JPH0724003B2 - Constant current drive - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a constant current drive device for supplying a constant current to a load.

[Technical background of the invention and its problems]

Conventionally, as a constant current driving device for a load whose inductance or impedance changes, such as a coil or a linear motor, or an unknown load, there is a device shown in FIGS. 3 and 4.

The circuit shown in FIG. 3 applies an input voltage V _O between a non-inverting input terminal (+) of an operational amplifier (hereinafter referred to as an operational amplifier) OP and a ground line (ground line), and connects it in series with a load Z _L. The voltage generated in the connected sensing resistor R _SC is negatively fed back to the inverting input terminal (−) of the operational amplifier OP, and the load current I _L is supplied from the output terminal of the operational amplifier OP to the load Z _L. is there. + V _CC and −V _CC are the positive and negative sides of the power supply voltage, respectively.

In the circuit shown in FIG. 4, the input voltage V _O is applied to the inverting input terminal of the operational amplifier OP via the resistor R ₁ , and the negative feedback resistance R ₂ is applied between the inverting input terminal and the output terminal of the operational amplifier OP. Connect
The voltage generated across the load Z _L is divided by the voltage dividing resistors R ₃ and R ₄ and applied to the non-inverting input terminal of the operational amplifier OP.

However, in the circuit configurations shown in FIGS. 3 and 4, the range of constant current operation is limited by the relationship of I _L <(V _CC / Z _L ), so for a large impedance load exceeding this range. Constant current operation is not possible. For example
When V _CC is ± 15V, in order to supply a constant current of 1A to the load Z _L , the impedance of the load R _L must be 15Ω or less.If the load R _L changes to 15Ω or more, the circuit Cannot perform constant current drive operation.

To solve this, it is sufficient to increase the value of the power supply voltage V _CC , but it may be difficult to increase the value of V _CC due to the rating of the operational amplifier used, restrictions on the design of the driving power supply, etc. Many, or even if this is ignored, the reliability of the constant current drive device is low.

[Object of the Invention]

The present invention has been made based on the above circumstances, and an object of the present invention is to expand a maximum amplitude of a load applied voltage without increasing a power supply voltage, and thus, even for a load whose impedance largely changes. An object of the present invention is to provide a constant current drive device that operates stably and has high reliability.

[Outline of Invention]

The present invention relates to a constant current drive device for supplying a constant current according to an input voltage to a load, and a first operational amplifier and the first operational amplifier.
First resistor R5 connected to the non-inverting input of the operational amplifier of
A second resistor Rsc connected to the output terminal of the first operational amplifier, and a second resistor Rsc connected between the other end of the second resistor Rsc and the non-inverting input terminal of the first operational amplifier. Third resistor R6
And a fourth resistor R7 connected between the inverting input terminal and the output terminal of the first operational amplifier, wherein the input voltage is supplied to the first operational amplifier via the first resistor R5. The output voltage of the first operational amplifier, which is applied to the non-inverting input terminal of the amplifier, is applied to one end of the load through the second resistor Rsc, and the constant current control of the current of the load is performed. And a second operational amplifier having a non-inverting input terminal grounded and an output terminal connected to one end of the load, and an inverting input terminal of the second operational amplifier and the first operational circuit. Fifth resistor R8 connected between the inverting input of the operational amplifier
And a sixth resistor R9 connected between the inverting input terminal and the output terminal of the second operational amplifier to generate a voltage having a phase opposite to that of the output voltage of the first amplifier circuit. A second amplifier circuit for applying a voltage to the other end of the load, R5
= R7 = R8 = (1/2) R9 = R6 + Rsc
By widening the maximum amplitude of the load applied voltage without increasing the power supply voltage, stable operation is achieved even with a load whose impedance changes significantly.

Example of Invention

 Hereinafter, the present invention will be specifically described with reference to examples.

FIG. 1 is a circuit diagram of a constant current drive device as an embodiment of the present invention. This device basically comprises a first amplifier circuit 10 and a second amplifier circuit 11.

The first amplifier circuit 10, which performs constant current control of the load current by the positive feedback of the change in the load current is applied with the output voltage to one end of the load Z _L, an operational amplifier (op amp) OP ₁ , a resistor R ₅ connected to the non-inverting input terminal of the operational amplifier OP _1, a Senjingu resistance R _SC connected to the output terminal of the operational amplifier OP _1, the non-inverting input of the other end and the operational amplifier OP ₁ of Senjingu resistor R _SC Resistance R connected between the ends
₆ and a resistor R ₇ connected between the inverting input terminal and the output terminal of the operational amplifier OP ₁ . The input voltage V _O is applied to the non-inverting input terminal of the operational amplifier OP ₁ via the resistor R ₅ , and
The output voltage of the operational amplifier OP ₁ is applied to one end of the load Z _L via the sensing resistor R _SC .

