor 53, the output voltage of the output terminal 14 by power supply 51 voltage-current conversion circuit 55 for converting the V ₀ to the current i ₃ is formed. The current i ₁ is converted by the current mirror circuit 33 into a current i ₂ . The collector of transistor 52 is connected to power supply 34 through diode 56-resistor 57, and is connected to the base of pnp transistor 58, and the emitter of transistor 58 is connected to power supply 34 through resistor 59. Diode 56, resistors 57, 59, transistor 5
8, the power source 34, current mirror circuit 61 which converts the current i ₃ to the current i ₄ is formed.

The collector of the transistor 37 is connected to the inverting input terminal of the operational amplifier 62, the collector of the transistor 58 is connected to the non-inverting input terminal of the operational amplifier 62, and is grounded through the resistor 63. The output terminal is connected by a resistor 64. Operational amplifier 62, resistor
63 and 64 constitute a current-voltage conversion circuit 65, and a transistor 37
And outputs a voltage proportional to the difference between the current i ₄ than more current i ₂ and the transistor 58 to the current detection output terminal 26. In this way, a voltage corresponding to the voltage _RS · _Il generated at the current detection resistor 15 is obtained at the output terminal 26. In this case, the power supply 51 is commonly used as the voltage-to-current conversion circuits 54 and 55, and the conversion currents corresponding to the voltages are subtracted from each other by the current-voltage conversion circuit 65. There is no need for a device capable of obtaining a stable reference voltage.

FIG. 5 shows an embodiment of the third aspect of the present invention. In this example, as in FIG.
15 is converted into a first current i ₁ , and this first current i ₁
i ₁ but is converted to the second current i ₂ by the current mirror circuit 33, increasing in this embodiment the second current i ₂ is converted into a current i ₅ by a current converter 66 to the inverting input terminal of the amplifier 11 Returned and supplied. That is, the collector of transistor 37 is npn
Connected to the collector of transistor 67, transistor 67
Emitter is grounded through a resistor 68 and the base is
Connected to 69, the collector of the transistor 67 is connected to the inverting input terminal of the amplifier 11. The feedback resistor 18 in FIG. 1 is omitted.

The transistor 67 has a constant current i _{6 determined by} the voltage of the power supply 69.
Flow, current i ₅ of the difference between the current i ₂ of the current i ₆ and a current mirror circuit 33 is fed back to the inverting input terminal of amplifier 11 as an output of the current converter circuit 66. As a result, the current detection resistor 15
In such a manner that the voltage between both ends becomes constant. That is, this circuit can be used as a current generator.

In the example of FIG. 3 to FIG. 5, it may be configured to operate at a lower power than the minimum value of the respective load voltage V _l the current mirror circuit 33, 61 as in the example of FIG. 2. 2, 4, and 5, a current conversion circuit, a voltage-current conversion circuit, and a current mirror circuit are respectively shown.
You may comprise using FET.

[Effect of the Invention] As described above, according to the present invention, since the differential amplifier is not used, the resistors 19, 21, and
The 22, 23, 25 and of high precision, and the operational amplifier 24 there is no need assume is remarkably large common-mode voltage rejection ratio, regardless of the voltage caused by the load current to the current detection resistor to the output voltage V ₀ which amplifier Can be detected correctly.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the first aspect of the invention, FIGS. 2 and 3 are connection diagrams each showing a modified example thereof, and FIG. 4 is a connection diagram showing an embodiment of the second aspect of the invention. FIG. 5 is a connection diagram showing an embodiment of the third aspect of the invention, and FIG. 6 is a connection diagram showing a conventional current detection circuit.

Claims (3)

(57) [Claims] A current detecting circuit is connected in series between an output terminal of an amplifier and one end of a load, and detects a current flowing through the load from a voltage between both ends of the current detecting resistor. One output terminal of the reference power supply is connected to the base via the current detection resistor, the other output terminal of the reference power supply is connected to the emitter via the resistor, and the first current of the current mirror circuit is connected to the collector. A current conversion circuit including a transistor to be supplied; a power supply voltage having an absolute value higher than a voltage at one end of the load; a current mirror circuit configured to convert the first current into a second current; And a current-to-voltage conversion circuit that converts a voltage into a voltage and detects a current flowing to the load from the voltage. 2. A current detection circuit comprising: a current detection resistor connected in series between an output terminal of an amplifier and one end of a load; and a current flowing through the load is detected from a voltage between both ends of the current detection resistor. One output terminal of the reference power supply is connected to the base via the current detection resistor, and the other output terminal of the reference power supply is connected to the emitter via the first resistor; A first current conversion circuit comprising a first transistor for supplying a current to a collector, one output terminal of the reference power supply being directly connected to a base, and the other output terminal of the reference power supply being an emitter via a second resistor; A second current conversion circuit comprising a second transistor connected to the second current mirror circuit and supplying a third current of the second current mirror circuit to a collector; and a power supply voltage having an absolute value higher than a voltage at one end of the load. Is supplied, the and the first current mirror circuit for converting the first current to the second current, power supply voltage higher than the voltage of one end of the load is supplied,
A second current mirror circuit for converting the third current to a fourth current; and converting a difference between the second current and the fourth current into a voltage,
And a current-to-voltage conversion circuit for detecting a current flowing to the load from the voltage. 3. A current detection circuit comprising: a current detection resistor connected in series between an output terminal of an amplifier and one end of a load; and a current flowing through the load is detected from a voltage between both ends of the current detection resistor. One output terminal of the reference power supply is connected to the base via the current detection resistor, the other output terminal of the reference power supply is connected to the emitter via the resistor, and the first current of the current mirror circuit is connected to the collector. A current conversion circuit including a transistor to be supplied; a power supply voltage having an absolute value higher than a voltage at one end of the load; a current mirror circuit configured to convert the first current into a second current; And a second current conversion circuit that converts the current to a third current and negatively feeds back to the input side of the amplifier.