DE4001092C1 - Current-voltage converter without auxiliary power supply - has bridge circuit with two parallel branches, one with fixed voltage divider, other with variable - Google Patents

Abstract

The current/voltage converter has an electronic circuit for one of the input currents to be converted and from which, on the two voltage outputs (9), a voltage (Ua) proportional to the input current (I) can be obtained. The circuit is of the bridge type with two parallel branches (1,2), the first being a fixed voltage divider (4) and the second a regulated voltage divider (5). The second consists of a fixed resistance (R3) and a regulating package (RE) which has no auxiliary power supply and which regulates the part-current through the voltage divider (5) to a fixed ratio of the part current through the other voltage divider (4) and so to a fixed ratio of the input current (I), independent of the load on the output. USE/ADVANTAGE - Improved accuracy of conversion.

Description

The invention relates to a current / voltage converter without auxiliary power supply supply with the features specified in the preamble of claim 1.

Current / voltage converter without auxiliary power supply, such as, for example from the company publication of the applicant "DC transformers without Auxiliary power types 41/42 ", August 1988, p. 5, circuit example 5, are known usually an electronic circuit with an ohmic resistor on which an input current to be converted flows. The two connection points of this ohmic resistance form the voltage output tapped an output voltage proportional to the input current can be. This makes it a particularly simple one Current / voltage converter, which, however, has the disadvantage that the on voltage dropped due to a current load of the voltage off can be falsified by a subsequent circuit. This usual Circuitry is therefore only for very high with high accuracy requirements ohmic follow-up circuits suitable.

From the journal "Electronics", 1970, Issue 12, p. 410 is a Current / voltage converter with an electronic circuit known after Kind of a bridge circuit is constructed with two parallel branches. These Parallel branches are fixed voltage dividers, the center taps of which Inputs of an operational amplifier are connected. At the exit of the as OP amplifier acting as a voltage regulator is one for input current of the current / voltage converter proportional voltage can be tapped is essentially independent of a burden flow. However, for the described current / voltage converter an auxiliary power supply for the Operational amplifier necessary.

The invention has for its object a To develop current / voltage converter without auxiliary power supply in such a way that a  high-precision current / voltage conversion even when the current is loaded Voltage output (hereinafter referred to as "burden current") by a less high-impedance sequential switching is made possible.

The solution to this problem is in the characteristic features of the contractor pronounced 1. Accordingly, the circuit is like a bridge circuit with two parallel branches, the first of which is a fixed chip voltage divider and the second is a regulated voltage divider. The latter be consists of a fixed resistor and an auxiliary power-free control module, the partial current through the regulated voltage divider to a fixed Ratio value to the partial flow through the fixed voltage divider and thus on regulates a fixed ratio to the input current to be converted. Here the output voltage between the infeed point of the Fixed voltage divider and the center tap of the regulated voltage divider tapped. The purpose of the invention is achieved in that Regulation of the partial flows through the two parallel branches of the bridge circuit to a fixed ratio to each other and thus to a fixed ratio value of the respective partial flows to the input current to be converted output voltage proportional to this regardless of a load on the Voltage output through a burden current. Through this independence Ability is a highly precise, since load-independent change of the one current into a corresponding output voltage possible. Because of that no auxiliary power supply of the circuit is necessary, this can be particularly be used advantageously in application areas for which the one relevant explosion protection regulations apply.

The rule block can perform its rule task specified in claim 1 simplest case in that he the center taps of the two Span regulates the voltage divider of the bridge circuit to the same potential. He's about that an electroless connection line with the center tap of the fixed voltage divider connected (claim 2). In connection with the measure that Regulate center taps of the two voltage dividers to the same potential, and the feature specified in claim 1 that the output voltage between between the supply point of the fixed voltage divider and the center tap of the regulated voltage divider is tapped, the special trick is circuit according to the invention clearly. The one with a burden flow up to one dimensioning-dependent limit loadable output voltage namely not on the supply-side fixed resistance of the fixed voltage part  tapped - what the simple resistance of the usual Current / voltage converter known, faulty voltage reduction be would act - but as a corresponding tension value between the Infeed point of the fixed voltage divider and the middle handle of the gere apply voltage divider. As a result of the regulation, this voltage corresponds to Center taps of the two voltage dividers to the same potential precisely the the voltage at the fixed resistor proportional to the input current to be converted the fixed voltage divider, which is not burdened by the burden current.

