JPH011014A - Voltage-current conversion circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage-current conversion circuit, and particularly to a circuit technique that is effective when applied to a motor drive circuit.

[Conventional technology]

"Practical Design of Analog Circuits" (first edition published March 30, 1980, published by CQ Publishing, p. 56) K describes an example of a voltage-current conversion circuit using an operational amplifier.

Its outline includes a first operational amplifier that obtains an output current corresponding to an input voltage, a current detection resistor that supplies the output current to a load and detects a change in the output current, and a first operational amplifier that detects a change in the output current. and a second operational amplifier that feeds back to the operational amplifier, and drives the load circuit with a constant current.

However, in the above circuit configuration, since the output current is unipolar, it is not possible to control, for example, a motor or the like to rotate in forward and reverse directions.

Therefore, the present inventor developed a voltage-current conversion circuit ttBTL (
Balanced Transformer Less)
In addition to switching the polarity of the output current, we also considered simplifying the circuit configuration.

Although the following is not a publicly known technique, it is a technique studied by the present inventor, and its outline is as follows.

That is, an input voltage is commonly supplied to each inverting input terminal of the two operational amplifiers, and each non-inverting input terminal is set to a reference voltage, thereby configuring the first and second inverting amplifiers. Further, a load circuit is connected between the output terminals of the first and second inverting amplifiers via a d photodetection resistor. The current flowing through the load circuit, in other words the amount of output current, is detected by a current detection resistor and fed back to the inverting input terminal of the second inverting amplifier.

According to the above circuit configuration, the polarity of the output 'Ilt current corresponds to a change in the polarity of the input voltage, so that the load circuit can be driven bidirectionally. Furthermore, since constant current control cannot be performed by the current detection resistor and feedback circuit, the load can be driven at a constant current, and the circuit configuration is simplified because no operational amplifier is used for output current detection and feedback. There is.

However, according to the studies conducted by the present inventors, it has been found that there is still room for improvement as described below.

[Problem that the invention seeks to solve]

In other words, for the impedance of the load circuit, the first
And if the gain of the second inverting amplifier is not optimally designed,
A phenomenon called so-called one-sided clipping occurs. To prevent this phenomenon from occurring, it is necessary to set the reference voltage supplied to each non-inverting input signal to 70-degrees.

Therefore, the inventor of the present invention thought that the above problem could be solved by devising the feedback circuits of the first and second inverting amplifiers, and came to propose the present invention.

An object of the present invention is to provide a voltage-to-current conversion circuit with a simple circuit configuration that is BTL-connected.

Another object of the present invention is to provide a voltage-current conversion circuit suitable for constant current driving of a motor.

The above and other objects and novel features of the present invention will become apparent from the present specification and the accompanying drawings.

[Failure to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a control voltage is supplied to the first inverting amplifier (1), and its phase-inverted output voltage is supplied to the second inverting amplifier (2).
). Furthermore, the first and second inverting amplifiers (
A load circuit is connected between each output terminal of 11(2) via a current detection resistor (Rs). The change in the output current obtained by the current detection resistor is fed back so as to be superimposed on the reference voltage of the first inverting amplifier (1).

[Effect]

According to the above-mentioned means, the output voltage of the first inverting amplifier (1) has an opposite phase with respect to the phase change of the control voltage, and the output voltage of the second inverting amplifier (2) has the same phase. ,
It should be possible to switch the direction of the output current in response to changes in the phase of the control voltage, and drive the load circuit bidirectionally. Furthermore, the gain of the first inverting amplifier (1) is controlled by the amount of change in the output current, and the output voltage is supplied to the second inverting amplifier (2). (There is no inconvenience such as the occurrence of one-sided clipping due to the gain difference of 21, and the constant current drive of the load circuit becomes 0T performance.

In addition, since the feedback circuit can be configured with a resistor, the circuit configuration can be simplified, making it easier to implement a semiconductor integrated circuit (hereinafter referred to as an IC), and further reducing the chip area and improving the degree of integration. Can be done.

〔Example〕

Hereinafter, one embodiment of a voltage-current conversion circuit to which the present invention is applied will be described with reference to FIG. Note that the drawing is a circuit diagram showing an example of application to a motor drive circuit, and although not particularly shown, it is assumed that the circuit is implemented as an IC.

The first inverting amplifier 10 has an input resistor R3 at the inverting input terminal.
■ Control voltage through. tl is supplied, and the non-inverting input terminal is set to the reference voltage Vref via a resistor R8. Note that the resistor Rt is a feedback resistor, and the inverting amplifier 1
The gain AV is Av=-R.

/R+ (Vctl-Vref), but in this embodiment, for convenience of explanation, it is assumed that the gain is set to 1. Output voltage of inverting amplifier 1■. 1 is Vctl
>Vref, it becomes low level, and Vctl<Vre
It becomes high level when f.

The above output voltage V. I is supplied to the second inverting amplifier 2 via a resistor R8. Note that R6 is a feedback resistor, and the gain AV of the second inverting amplifier 2 is Av=-Rs/Ra(
In this embodiment, it is assumed that the gain is set to 1 as described above.

