SU1430898A1 - Linear converter of mean-square voltage value - Google Patents

Abstract

The invention relates to the field of electrical measuring equipment and can be used to convert a constant or alternating voltage into a constant voltage. The purpose of the invention is to simplify the device by eliminating two field effect transistors. The converter contains quadrants made on field-effect transistors 1, 2, a DC amplifier 3, a polarity limiter 4, resistors 5, 7, and 8 and a capacitor 6. In the device for obtaining a given conversion accuracy, linear components are compensated, flowed through field effect transistors 1 and 2 currents. Only two field effect transistors are used. Additionally, the need to match the field-effect transistor pairs is eliminated, which simplifies the process of tuning the converter. 1 il. (About iMii. (KU 00

Description

The invention relates to electrical measuring equipment and can be used to convert DC or AC voltages, as well as their Sum, to DC voltage in terms of the root-mean-square value.

The purpose of the invention is to simplify the device by eliminating part of the field-effect transistors.

The drawing shows the block diagram of the Converter.

The converter contains two quadrants, made on field-effect transistors I and Zj, DC amplifier 3, limiter 4 polarity, resistor 5, capacitor 6, and also resistors 7 and 8. The sources of field-effect transistors 1 and 2 are connected to their own gates. The drain of transistor 1 is connected to the input bus (not shown), the source of the transistor. 2 output bus (not shown) and through the limiter 4 polarity with the output of the DC amplifier 3. The non-inverting input of the DC amplifier 3 is connected to the source of transistor 1, the drain of transistor 2 and the first pin of resistor Sj whose second output is connected to the common power cable and the output of the DC amplifier 3 is connected to its inverter 1 through the capacitor 6. The first output of resistor 7 It is connected to the input bus, its second terminal is connected to the inverting input of the DC amplifier 3 and to the first terminal of the resistor B, the second terminal of which is connected to the output bus.

The converter works as follows

When a measured voltage Uj is supplied to the input bus through a field-effect transistor 1 and a resistor 5, the current ToK;

I, - () () 2.bi, causing a voltage drop across and on the resistor 5. In the above expression, a and b are constants associated with the parameters of the field-dependent transistors; GS, - channel conductivity and - jan jen cut-off of the field-effect transistor, / 2Uj (,), Therefore, the inclusion of the field-effect transistor t is such that the sign of the quadratic component of the current -I is positive

At the same time, the current through the resistor 7 is equal

five

I, () / R ,.

Accordingly, the current 1 flowing through the field-effect transistor 2 and the resistor 5 caused by the output voltage of the same polarity is equal to

(U6 ,, - U) a, - (Ug ,, - U) ba.

In this case, the field-effect transistor 2 is turned on in such a way that the quadratic component of the 0 current of the current 1 has a sign opposite to the quadratic component of the current I ,. In turn, the current Ig flowing through the resistor 8 is equal to

(and-Ubykh) / Kk.

Thus, at the non-inverting input of the DC amplifier 3, a voltage is generated due to the flow of currents II and IJ through a resistor 5 equal to () R and the same voltage is formed at its inverting input, but due to the flow of currents 17 and Ig through the resistors 7 and 8, equal to

These voltages are subtracted from one another by amplifier 3, and their difference is amplified by K, where Kj is the gain of the open amplifier 3. Due to the presence of condensate,

6 through the limiter 4 polarities on the output bus of the converter enters the average value of the amplified voltage difference acting on the inputs of the amplifier 3. stress

0

five

0

five

If,, and if the components of the current 1 of the same sign are linear and quadratic, an undesirable positive feedback is formed. Thus, the output voltage of the converter is described by the expression

and "x. C (ii + i,) R5- (7R7-isR8) -K3

where the bar means averaging.

Let us substitute the equations for currents I, I, I, Ig into the last expression, taking into account the fact that the parameters of field-effect transistors, made on the same substrate, according to the same technology and operating under the same conditions, are equal to

, but

55 also that, we get

and;;;; (, + i ujt siG-i |, x -2U (U, -U ,,,). R.Kj,

where does that

Since the transmission coefficient Kj 5 is open1 about amplifier 3 has a value greater than 10, and G, is the ratio of the saturation current 1 to the cut-off voltage Uj of the field-effect transistor: / Uje and Ohm, i.e. RGp / Uj rl, S7D "0.10

we can assume that, 0 with an error of no more than 0.001%. Then the output voltage of the converter is rav

and

CK5

Those. RMS 5

tical value of U. input voltage and.

Thus, if in the prototype, bridging of field-effect transistors is used to obtain the same conversion accuracy, providing compensation for the linear components of the currents flowing through them, then the proposed converter has a compensation value that is achieved at half the number of field-effect transistors, which allows to simplify converter. This additionally eliminates the need to select pairs of transistors, simplifies the process of setting up the converter.

Claims (1)

Invention Formula The linear converter of the RMS voltage, containing two quadrs, made on field-effect transistors, the sources of which are connected to the gates, the drain of the first field-effect transistor is connected to the input bus-, the source of the second is connected to the output bus and simultaneously through the polarity limiter is connected to the output of the amplifier DC, to the non-inverting input of which the source of the first field-effect transistor, the port of the second field-effect transistor and the first terminal of the first resistor, the second terminal of which are connected It is connected to the common bus, and the output of the DC amplifier is connected via a capacitor to its inverting input, which is due to the fact that, in order to simplify the linear converter, the second and third resistors are additionally added, and the first output of the second resistor is connected to the input bus, its second output is connected to the inverting input of the DC amplifier and simultaneously connected to the first output of the third resistor, the second output of which is connected to the output bus.