In the case of a very small input current to be converted, this can be done in the control building stone-lying voltage - that due to the lack of auxiliary energy supply is necessary for its operation - become too small for its function. Des half becomes according to claim 3, the feed point of the fixed voltage divider a component connected in series that provides an additional independent of current generated voltage drop. For example, this can be a Diode in the direction of flow, a Zener diode or a voltage reference element act without special accuracy requirements. This changes the desired fixed current / voltage conversion nothing.

A special embodiment for the control module is in claim 4 given. It is therefore an operational amplifier, the two inputs in the appropriate polarity each at a center tap of the both voltage dividers are connected. In addition, its a provider Connection of correct polarity also on the center tap of the regulated Voltage divider connected. The other supply connection is with the Infeed point of the input current connected to the overall circuit. The output of the operational amplifier is connected to one of its supply lines conclusions switched. With this circuit design, the operations complement amplifies its supply quiescent current through its output current to that depending on the burden current required control current to the at the beginning of the partial current ratios in the voltage dividers ensure. The operational amplifier must have an input common mode modulation capability up to at least one of its supply connections Show potential.

It is pointed out that from the publication "Nacrichtentechnische Zeitung ", 1974, Issue 3, Picture 5 with the associated description is known at  to use a ΔU converter operational amplifier where a Signal current is forwarded via the OP operating voltage connections.

The embodiment according to claim 4 is unchanged on an input current changed polarity, i.e. on direct current or wavy current without zero crossings limited. To avoid this disadvantage, according to claim 5 is pre see that the control block from the operational amplifier and its Supply connections upstream bridge rectifier sets is. This makes the operational amplifier independent of the direction of the input current to be converted always with voltage of the correct polarity provided.

Through the development of the current / voltage converter according to the invention According to claim 6, an operational amplifier can be used for the control module whose inputs are not up to at least one of its Supply connection potentials may be controlled. The additional, the voltage output and thus the burden connected in parallel Fixed voltage divider shifts the operational amplifier input potential into a middle range between the supply potentials.  

The specified in claim 7, the output of the operational amplifier downstream output resistance brings u. a. the advantage that the Aus output voltage of the operational amplifier in the middle range between NEN supply potential is shifted. That's the only way many work Types of common operational amplifiers flawlessly. In addition, the Output resistance thermally and can the operational amplifier have a stabilizing effect against self-excited vibrations, especially in cooperation with other stabilization components.

Further features, details and advantages of the invention are the following description can be seen in the embodiments of the Current / voltage converter explained in more detail with reference to the figures will. It shows

Fig. 1 is a generalized circuit diagram of the current / voltage converter according to the invention and

Fig. 2-5 circuit diagrams of various embodiments of the current / voltage converter.

Referring to Fig. 1, the general structure of the current / voltage converter of the invention is first explained. The overall circuit is constructed in the manner of a bridge circuit with two parallel branches 1, 2 . Starting from the feed point 3 of the input current I to be converted, the first parallel branch 1 is a fixed voltage divider 4 , consisting of the two ohmic fixed resistors R 1 , R 2 . The second parallel branch 2 is constructed as a regulated voltage divider 5 from the supply point-side control module RE and the ohmic fixed resistor R 3 . At node 6 , the two parallel branches 1, 2 converge.

Between the upper feed point 7 of the fixed voltage divider 4 and the center tap 10 of the regulated voltage divider 5 , the voltage output 9, which is proportional to the input current I to be converted _{, is} tapped via the voltage output 9 .

The auxiliary power-free control module RE is connected via a substantially currentless connecting line L to the center tap 8 of the fixed voltage divider 4 . The control module RE is constructed in such a way that it regulates the two center taps 8, 10 of the two voltage dividers 4, 5 to the same potential. Characterized who the the voltages on the two fixed resistors R 1 and R 3 kept the same size, which inevitably causes the partial currents through the fixed resistor R 3 and the fixed voltage divider 4 to each other and thus to a fixed ratio to the input current I to be converted to adjust. Thus, regardless of a possible load resistance RB (burden) at voltage output 9, there is always an output voltage U _a that is precisely representative of the input current I.

From Fig. 1 it can also be seen that between the feed point 7 of the fixed voltage divider 4 and the feed point 3 of the overall circuit, a component BU can be installed, which generates a current-independent voltage drop. This voltage drop ensures that the RE control module, which is free of auxiliary power, functions properly even with small input currents I.

