JP2002366236A - Current regulation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current regulation device which can control the level of output current and reduces a manufacturing cost by using only one current detection resistance that is highly accurate and expensive. SOLUTION: Voltage outputted by a scale factor switching circuit is used to correct a reference voltage, and proper current is outputted with the corrected voltage. Meanwhile, a current detection circuit converts the output current into voltage and outputs the converted voltage. The voltage outputted by the scale factor switching circuit fluctuates accordingly to the voltage outputted by the current detection circuit. In the case the output current fluctuates by disturbance, the voltage outputted by the scale factor switching circuit also varies to correct the reference voltage. Then, a current control circuit controls the output current level so as to cancel the fluctuation of inputted voltage, since the voltage inputted to the current control circuit corresponds to the fluctuation of the output current level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current device for supplying a stable current, and more particularly, to a constant current device capable of switching the current in an arbitrary range.

[0002]

2. Description of the Related Art A constant current device for switching an output current has been used for various devices. For example, it is used for an electric wire length measuring device that measures the length of an electric wire. In a wire measuring instrument,
A constant and stable current is passed through the wire, the voltage across the wire is measured, and the resistance is calculated from Ohm's law. And
The length of the electric wire is calculated using equation (1). Length (m) = resistance value (mΩ) × cross-sectional area (mm ² ) / specific resistance value (mm ² mΩ / m) (1)

[0003] Here, an electric wire having a large cross-sectional area has a very small resistance value. Therefore, if the current flowing through the electric wire for measurement (measurement current) is small, the generated voltage becomes weak.
For this reason, the influence of noise is large, and the measurement accuracy is deteriorated.
On the other hand, for wires with a small cross-sectional area, if the measured current is large,
The temperature rise of the electric wire due to self-heating becomes large, causing a measurement error. Therefore, in order to cope with various electric wires, it is necessary for the electric wire length measuring device to switch a current to flow depending on the thickness of the electric wire.

FIG. 9 shows a block diagram of a conventional constant current device. Constant current device 100 shown in FIG.
, The current control circuit 110 outputs a constant and stable output current 101 based on the voltage 105. On the other hand, as an input to the range changeover switch 120, a current 106 branched from a drawing point 102 of the output current 101 is input. The range changeover switch 120 is selected and set in advance according to the required output current 101.

The current 106 is input to a current detection resistor 130 selected and set by a range changeover switch 120. Then, the current 106 is converted into a voltage 107 by the current detection resistor 130, the reference voltage 102 is corrected at the addition point 103, and the corrected reference voltage 102 (voltage 105) is input to the current control circuit 110. In other words, it can be said that the range changeover switch 120 and the current detection resistor 130 are in series with the negative feedback loop of the current control circuit 110.

According to the constant current device 100, the output current 10
1 fluctuates due to disturbance, a voltage 107 corresponding to the fluctuation of the output current 101 is output from the current detection resistor 130, the reference voltage 104 is corrected, and the corrected voltage 105
Is input to the current control circuit 110, so that a constant and stable output current 101 can be obtained.

FIG. 10 shows a constant current circuit 100 'for realizing the constant current device 100 shown in the block diagram of FIG.
In FIG. 10, the range changeover switch 120 includes S ₁ ,
Formed by S ₂ , S ₃ , S _1A , S _2A , S _3A ,
Switches S ₁ , S ₂ , S ₃ are respectively S _1A , S _2A , S
It operates corresponding to _3A . Also, the current control circuit 110
Is formed by an operational amplifier 111 and an FET (field effect transistor) 112. Furthermore, the current detection resistor 130 is formed by the current detection resistors R ₁ , R ₂ , and R ₃ . The current detection resistors R ₁ , R ₂ , and R ₃ have different resistance values according to the output current I ₀ .

[0008] Operation of the constant current circuit 100 in FIG. 10, for example, result ON the switch _{S 1, S 1 A} also ON, the voltage is generated in the current detecting resistor R1. Voltage generated in the current detecting resistor R1 is input to the inverting input terminal of the operational amplifier 111 via a switch S _1. On the other hand, the reference voltage 104 is input to the non-inverting input terminal of the operational amplifier 111, the output of the operational amplifier 111 is input to the gate terminal of the FET 112,
Controlling the output current _{I 0} to the output of the ET112.

