JPH04138383A - Dc-ac conversion circuit - Google Patents

Abstract

PURPOSE:To execute a highly precise control of a current including a current of high frequency without using any specific component, by holding the intermediate potential of two AC output terminals at 1/2 of a DC power source and by dividing a load into two parts having an equal impedance. CONSTITUTION:A DC-AC circuit 2 is connected to a DC power source 1, while a load 10 and a current detecting circuit 4 are connected onto the single-phase AC output side of the circuit 2, and a feedback control is executed by a detected load current of the circuit 4. On the occasion, potentials Vo 1 and Vo 2 of two output terminals on the AC output side are inputted to an output potential control circuit 11 and thereby the intermediate potential thereof is always controlled to be 1/2 of an input voltage Vs. The load 10 is divided into two parts having an equal impedance and the circuit 4 is connected to the middle thereof. Thus, the potential of the circuit 4 is always held at 1/2 of the voltage Vs. By adding one variable resistor as a trimmer and by executing CMRR regulation, the CMRR regulation can be mede zero without dependence on the frequency of a reference signal 5. Accordingly, a highly precise feedback control can be executed.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention is utilized in the field of DC-AC conversion.

The present invention relates to a DC-AC conversion circuit, and more particularly to a DC-AC conversion circuit that performs feedback control of a load current on an AC output side, and particularly relates to improvement of load current detection error.

(b) Conventional technology A conventional example is illustrated in FIG.

A DC power supply 1 is input to a DC-AC conversion circuit 2, and an AC output is applied to a load 3. Such a DC-AC conversion circuit 2 generally uses a transistor, a thyristor, or the like.

The resulting current is detected by a current detection circuit 4, this detection signal is compared with a reference signal 5 by an adder 6, and its error signal is amplified by an amplifier 9 and input to a drive circuit 7.

The drive circuit 7 drives internal switching elements (not shown) of the DC-AC conversion circuit 2.

This ensures that the error signal is zero, i.e.
The load current is controlled to be equal to the reference signal.

Note that 8 is a detection resistor.

(c) Problems to be Solved by the Invention Although a differential amplifier type is often used for the current detection circuit 4, the potential of the point where its input terminal is connected to GND fluctuates depending on the reference signal. Therefore, the common mode rejection ratio CMRR (Common Mode
There is a detection error due to insufficient RejectionRatio). It is known that the larger the CMRR value, the more accurately the differential signal buried in the common mode signal can be amplified.

In recent years, there has been a demand for increased output voltage and response up to high frequencies, and errors due to CMRR have become significant, affecting accuracy.

FIG. 4 illustrates the characteristics of CMRR versus frequency, and the higher the frequency, the smaller the CMRR value.

Therefore, in order to guarantee sufficient CMRR at high frequencies,
It is also necessary to select components such as resistors that have excellent high-frequency characteristics, but due to power consumption limitations due to the increase in output voltage, it is necessary to use high-resistance components that do not have good high-frequency characteristics. As a result, a problem arises in that it is difficult to improve CMRR.

Furthermore, when an impedance is connected to the load, the higher the frequency, the greater the ratio of voltage and current (voltage/current), so the influence of errors due to CMRR becomes more significant.

Here, we took a differential amplifier type as an example for the current detection circuit 4, but
A similar problem exists in isolation amplifiers.

An object of the present invention is to provide a DC-AC conversion circuit that is capable of precise current control up to high frequencies without using special components with excellent high frequency characteristics.

(d) Means for solving the problem The above object consists of a DC-AC converter circuit connected to a DC power supply, and a load and a current detection circuit are inserted on the single-phase AC output side, and the detection load A DC-AC conversion circuit of the type that performs feedbank control of the current is equipped with a circuit that maintains the intermediate potential of the two AC output terminals in the DC power supply 172, and divides the load into two parts with equal impedance.
This is achieved by arranging a current detection circuit having an internal resistance for the trimmer between them.

(e) The potential of the load current detection circuit on the AC output side becomes the intermediate potential between the two output terminals and is constant with respect to GND, so
Errors caused by CMRR can be minimized.

(f) Example A preferred embodiment of the invention will be explained based on the drawings.

FIG. 1 is a circuit diagram showing one embodiment thereof.

The outline is the same as the conventional example shown in FIG. 3 described above.

According to the present invention, the potentials Vol and Vo2 of the two output terminals on the AC output side are input to the output potential control circuit 11, and as shown in FIG. 2, the intermediate potential is always 1/2 of the input voltage Vs. controlled so that

Further, the load 10 is divided into two parts having equal impedance, and the current detection circuit 4 is connected between the two parts.

As a result, the potential of the current detection circuit 4 is always set to the input voltage V
Since it is held at 1/2 of s, the CMRR error can be minimized by considering only the DC value from the characteristic diagram of FIG.

That is, by adding one variable resistor as a trimmer to the current detection circuit 4 and performing CMRRII adjustment, the CMRR error can be made zero regardless of the frequency of the reference human power 5. This enables highly accurate feedback control up to high frequencies.

(g) Effects According to the present invention, accurate current control up to high frequencies can be realized during feedback without using special components with excellent high frequency characteristics.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is a diagram illustrating control of two output potentials according to the present invention, Fig. 3 is a circuit diagram of a conventional example, and Fig. 4 is an example of frequency versus CMRR characteristics. It is a diagram. 1 is a DC power supply, 2 is a DC-AC conversion circuit, 3 and 10 are loads, 4 is a current detection circuit, 5 is a reference signal, 7 is a drive circuit, and 11 is an output potential control circuit. Utility model registration applicant Shimadzu Corporation

Claims (1)

[Claims] 1. In a type of DC-AC conversion circuit that consists of a DC-AC conversion circuit connected to a DC power source, a load and a current detection circuit are inserted on the single-phase AC output side, and the detected load current is feedback-controlled. , is equipped with a circuit that maintains the intermediate potential of the two AC output terminals at 1/2 of the DC power supply, divides the load into two parts with equal impedance, and a current detection circuit having an internal resistance for the trimmer is placed between them. A DC-AC conversion circuit characterized by: