SU1075176A2 - Linear converter of ac voltage effective value - Google Patents

Abstract

LINEAR VARIABLE VOLTAGE TRANSMITTER by autol. 741167, which is characterized by the fact that, in order to increase the conversion accuracy, an adder is inserted into the circuit between the output terminal of the low-pass filter and the drain of the first field-effect transistor and an adder is connected to the circuit of the output low-pass filter terminal and the drain of the first field-effect transistor. transistor. {% (L cd

Description

The invention relates to electrical measuring equipment and is intended for use in the construction of analog and digital AC voltmeters.

According to the main auth. No. 741167 is known for a linear variable voltage transducer with two field-effect transistors, the gates of which are connected to each other, an imbalance amplifier connected between the source yi gate of the first field-effect transistor, a low-pass filter, the output terminal of which is connected to the output terminal of the device and the drain of the first field-effect transistor, the first inverting amplifier and the first resistor, connected in series between the output terminal of the low-pass filter and the source of the first field tract ican, second inverting amplifier and a second resistor connected in parallel between the source of the second FET and an input terminal of the low pass filter, a third resistor between the source exception in the first field effect transistor and vhodnoy.klemmoy device

connected to the drain of the second field-effect transistor l.

A disadvantage of the known device is associated with a low conversion accuracy due to the presence of an error due to temperature and time drift of the bias voltage bias voltage. The indicated raid causes a change in the constant potential of the source of the first field-effect transistor, i.e. change of constant voltage source - drain

1. A field-effect transistor, so that to compensate for the alternating current flowing through the third resistor, the amplitude of conduction oscillations of the first field-dependent transistor is required.

The aim of the invention is to increase the accuracy of the conversion provided by such a device. The goal is to achieve that in the linear transducer of the effective value of the alternating voltage, containing two field-effect transistors, the gates of which are connected to each other, an unbalance amplifier connected between the source and gate of the first field-effect transistor, low-pass filter, the output terminal of which is connected to the output terminal devices and with the drain of the first transistor, the first inverting amplifier and the first resistor connected in series between the output terminal of the low-pass filter and the source ohm of the first field-effect transistor, the second inverting amplifier and the second resistor connected in parallel between the source of the second field-effect transistor and the input terminal of the low-pass filter, the third resistor connected between the source of the first field-effect transistor and the input terminal of the device connected to the drain of the second field-effect transistor in the circuit between the output terminal of the frequency filter and the drain of the first field-effect transistor, a sum torus is inserted, the other input terminal of which is connected to the source of the first field-effect transistor.

The drawing shows a functional diagram of the proposed linear transducer of the effective value of the alternating voltage.

The device contains the first 1 and second 2 field-effect transistors, the gates of which are connected to each other, the unbalance amplifier 3 connected between the source and the gate of the field-effect transistor 1, a low-pass filter 4, the output terminal of which is connected to the output terminal of the device and through an adder (non-inverting) 5 another input connected to the source of the field-effect transistor 1, - with the drain of the latter, the first inverting amplifier. 6 and the first resistor 7 connected in series between the output terminal of the low-pass filter 4 and the source of the field-effect transistor 1, the second inverting amplifier 8 and the second resistor 9 connected in parallel between the source of the field-effect transistor 2 and the input terminal of the low-pass filter 4, the third resistor 10 connected between the source of the field-effect transistor 1 and the input terminal of the device connected to the drain of the field-effect transistor 2.

The device works as follows.

The input of the unbalance amplifier 3 is supplied by alternating current through resistor 10, proportional to the ionic voltage measured by I) e (i), and through inverting amplifier 6 and resistor 7 to direct current proportional to the voltage of low frequencies 4 and 4 devices in general. To the same input of the unbalance amplifier 3, through the adder 5, designed to sum the DC voltages, and the field-effect transistor 1 is supplied with a current proportional to the sum of the DC voltage if the bias of the unbalance amplifier 3 and DC, voltage is Ch d, | | . The unbalance amplifier 3 is covered by parametric negative feedback through the field-effect transistor 1, therefore, when the input voltage U is applied to t), the output voltage unbalance causes a change (modulation of the conduction of the channel of the field-effect transistor 1 and simultaneously changes the conductivity of the channel of the field-effect transistor 2, Module dependence Conduction Ci of the field-effect transistor 1 from the input voltage and eh U) t of the bias voltage and see the unbalance amplifier 3 and the output voltage of the converter can be determined from the condition It is assumed that the sum of the currents to the input of the unbalance amplifier 3 is zero,) 7 CM l Bbix-cw O, where (-jH G jo conductivity resistors ° 7 and 10. It follows from equation (1) that UcM g. VxM (2) C, -C,; j4 (C, 4C ,, o Bbiic you Since the input of an inverting amplifier 8 through a drop of a field-effect transistor 2 with conductivity C, receives a current equal to C in (t) d I then the output This amplifier has the voltage (3) where Qg is the conductivity of the resistor 9. The conductivities of the channels of field-effect transistors placed in the same crystal are the same, TeQ-Q, therefore, substitute the value Q from equation (2) into the equation e (.3), we obtain G,. , , o) G.o Vj, h i -lAU -l / W. H) Qq UBX Ivyx (1) The voltage Ug is averaged by a low-pass filter 4. As a result, the average value of the output voltage of the converter is defined as T and -it and Jt-J..9ll. and .. ,, ... QW m u, it): -; i., itwt.i5.iS where T is the period of change of the input voltage Q QJ (t). The first term in equation (5) is equal to zero, since the mean value of the variable input voltage (Vc t) is zero. Therefore, Thus, the output voltage of the low-pass filter 4, which is the output voltage of the entire converter, is proportional to the rms value of the input voltage. It does not depend on the bias voltage of the operational amplifier, on the basis of which the adder 5 is built. The unbalance amplifier 3 amplifies the alternating voltage in a wide frequency range, and the adder 5 sums the voltage of the fair current. Broadband operational amplifiers have a ten-fold higher displacement voltage than operational amplifiers designed to handle a DC voltage. Therefore, a pre-mounted device is characterized by an increased conversion accuracy.

Claims (1)

LINEAR CONVERTER OF THE CURRENT VALUE OF VARIABLE VOLTAGE by ed. No. 741167, characterized in that, in order to increase the conversion accuracy, an adder is introduced into the circuit between the output terminal of the low-pass filter and the drain of the first field-effect transistor, the other input terminal of which is connected to the source of the first field-effect transistor.