[0009] If the output current I ₀ is changed due to a disturbance or the like, also changes the current flowing through the current detection resistor R1, since thereby the input also changes to the inverting input terminal of the operational amplifier 111, input to the gate terminal of the FET112 Therefore, the output current I ₀ is corrected, so that the output current I ₀ is supplied stably and stably.

[0010]

SUMMARY OF THE INVENTION A conventional current detection circuit 1
00 ', the current detection resistor (R₁, R₂, R₃Switch)
Range switch (S_1A, S_2A, S_{3 A})of
To eliminate errors due to on-resistance, another pair of switches
Itch (S₁, S ₂, S₃) Is provided. Further
In addition, these switches (S₁, S₂, S₃, S_1A, S
_2A, S_3A) Is the minimum range switch
With a sufficiently low leakage current and a large current range.
The switch is required to have a sufficiently small on-resistance.
However, switches that fully satisfy these conditions are special
And therefore very expensive.

[0011] Furthermore, in order to stabilize the current output from the constant current circuit 100 'with high accuracy, necessary to set a current detection resistor _{(R 1, R 2, R} 3) good stability with high precision There is. The current detection resistors (R ₁ , R ₂ , R ₃ ) satisfying such conditions are also very expensive. Therefore, the conventional constant current circuit 100 '(constant current device 100) having a plurality of ranges is very expensive because many expensive switches and resistors are provided.

An object of the present invention is to provide a constant current device which has a plurality of ranges, is highly accurate, and has a low manufacturing cost.

[0013]

According to a first aspect of the present invention, there is provided a current control circuit formed so as to be capable of outputting an output current which is a constant current based on an input voltage, and converting the output current into a voltage. A current detection circuit formed so as to be able to output the voltage, and a magnification switching circuit which forms the output voltage so as to be switchable, and wherein the output voltage fluctuates according to the voltage output by the current detection circuit. Wherein the voltage input to the current control circuit is formed by correcting the reference voltage by the voltage output from the magnification switching circuit.

According to the first aspect of the invention, the voltage output from the magnification switching circuit corrects the reference voltage, and the corrected voltage outputs an output current. On the other hand, the current detection circuit converts the output current into a voltage and outputs the converted voltage. The voltage output from the magnification switching circuit fluctuates according to the voltage output from the current detection circuit. Here, when the output current fluctuates due to disturbance, the voltage output from the magnification switching circuit also fluctuates to correct the reference voltage. Then, since the voltage input to the current control circuit also corresponds to the fluctuation of the output current, the current control circuit controls the output current to be constant based on the fluctuation of the input voltage. That is, even when the output current fluctuates due to disturbance, a constant output current can be stably output.

Furthermore, since the magnification switching circuit is formed so as to be able to switch the output voltage, the output current can be switched to various current values. In the conventional constant current device, the current value of the output current is switched by switching a high-precision and expensive current detection resistor. However, according to the present invention, the switching of the current value of the output current can be switched by the magnification switching circuit. Therefore, it is sufficient to provide one high-precision and expensive current detection resistor in the current detection circuit. Further, it is not necessary to use switches in consideration of on-resistance and leakage current. therefore,
According to the first aspect of the present invention, it is possible to manufacture a constant current circuit that can switch to various currents at a lower cost than in the past.

According to a second aspect of the present invention, a current control circuit is formed so as to be capable of outputting an output current which is a constant current based on an input voltage, and is capable of converting an input current into a voltage and outputting the voltage. A current detection circuit, and a current switching circuit that forms the output current in a switchable manner, wherein the output current varies in accordance with the voltage output by the current detection circuit. The current input to the current detection circuit is formed by correcting the output current by the current output from the magnification switching circuit, and the voltage input to the current control circuit is a voltage output by the current detection circuit. Are formed by correcting the reference voltage.

According to the second aspect of the present invention, the voltage output from the current detection circuit is input to the magnification switching circuit, and the magnification switching circuit outputs a current corresponding to the input voltage. on the other hand,
The current obtained by correcting the output current with the current output from the magnification switching circuit is input to the current detection circuit. Then, the current detection circuit converts the input current into a voltage and outputs the voltage. The output voltage is input to the magnification switching circuit and used for correcting the reference voltage. The corrected (reference) voltage is input to the current control circuit, and a stable and constant current is output based on the corrected (reference) voltage.

According to the second aspect of the present invention, since the switching of the output current is performed by the magnification switching circuit, only one current detecting resistor is required as in the first aspect, and the switch does not need to be high precision. Further, according to the invention of claim 2, the voltage output from the current detection circuit directly corrects the reference voltage.
That is, the number of control elements for keeping the output current constant is reduced, so that errors and the like generated from the circuit can be reduced. Therefore, the output current is controlled to be more accurate and constant.