Then, the second amplifier circuit 11 is the first amplifier circuit.
A voltage having a phase opposite to that of the output voltage of 10 is generated, and this voltage is applied to the other end of the load Z _L.
2 , a resistor R ₈ connected between the inverting input terminal of the operational amplifier OP _{2 and} the inverting input terminal of the operational amplifier OP ₁ in the first amplifier circuit 10, the inverting input terminal and the output terminal of the operational amplifier OP ₂ , And a resistor R ₉ connected between. The non-inverting input terminal of the operational amplifier OP ₂ is grounded, and the output terminal thereof is connected to the other end of the load Z _L. Each resistor R ₅
Between R ₉ and R _SC , their values are determined so that the following relationship holds.

R ₅ = R ₇ = R ₈ = (1/2) R ₉ = R ₆ + R _SC (1) Next, the operation of the embodiment apparatus configured as described above will be described.

When the input voltage V _O is applied to the non-inverting input terminal of the operational amplifier OP ₁ via the resistor R ₅ , an output voltage corresponding to the value of the input voltage V _O is output from the operational amplifier OP ₁ and the sensing resistor R _SC
Is applied to the load Z _L via. On the other hand, since the operational amplifier OP ₂ acts as an inverting amplifier, a voltage having a phase opposite to the output voltage of the operational amplifier OP ₁ appears at the output terminal of the operational amplifier OP ₂ , and this voltage is applied to the other end of the load Z _L. When the load current changes due to the change in the impedance of the load Z _L , the current change is detected by the sensing resistor R _SC , and the detection result is fed back via the resistor R ₇ , so that the load current can be made constant. .

Here, the voltage and current of the main part in this embodiment are as follows.

_{I 0 = (V 0 -V 1} ) / R 5 ... (2) V 2 = V 1 -I 0 R 6 = (R 5 + R 6) / R 5 · V 1 -R 6 / R 5 · V 0 ... _{(3) I 1 = V 1} / R 8 ... (4) V 3 = V 1 + I 1 · R 7 = 2V 1 ... (5) I 2 = (V 3 -V 2) / R SC ... (6) = [2V ₁ -{(R ₅ + R ₆ ) / R ₅・ V ₁ −R ₆ / R ₅・ V ₀ }] / R _SC = V ₁ / R ₅ −V ₀ / R ₅ + V ₀ / R _SC (∵ from _{R 6 = R 5 -R SC)} ... (7) I 1 = I 0 + I 2 = V 0 / R SC (∵R 5 = R 8) ... (8) V 4 = -V 3 ... (9) or , the load Z current flowing in _L I _L can be determined constant by the load Z input voltage V _O regardless of the size of the _L and the sensing resistance R _SC. At this time, across the load Z _L , if V ₂ is positive, V ₄ becomes negative, and conversely, if V ₂ is negative, V ₄ becomes negative.
Is positive, the potential difference is close to 2 V _CC maximum.

Therefore, despite using the same power source as before,
The impedance range of the load capable of constant current operation is doubled as compared with the conventional one (Figs. 3 and 4). For example, V _CC
Is ± 15 V, constant current operation can be performed on a load whose impedance changes up to 30 Ω.

Next, another embodiment of the present invention will be described with reference to FIG. The constant current drive device shown in FIG. 2 is also configured to have a first amplifier circuit 20 and a second amplifier circuit 21 as in the case of the device shown in FIG. 1, but they are different in the following points. That is, the other end of the resistor R ₁₂ connected to the inverting input end of the operational amplifier OP ₁ is connected to the ground line, and the resistor R ₁₁ is connected between the output end of the operational amplifier OP ₁ and the inverting input end of the operational amplifier OP _2. Has been done.

Even with this configuration, a maximum potential difference of approximately 2 V _CC can be generated between both ends of the load Z _L , so that the same effect as that of the above embodiment can be obtained.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the above embodiments and various modifications can be made.