In Fig. 2 the circuit diagram of a current / voltage converter for an input current I to be converted unchanged polarity (direct current or ripple current without zero crossings) is shown. The control module RE is designed as an operational amplifier OP. Its non-inverting input is connected to the center tap 8 of the fixed voltage divider 4 via the connecting line L. Its inverting input, its output and its negative supply connection are at the center tap 10 of the regulated voltage divider 5 formed by the operational amplifier OP in connection with the fixed resistor R 3 . The positive supply connection is connected to the feed point 3 of the overall circuit. In analogy to the general circuit shown in Fig. 1, the operational amplifier OP regulates its own current consumption so that the current I to be converted, regardless of its size and the size of the burden resistor RB, is always in an unchanged fractional ratio in the two voltage dividers 4, 5th divides. This is done by regulating to a voltage difference of 0 between the two center taps 8, 10 of the voltage divider 4, 5 .

As is clear from the calculation associated with FIG. 2, the output voltage U _a and the input current I have the following relationship, in which the burden resistor RB does not appear as a variable variable:

U _a = I · R 2 / (1 + R 1 / R 3 )

The component BU according to FIG. 1 is implemented in the exemplary embodiments according to FIGS. 2-5 from one or two oppositely directed Zener diodes Z.

Furthermore, the output of the operational amplifier OP is an output resistor stood downstream RV, which is the output voltage of the operational amplifier kers OP in the middle range between its two supply potentials brings. This output resistance also relieves the operational amplifier OP thermal and increased u. U. the stability of the circuit against self-excited Vibrations.

In the dimensioning of the resistors R 1 , R 2 and R 3 , a compromise must be found between the requirement for the highest possible output current carrying capacity - which requires a high-resistance resistor R 1 and a low-resistance resistor R 3 - and the requirement for a ge wrestle influence of the operational amplifier offset voltage. The latter requires that it a with respect to the resistance R relatively high impedance 1 Wi resistor R 3, which at the same time the favorable effect is that the error influences of R 1 and R 3 are negligible by resistance tolerances and drift and essentially only the resistance R 2 is precision determining. Furthermore, the current source must be weighed between the requirement for the highest possible output voltage U _a at a given maximum voltage swing and the requirement for a low offset voltage influence. The former means a high factor R 2 / R 1 , the latter the opposite. When choosing a high factor R 3 / R 1 , however, the offset influence of the factor R 2 / R 1 is low, so that a higher factor R 2 / R 1 may then be selected.

The circuits shown in FIGS. 3-5 of further developed forms of the current / voltage converter according to the invention are based on the circuit according to FIG. 2. Therefore, only the additions or changes to the circuit according to FIG. 2 are explained in more detail.

Fig. 3 shows a circuit in which an operational amplifier OP can be used, the inputs of its two supply terminal potentials are not allowed to be driven to at least one. For this purpose, an additional voltage divider 11 consisting of the fixed resistors R 4 , R 5 is installed parallel to the voltage output 9 , to the center tap 12 of which the inverting input of the operational amplifier OP is connected. This voltage divider 11, which is parallel to the burden resistor RB, shifts the operational amplifier input potential into a middle range between the supply potentials. The output voltage U _a is then not equal to the voltage across the resistor R 2 , but rather by the fixed factor (R 4 + R 5 ) / R 5 .

The circuit of FIG. 4 is to be used when the is an alternating current or a current wave with zero crossings to be converted current I. In this case, the control module RE is composed of the operational amplifier OP and a bridge rectifier G. The operational amplifier OP is connected with its non-inverting input to the center tap 8 of the fixed voltage divider 4 . With its inverting input, the operational amplifier OP is connected to the center tap 10 of the regulated voltage divider 5 formed by it in connection with the bridge rectifier G and the fixed resistor R 3 . Its output is connected to the negative supply connection. The bridge rectifier G is connected with its bridges infeed points 13 to the infeed point 3 of the input current I or the center tap 10 of the regulated voltage divider 5 . The bridge tapping points 14 are connected to the positive and negative supply connection of the operational amplifier OP, the output resistor RV additionally being connected between the output of the operational amplifier OP and its negative supply connection. Due to the circuit formation described above, the operational amplifier OP is always supplied with voltage of the correct polarity regardless of the direction of the input current I to be converted.

