JPS58200609A - Insulation amplifier using differential transformer - Google Patents

Abstract

PURPOSE:To obtain a stable output with high accuracy, by providing a differential winding for an isolation transformer, forming the differential amplifier and applying negative feedback via the differential winding. CONSTITUTION:An input circuit of the primary winding N1 of the isolation transformer 1 is provided with a resistor R1 and a modulator 2 in series, and an output circuit of the secondary winding N2 is provided with a detector 3, and LPF4, and a high gain amplifier 5 in series. Further, the transformer 1 is provided with the differential winding N3 to induce a magnetic flux opposite to the magnetic flux induced in the primary winding N1 to form the differential transformer. Negative feedback is applied to the differential winding N3 by giving an output of the high gain amplifier 5 via a resistor R2 and a modulator 6. Through the forming of the circuit like this, an error component appearing at the output side is cancelled and the stable output with high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an isolation amplifier using a differential transformer, and aims to eliminate errors mixed into an output signal due to distortion in an insulation section and to improve stability.

Conventionally, in the field of industrial measurement, an isolation amplifier is known that amplifies an input signal to obtain an output signal while insulating input and output. There are various methods for this isolation amplifier, such as a photoelectric conversion method and a modulation method.

The isolation amplifier targeted by the present invention is one of the above-mentioned modulation type.

A modulation type isolation amplifier generally has a circuit configuration as shown in FIG. 37 in the figure is an isolation transformer, and the primary winding N/ of the isolation transformer 37 and three input terminals are connected through 33 modulators to form an input circuit, while the secondary winding N
The output side circuit configured on the A side is configured by connecting the detector 3da and the low frequency 6 wave generator 33'f1 to the secondary winding N, and the output of the low frequency 6 wave generator 3S is amplified by the amplifier 36. That's what I do.

In the above, the modulator 33 and the detector 3q are synchronously driven by the drive circuit 3, and the detector 3 is operated as a synchronous detector.

However, in the isolation amplifier using the modulation method described above, electrical distortion occurs due to nonlinearity in the insulation sections of the modulator 33, the detector J4', and the isolation transformer 3/, and changes in efficiency due to changes in the environmental temperature. Since the output appears without being reduced in any circuit, a large error is mixed into the output G4 and there is a problem of lack of stability.

However, in the above-mentioned isolation amplifier, the present invention configures a differential transformer by providing the isolation transformer with a differential winding for inducing a magnetic flux in the opposite direction to the magnetic flux produced by the primary winding. The input signal is By comparing the output signal with the output signal, the error introduced into the output signal due to the above-mentioned electrical distortion was canceled out, the stability of operation was improved, and the problems of the conventional method were solved.

The present invention will be explained below based on the embodiment shown in FIG. In the figure, l is an isolation transformer, and 1 of the isolation transformer l
A resistor R/(resistance value R/
) and the modulator-t@ column, and a detector, a low-frequency 6-wave amplifier, and a high-gain amplifier 5 are interposed in series in the output circuit on the secondary winding Na side. be. In addition, the above-mentioned isolation transformer l is provided with a differential winding N3 for inducing magnetic flux in the opposite direction to the magnetic flux induced in the primary winding N/, thereby forming a differential transformer. The output of the high gain amplifier S is applied to IJN3 via a resistor RJ (resistance value R, 2) and a modulator 6. In the above, the modulator 6 provided in the input side circuit, the detector 3 provided in the output side circuit, and the circuit connected to the differential winding, that is, the modulator 6 provided in the feedback circuit, are each synchronized by the drive circuit. As shown in Figure 2, ON, O1i'
This is an analog switch controlled by li'.