[0019]

FIG. 1 is a block diagram of a constant current device 1 according to an embodiment of the present invention. The current control circuit 2 controls the output current 4 based on the input voltage 3 so that the output current 4 can be constantly output. The current detection circuit 5 converts the output current 4 branched from the extraction point 6 into a voltage 7 and outputs it. The voltage 7 is output (voltage 9) via the magnification switching circuit 8, and corrects the reference voltage 11 at the addition point 10. When the output current 4 fluctuates, the voltage 9 also fluctuates accordingly, and the reference voltage 11 is corrected at the addition point 10 accordingly. By inputting the corrected reference voltage 11 (voltage 3) to the current control circuit 2, the output current 4 is kept constant.

A block diagram of the constant current device 1 of FIG. 1 is realized.
FIG. 2 shows a constant current circuit 1 '. The reference voltage Vref is
Operational amplifier A₁Is input to the non-inverting input terminal. On the other hand,
Operational amplifier A₃, A₄, A₅, Wiring resistance R₃, R₄,
R₅, R₆Is the switch S₁, S ₂, S₃By choice
Operational amplifier A₃, A₄, A₅And wiring resistance R₃,
R₄, R ₅, R₆Are selected in combination. Selected
Operational amplifier A₃, A₄, A₅Output voltage increases
Width A₁Is input to the inverting input terminal. Operational amplifier A₁
Output voltage of FET ・ Q₁Input to the gate terminal of
Force current I₀Is adjusted and output. That is, the switch
S₁, S₂, S₃The output current can be selected by selecting
・ It is set.

The current detection resistor R₁Is calculated
Amplifier A₂Of the wiring resistance R₂of
The voltage drop is the operational amplifier A₂Input terminal of the
You. Operational amplifier A₂Output voltage of FET ・ Q₂Game
Input to the terminal. FET ・ Q₂Current I
₃Is the wiring resistance R in a stable state.₂Current I flowing through₂Same as
The same. On the other hand, the operational amplifier A₂And FET Q₂Work of
Thus, in a stable state, I ₁× R₁= I₂× R₂It is.
Therefore, in the stable state of this circuit, I₀= I₁= (R₂/ R₁) I₂= (R₂/ R₁) I₃  It is.

[0022] Here, when the output current _{I 0} varies, the current _{I 1} varies, the output voltage of the operational amplifier _{A 2} is varied.
Thereby also vary the output current _{I 3} of the FET · _{Q 2,} for example, when the switch _{S 1} is already on, the operational amplifier _{A 3}
Since the output voltage varies, thus also varies the output voltage of the operational amplifier A _1, I ₀ the FET · Q ₁ is varied suppressed.

As described above, in the constant current circuit 1 ', although the output current can be selected and set in a plurality of ranges, only _one high-precision and expensive current detection resistor (R ₁ ) is used. Further, the switches S ₁ , S ₂ , and S ₃ are not resistors for determining the magnification, but are operational amplifiers A ₃ , with the magnification set.
Since it is designed to switch between A ₄ and A ₅ , it is possible to eliminate an error factor due to on-resistance and leakage current without using expensive and high-precision switches. Therefore, the output current I ₀
Is controlled with high precision and constant. The operational amplifiers A3 to A3
5, the output current monitor signal 12 can be obtained.

FIG. 3 shows another embodiment of the constant current device of the present invention. The constant current device 50 is provided with a current control circuit 53 that controls the output current 52 to be able to output constantly based on the input voltage 51. The current detection circuit 54 converts the input current 55 into a voltage 56 and outputs it. The magnification switching circuit 57 is formed so that the current value of the output current 58 can be switched, and the output current 58 fluctuates according to the voltage 56.

Here, the current 55 input to the current detection circuit 54 is corrected by the current 58 output from the magnification switching circuit 57 at the combining point 60 by adding the output current 52 branched from the extraction point 59 of the output current 52. It is formed by this. Further, the voltage 51 input to the current control circuit 53 is formed by correcting the reference voltage 61 by the voltage 56 output from the current detection circuit 54. Therefore, even if the output current 52 fluctuates due to the influence of disturbance, it is output stably and constantly.