For example, in FIGS. 1 and 2, ± V _CC is the power supply voltage with reference to the ground potential, but −V _CC is the ground level,
The ground level in Fig. 1 and Fig. 2 is 1/2 V _CC or the potential level around it (hereinafter referred to as common level V _COM ).
_Is the potential difference between the input voltage V _O and the common level V _COM.
V _O ′ allows a current I _L = V _O ′ / R _SC to flow through the load. This load current I _L flows between + V _CC and the ground line and is independent of the common level V _COM . Therefore,
The V _COM source does not need to be low impedance, + V
_Since it can be easily generated from _CC , such a circuit configuration is suitable as a circuit used with only one power supply (for example, + V _CC = 30V).

In the above embodiment, the load current I _{L is set} to the operational amplifiers OP ₁ and OP.
_Although it is supplied from the output terminal of ₂ , it may be preferable to provide a current buffer or the like in the final stage in consideration of the ratings of the operational amplifiers OP ₁ and OP ₂ .

Although the use of the operational amplifiers OP ₁ and OP ₂ is extremely advantageous in terms of circuit configuration, it goes without saying that they can also be configured using transistors or the like.

〔The invention's effect〕

As described above in detail, according to the present invention, since the maximum amplitude of the load applied voltage can be widened without increasing the power supply voltage, stable operation is achieved even with a load whose impedance changes significantly, and the reliability is high. A constant current drive device can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a constant current driving device as one embodiment of the present invention, FIG. 2 is a circuit diagram of another embodiment device of the present invention, and FIGS. 3 and 4 are conventional constant current driving devices. It is a circuit diagram. 10,20 …… First amplifier circuit, 11,21 …… Second amplifier circuit, V _O …… Input voltage, Z _L …… Load, OP ₁ , OP ₂ …… Operational amplifier.

Claims (2)

[Claims] 1. A constant current drive device for supplying a constant current according to an input voltage to a load, and a first operational amplifier and a first resistor connected to a non-inverting input terminal of the first operational amplifier.
R5 and a second output connected to the output of the first operational amplifier
Resistor Rsc and a third resistor connected between the other end of the second resistor Rsc and the non-inverting input end of the first operational amplifier.
R6 and a fourth resistor R7 connected between the inverting input terminal and the output terminal of the first operational amplifier, wherein the input voltage is the first resistor R5 and the first resistor R5. The output voltage of the first operational amplifier, which is applied to the non-inverting input terminal of the operational amplifier, is applied to one end of the load via the second resistor Rsc, and is a constant current of the current of the load. A first amplifier circuit for controlling, a second operational amplifier whose non-inverting input terminal is grounded, and whose output terminal is connected to one end of the load, and an inverting input terminal of the second operational amplifier and the first operational amplifier. Fifth resistor R8 connected between the inverting input of the operational amplifier
And a sixth resistor R9 connected between the inverting input terminal and the output terminal of the second operational amplifier to generate a voltage having a phase opposite to that of the output voltage of the first amplifier circuit. A second amplifier circuit for applying a voltage to the other end of the load, R5
= R7 = R8 = (1/2) R9 = R6 + Rsc The constant current drive device characterized by satisfying the conditions. 2. A constant current drive device for supplying a constant current according to an input voltage to a load, comprising: a first operational amplifier; and a first resistor connected to a non-inverting input terminal of the first operational amplifier. , A second resistor connected to the output of the first operational amplifier, and a third resistor connected between the other end of the second resistor and the non-inverting input of the first operational amplifier. A resistor, a fourth resistor connected between the inverting input terminal and the output terminal of the first operational amplifier, and a fifth resistor connected to the inverting input terminal of the first operational amplifier and the other end of which is grounded. A resistor, the input voltage is applied to the non-inverting input terminal of the first operational amplifier via the first resistor, and the output voltage of the first operational amplifier is the second resistor. Is applied to one end of the load through the first increase control for constant current control of the current of the load. A circuit, a second operational amplifier having a non-inverting input terminal grounded and an output terminal connected to one end of the load, an inverting input terminal of the second operational amplifier and an inverting input terminal of the first operational amplifier. A sixth resistor connected between the second operational amplifier, the seventh resistor connected between the inverting input terminal and the output terminal of the second operational amplifier, the output terminal of the first operational amplifier and the second resistor. And an eighth resistor connected between the non-inverting input terminal of the operational amplifier and the non-inverting input terminal of the operational amplifier, and a voltage having a phase opposite to that of the output voltage of the first amplifier circuit is generated. A constant current drive device comprising: a second amplifier circuit for applying a voltage.