Now, in the isolated amplifier of the above embodiment, when a DC signal with a voltage E/ is applied between the input terminals 8, this DC signal is modulated into an AC signal by the modulator, and the primary winding ? tMN/ is il
An alternating current signal current flows. Ignoring the inductance of the primary winding IwNl, and considering the modulation by the modulator,
If the conduction ratio of the modulator is set to so%, the peak value I'm and the average value of the current i/ flowing through the input end circuit are 11 m, respectively. -E l /Rl ・ ・ ・
・ (C■, = El/CoR/ ...(C). Then, an alternating current magnetic field with a magnetic flux ψH/ is induced in the insulating transformer l by the primary winding mNl, and this causes the λ primary winding to An AC electromotive force called voltage ed is induced across N2. After this AC electromotive force is synchronously detected by the detector 3,
It is demodulated into a DC signal of voltage Ed by a low-frequency three-wave amplifier, and this DC signal is amplified by a high gain amplifier S. Output terminal as output of high gain amplifier S? The DC signal of the voltage E2 applied to the resistor Rxy is modulated into an AC signal by the modulator 6 again, and an AC signal current of 1-2 flows through the differential winding N3. The peak value I,m and the average value I, of the current i flowing through this differential winding N3 are I,m = E as in the input side circuit.
Ko/Rko...(3)1, =E,/2Rko・
...(da) becomes. A magnetic flux ψ11.2 in the opposite direction to the magnetic flux ψH/ is induced in the insulating transformer/. This magnetic flux ψH2 acts to cancel the magnetic flux ψH1y induced in the primary winding N/.

Therefore, the alternating current electromotive force c induced at both ends of the primary winding N
d is caused by the magnetic flux due to the difference between the absolute values of the magnetic flux ψII/ and ψ1■.If the high gain amplifier S is an ideal amplifier with infinite amplification, and the primary winding Kt and the differential Assuming that the number of turns of the winding N3 is equal and the resistance values of the resistors IR/RJ are equal, the following relationship holds between input and output. That is, if E co - ed - k · μ ... (!f) (k: conversion efficiency of demodulation system, μ: amplification degree of high gain amplifier) μ - ω, then cd = E co / k · μ → 0...(6) becomes. Therefore, 1ψH1l −lψH, zl=o ... (7) 1
1m = I, m + m
@ −(za)I, = I,
...(9), Hi = E
... ・(The relationship is /).

From the above, if we maintain symmetry between the circuit connected to the primary winding N/ and the circuit connected to the differential winding N3 and make the amplification ffY of the high-gain amplifier sufficiently large (for example, /θθ10,000 times ), the error component appearing in the output side circuit is canceled out, and the distortion generated in the demodulation system can also be reduced by the negative feedback effect. However, an output signal approximately equal to the DC signal applied to the input terminal can be stably obtained at the output terminal.

In the above, the resistance value of resistor R2 (including the resistance value of winding N/) and the resistance value of resistor It/(same (including the resistance value of winding N3)
By changing the ratio of (including the resistance value of), the ratio of human power to output can be changed in accordance with this change. Also, this change in the human output ratio can be achieved by changing the turns ratio between the primary winding N/ and the differential winding N3, but this can be done by changing the circuit resistance including the winding resistance, temperature characteristics, and aging. If the characteristics are not matched, sufficient differential operation will not be achieved, so it is necessary to maintain symmetry in the electrical characteristics between the circuits including both windings. ;.

As described above, according to the present invention, a differential winding that induces magnetic flux in the opposite direction to the magnetic flux produced by the primary winding is provided in the insulating transformer to constitute a differential transformer, and the electrical Since the characteristics are the same and negative feedback is applied through the differential winding,
This has the effect of providing highly accurate and stable output.

[Brief explanation of the drawing]

Fig. 7 is a block circuit diagram of an embodiment of the present invention, Fig. 2 is the same (operational diagram of the modulator and detector in the embodiment), and Fig. 3 is a block circuit diagram of a conventional isolation amplifier. Isolation transformer 6...Modulator 3...Detector DA...Low frequency waveform generator 5...High gain amplifier 7
・・Drive circuit・・Input terminal 9・・Output terminal Patent applicant Takashi Yamashita Agent □ Tadashi Suzuki 7

Claims (1)

[Claims] l An input side circuit is connected to the primary winding of an isolation transformer, and λ
In an isolation amplifier comprising an output circuit connected to a secondary winding, the isolation transformer is provided with a differential winding for inducing a magnetic flux in the opposite direction to the magnetic flux caused by the primary winding. An isolated amplifier using a differential transformer, characterized in that the differential winding and the output side circuit are connected via an amplifier to provide negative feedback. is an isolation amplifier using a differential transformer according to claim 1, which maintains symmetry in electrical characteristics.