Further, the voltage 56 can be extracted from the extraction point 62 to monitor the output current 52 (output current monitor signal 63). Output current monitor signal 6
The full scale value of 3 is constant even if the range is changed by the magnification switching circuit 57. Therefore, for example, in a resistance measuring device, it can be input to an A / D conversion circuit (not shown) and used as a reference value for resistance measurement, thereby enabling highly accurate resistance measurement. In addition, the constant current device 50 has a shorter feedback loop than the constant current device 1 (FIG. 1), is statically more sensitive, has higher accuracy, and is stable against transient fluctuations. Circuit.

FIG. 4 shows a constant current circuit 50 'for realizing the constant current circuit 50 of FIG. Reference voltage Vref is connected to the non-inverting input terminal of the operational amplifier A _1. On the other hand, the selection of the switches S ₁ , S ₂ , S ₃ causes the operational amplifiers A ₃ , A ₃ ,
A ₄ and A ₅ are formed so that the wiring resistances R3, R4, R5 and R6 are selected in combination. The operational amplifier A ₃ ,
The inverting input terminals of A ₄ and A ₅ are connected to wiring resistances R ₃ and R _{4, respectively.}
The combination of the connection, the non-inverting input terminal of each is connected to the output of the operational amplifier A ₂ together with the inverting input terminal of the operational amplifier A _1. The outputs of the operational amplifiers A ₃ , A ₄ and A ₅ are connected to the gate terminal of the FET Q ₂ .

Furthermore, the output of the operational amplifier _{A 1} is FET ·
Is input to the gate terminal of Q _1, the drain terminal of the FET · Q ₁ is connected to the inverting input terminal of the operational amplifier A _2. Furthermore, the drain terminal of the FET · _{Q 2} of the FET · _{Q 1}
, A current detection resistor R ₁ and a wiring resistor R ₂
Is connected. Moreover the voltage drop across the wiring resistance R ₂ is connected to the non-inverting input terminal of the operational amplifier A _2, the output of the operational amplifier A ₂ is input to the inverting input terminal of the operational amplifier A _1. Here, the output current _{I 0} is outputted from the source terminal of the FET · Q1. In this circuit also, it is possible to take out the output current monitor signal from the output of the operational amplifier A _2.

Here, a specific example will be described below. Each wiring
The resistance is R₃= 9R₂/ 10, R₄= R₂/ 10, R₅= 9R₂
/ 10, R₆= R₂/ 10. Then switch S₁, S₂, S₃of
Wiring resistance R selected / set by selection₃, R₄,
R₅, R₆The magnification of S₁When selected ... R₂/ R₄= 10 S₂When selected ... R₂/ (R₃+ R₄) = 1 S₃When selecting ... [R₂/ (R₃+ R₄)] × [R₆/ (R
₅+ R₆)] = 0.1. Wiring resistance R₁= 10Ω, reference voltage Vref = 2
When the voltage is set to 00 mV, the switch S₁When you turn on
Operational amplifier A₁Reference voltage V applied to the non-inverting input terminal of
ref is the operational amplifier A₁Output in the + direction, F
ET / Q₁Increase the output current. This output current I₀Is
Current I₁Equal to the current I₁Is the current detection resistor R₁By
Voltage-converted, operational amplifier A₂Output voltage in the + direction
Add. Operational amplifier A₂Output voltage of the operational amplifier A₁of
The operational amplifier A ₁Output voltage
Then I₀Output current.

At the same time, the operational amplifier A₂Output voltage increases
Then, the operational amplifier A₃Output voltage increases,
Q₂Output current I₃Increase. Output current I₃increase of
And the wiring resistance R₄Of the operational amplifier A₃Anti
The voltage at the inverting input terminal becomes equal to the voltage at the non-inverting input terminal.
Where it equilibrates. At this time, the wiring resistance R₂FE
T ・ Q₂Current I through₃Current I equal to₂Was flowing
The wiring resistance R₂Has the wiring resistance R₄10 times the voltage drop
Is generated. Wiring resistance R₂Is the current I₁Raw
Current detection resistor R₁When the voltage drop is equal to
Amplifier A₂Output voltage is suppressed and stabilized. This time
Operational amplifier A₂Output voltage of the operational amplifier A ₁Entered in
Becomes equal to the reference voltage Vref.

At this time, the output current I ₀ is as follows: output current I ₀ = 200 mV / 10Ω × 10 = 200 mA.