Output voltage v0. of inverting amplifier 2. is the above output voltage V,
The phase of the control voltage V is reversed with respect to the control voltage V. tl
The level changes with the same phase.

Therefore, the control voltage V. ti and the reference voltage Vref are V
When ctl > Vref, the output voltage V01 is low level, and the output voltage is ■. , reaches a high level. The motor coil R1 (corresponding to the load circuit) and the current detection resistor R8K output 'DC I' in the direction shown. In other words, driving direct current flows.

On the other hand, if Vctl < Vref, the output voltage V
. l is high level, output voltage V. , changes to low level, and the polarity of the output current I0 changes to the opposite polarity.

The output current Io flows through the current detection resistor R, and the resistor R
, I at both ends. A voltage drop Vs determined by -Rs occurs and is transmitted to the non-inverting input terminal of the inverting amplifier 1 at l- via the feedback resistor R4. And the reference voltage of the inverting amplifier 1 is V
The partial pressure v1 is determined by rcf+Vs, and the above-mentioned one-sided clip is eliminated, but this will be proven using a mathematical formula.

First, regarding the inverting amplifier 1, the voltage level of the inverting input terminal also approaches the voltage V, so when the current I0 flows in the direction of the arrow, the voltage v8 becomes vs '' V ol + I.・R8・・・・・・・・
・・・・・・・・・・・・・・・ (2) Also, regarding the non-inverting input terminal of the inverting amplifier 1, from the above formula (2H3), on the other hand, regarding the inverting input terminal of the inverting amplifier 20, here Rs ” Ra ・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(6) and D1, output voltage V. , is Vow = 2 Vref Vo+...
・・・・・・・・・・・・・・・・・・・・・ (7) Furthermore, output current engineering. When calculating, from the above equations (7) and (8), the above (11 (4) (in equation 91, R, = R1...
・・・・・・・・・・・・・・・・・・ 0IR,=R4
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・ If aυ, then the output voltage ■ from the above (1)'(4)'(9)'. ,
seek.

Furthermore, from the above formula (7)03, the output voltage v0. , the output voltage V0.
, V. , but by comparing both equations, it can be seen that the voltage level is determined by the same elements.

Therefore, the output voltage V. l + vo, will be clipped simultaneously.

The voltage-current conversion circuit shown in the above embodiment has the following effects.

(1) a first inverting amplifier to which a control voltage is supplied;
a second inverting amplifier to which the output voltage of the first inverting amplifier is supplied; and a load circuit connected to each output terminal of the first and second inverting amplifiers; By providing a current detection resistor and a feedback circuit to control the gain of the operational amplifier, and controlling the output voltages of the first and second operational amplifiers under the same conditions, it is possible to reduce one-sided clipping of the output voltage. can get.

(2) The above (1) provides the effect that stable constant current driving can be performed even if the impedance of the load circuit varies.

(3) According to (1) above, the phase of the output current changes in response to the change in the phase of the control voltage, so it is possible to drive the load circuit bidirectionally.

(4) Since the feedback circuit that feeds back the change in the output current to the first inverting amplifier is constituted by a negative resistor, the effect of simplifying the circuit configuration can be obtained.

(5) According to (3) above, the voltage-current conversion circuit can be easily integrated into an IC.

(6) According to (3) and (4) above, the chip area can be reduced when integrated into an IC, and the degree of integration can be improved.

Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above examples, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say.

For example, the gains of the first and second operational amplifiers are not limited to 1, and may be set arbitrarily. Also, resistor R1 can be deleted. Furthermore, the current detection resistor may be formed inside the IC, but if the output current is a large current, it may be provided outside the IC.

In the above explanation, the invention made by the present inventor is applied to a motor drive circuit, which is the field of application that formed the background of the invention, but the invention is not limited to this, and It can be used to drive the optical system focus adjustment coil. Furthermore, when used as a motor drive, it can be used in a two-phase brushless motor drive circuit or a vCM (voice coil motor) drive circuit.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, a load circuit and this load are connected between the output terminal of the ml inverting amplifier to which the limiting voltage is supplied and the output terminal of the second inverting amplifier to which the output voltage of the first inverting amplifier is supplied. A current detection resistor is provided to detect a change in the current flowing through the circuit, and the current change is fed back to the first inverting amplifier for gain control, so that it can be adapted to the impedance of the load circuit. The load circuit can be driven with a constant current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a pressure-current conversion circuit to which the present invention is applied. 1.2...Inverting amplifier, R1-R7...Resistor, R8
...Current detection resistor, R1...Load circuit, Vref.
...Reference voltage, engineering. ...output current (drive current),
Vctl...control voltage, ■. l*Vat...Output voltage. Agent: Patent Attorney Katsuo Ogawa )−ノ′

Claims (1)

[Claims] 1. A first inverting amplifier that obtains a first output voltage whose level changes and whose phase is inverted in accordance with the control voltage; and a second inverting amplifier which obtains a second output voltage whose phase is inverted from the first output voltage. an inverting amplifier, a current detection resistor that detects the amount of output current flowing between each output terminal of the first and second inverting amplifiers, and a current change amount obtained by the current detection resistor is transferred to the first inverting amplifier. and a feedback circuit that performs gain control by feeding back to the voltage-current conversion circuit.