In the circuit of Fig. 5 is in deviation from the circuits shown in Fig. 3 and 4, the inverting input of the operational amplifier OP to the center 8 of the fixed voltage divider 4 and the non-inverting input connected to the center tap 12 of the voltage divider 10 is connected. Accordingly, the output of the operational amplifier is connected to the positive supply connection via the output resistor RV.
Reference numerals

1 parallel branch
2 parallel branches
3 entry point
4 fixed voltage dividers
5 regulated voltage dividers
6 node
7 entry point
8 center tap
9 voltage output
10 center tap
11 voltage dividers
12 center tap
13 bridge feed point
14 bridge tap point

I input current
U _a output voltage
R 1 , R 2 , R 3 , R 4 , R 5 Ohmic fixed resistance
RV output resistance
RE rule block
L connecting line
RB load resistance
BU component
OP operational amplifier
Z zener diode

Claims (9)

1. current / voltage converter without auxiliary power supply with an electronic circuit,

• - Flows through an input current (I) to be converted and
• an output voltage (U _a ) proportional to the input current (I) is tapped at two circuit points forming the voltage output ( 9 ),

characterized in that the circuit is constructed in the manner of a bridge circuit with two parallel branches ( 1, 2 ),

• - The first of a fixed voltage divider ( 4 ) and
• - The second is a regulated voltage divider ( 5 ) from a fixed resistor (R 3 ) and an auxiliary power-free control module (RE), which is the partial current through the regulated voltage divider ( 5 ) to a fixed ratio to the partial current through the fixed voltage divider ( 4 ) and thus regulates to a fixed ratio to the input current (I), the output voltage (U _a )
  • - Tapped between the feed point ( 7 ) of the fixed voltage divider ( 4 ) and the center tap ( 10 ) of the regulated voltage divider ( 5 ) and
  • - by regulating the partial currents through the two parallel branches ( 1, 2 ) to a fixed ratio regardless of a load on the voltage output ( 9 ) by a burden current.

2. Current / voltage converter according to claim 1, characterized in that the control module (RE) via a currentless connecting line (L) with the center tap ( 8 ) of the fixed voltage divider ( 4 ) and the center taps ( 8, 10 ) of the two voltage dividers ( 4, 5 ) regulates to the same potential. 3. Current / voltage converter according to claim 1 or 2, characterized in that the feed point ( 7 ) of the fixed voltage divider ( 4 ) in series with a current-independent voltage drop generating component (BU), in particular a diode in the direction of flow, a Zener diode (Z) or a voltage reference element is connected upstream. 4. Current / voltage converter according to one of the preceding claims, characterized in that the control module (RE) consists of an operational amplifier (OP), the

• - With its one input on the center tap ( 8 ) of the fixed voltage divider ( 4 ),
• - With its other input and its one supply connection on the center tap ( 10 ) of the regulated voltage divider ( 5 ) formed by it in connection with the fixed resistor (R 3 ),
• - With its other supply connection at the feed point ( 3 ) of the input current (I) and
• - With its output on one of its two supply connections

connected. 5. Current / voltage converter according to one of claims 1-3, characterized in that the control module (RE) has an operational amplifier (OP) and one of its supply connections upstream bridge rectifier (G), wherein

• - the operational amplifier (OP),
  • - With its one input on the center tap ( 8 ) of the fixed voltage divider ( 4 ),
  • - With its other input on the center tap ( 10 ) of it in connection with the bridge rectifier (G) and the fixed resistor (R 3 ) ge formed, regulated voltage divider ( 5 ) and
  • - With its output connected to a supply connection and
• - the bridge rectifier (G)
  • - With its bridge feed points ( 13 ) with the feed point ( 3 ) of the input current (I) or the center tap ( 10 ) of the regulated voltage divider ( 5 ) and
  • - With its bridge tapping points ( 14 ) is connected to the supply connections of the operational amplifier (OP).

6. Current / voltage converter according to claim 4 or 5, characterized in that the one input of the operational amplifier (OP) not directly with the center tap ( 10 ) of the regulated voltage divider ( 5 ), but with the center tap ( 12 ) one of the voltage output ( 9 ) parallel fixed voltage divider ( 11 ) is connected. 7. Current / voltage converter according to one of claims 4-6, characterized, that the output of the operational amplifier (OP) has an output resistor (RV) is connected downstream.