Similarly, the switch S₂When you select
Operational amplifier A₄Operates and the wiring resistance R ₃+ R₄Voltage
Operational amplifier A₂With the output voltage of Therefore, R₂No electricity
The pressure drop is R₃+ R₄Becomes equal to Therefore, the output current I₀= 200 mV / 10Ω × 1 = 20 mA.

Furthermore, when selecting the switch _{S 3} is an operational amplifier _{A 5} is actuated, the first divided output voltage of the operational amplifier _{A 2} by R3 + R4 voltage wiring resistor R5 R6
/ 10. The voltage drop of the wiring resistance R2 is R3 + R
Equals 4. Therefore, the output current I ₀ = 200 mV / 10Ω × 0.1 = 2 mA

Here, the output current I₀Increase due to external factors
Then, the current I₁Also increases the operational amplifier A₂Output voltage increases
Add. Operational amplifier A₂The output voltage increase of the current I₁Suppress
Work in the direction of₀Is stable. Selected at this time
Operational amplifier A₃, A₄, A ₅Is the operational amplifier A₂Output
The voltage increase is transmitted to R2 via FET Q2, and the voltage of R2 is
The pressure acts to equal the voltage of R1. That is,
Operational amplifier A₂Output voltage is the output current I₀Follow the fluctuation of
Therefore, the output current I stably₀Can output
You.

Another constant current circuit for realizing the constant current device 50 of FIG. 3 is shown in FIGS. The operation and effect of these constant current circuits can be described in the same manner as the constant current circuit 50 'of FIG. FIGS. 8A and 8B show another embodiment of the magnification switching circuit 57 for switching the current of the output current.

[0036]

According to the first aspect of the present invention, it is only necessary to provide one expensive and highly accurate current detecting resistor despite the fact that the output current can be switched, thereby reducing the manufacturing cost. be able to. Further, an output current monitor signal can be extracted. According to the second aspect of the present invention, as in the first aspect, only one current detection resistor is required, and an output current monitor signal can be extracted.
Further, since the number of control elements in the feedback loop is reduced as compared with the first aspect, the output current can be controlled with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a constant current device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a constant current circuit according to FIG. 1;

FIG. 3 is a control block diagram of the constant current device according to the embodiment of the present invention.

FIG. 4 is a constant current circuit diagram according to FIG.

FIG. 5 is another constant current circuit diagram according to FIG. 3;

FIG. 6 is another constant current circuit diagram according to FIG. 3;

FIG. 7 is another constant current circuit diagram according to FIG. 3;

FIG. 8 is another constant current circuit diagram according to FIG. 3;

FIG. 9 is a control block diagram of a conventional constant current device.

10 is a conventional constant current circuit diagram according to FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 constant current device, 2 current control circuit, 3 voltage, 4 output current, 5 current detection circuit, 6 draw-out point, 7 voltage, 8 magnification switching circuit, 9 voltage, 10 addition Point, 11: Reference voltage, 12: Output current monitor signal, 50
... constant current device, 51 ... voltage, 52 ... output current, 53 ... current control circuit, 54 ... current detection circuit, 55 ... current, 56 ...
Voltage, 57: Magnification switching circuit, 58: Current, 59: Extraction point, 60: Addition point, 61: Reference voltage, 62: Extraction point, 63: Output current monitor signal, 64: Addition point, 100: Constant current Device, 101 ... output current, 102
... Lead-out point, 103… Addition point, 104… Reference voltage, 105… Voltage, 106… Current, 107… Voltage, 11
0: current control circuit, 111: operational amplifier, 112: FE
T, 120: Range changeover switch, 130: Current detection resistor

Claims (2)

[Claims] 1. A current control circuit formed so as to output a constant output current based on an input voltage, and a current detection circuit formed by converting the output current into a voltage and outputting the voltage. A circuit configured to switch the output voltage so that the output voltage is switchable, wherein the output voltage varies in accordance with the voltage output by the current detection circuit; The constant voltage device is characterized in that the voltage to be generated is formed by correcting the reference voltage by the voltage output from the magnification switching circuit. 2. A current control circuit formed to output a constant output current based on an input voltage, and a current formed to convert an input current to a voltage and output the voltage. A detection circuit, wherein the output current is formed to be switchable, and the output current is a magnification switching circuit that fluctuates in accordance with the voltage output by the current detection circuit;
The current input to the current detection circuit is formed by correcting the output current by the current output from the magnification switching circuit, and the voltage input to the current control circuit is the current detection circuit Wherein the voltage outputted by the constant current device is formed by correcting the reference voltage.