CS227192B1 - Circuit for transmitting bigger of two signals - Google Patents

Description

The invention relates to a circuit for transmitting the larger of two signals. This is a circuit whose output is constantly the larger of the two input variable signals.

So far, two circuits are known to solve this problem. The principle of the first known type is that each of the circuit inputs is connected to the anode of one diode and one end of the resistor is connected to the cathode junction of these diodes, the other end of which is connected to a potential lower than the minimum input voltage. The output voltage is the voltage at this resistor and is equal to the greater of the two input voltages minus the diode voltage drop. The main drawback of this type of circuit is the dependence of the voltage drop on the open diode on the size of the input voltage. This dependence is usually eliminated by supplying diodes from a constant current source. Another drawback is the temperature dependence of the voltage drop on the diode. Its influence is usually reduced by temperature compensation. Sometimes a non-zero outlet may also be a malfunction, which is solved by the inclusion of a decoupling amplifier. Generally speaking, this circuit in its simple form will only satisfy very low demands on accuracy. Remedying its shortcomings is possible, but the result is a rather complex involvement.

The principle of the second type of circuits is that both input signals are routed to a controlled electronic switch which switches one of these input signals to output, depending on the output state of the comparator, which compares the mutual magnitude of the two input signals. This circuit works precisely, the disadvantage of which is the greater circumferential complexity due to the larger number of components used. As a rule, a level converter must be connected to the comparator output, which converts the comparator output level to a level suitable for controlling the electronic switch. If there is a non-zero output resistance, it is necessary to connect a decoupling amplifier to the input.

The above-mentioned drawbacks are eliminated by the larger signal transmission circuit of the two signals according to the invention, consisting of two operational amplifiers, two diodes and four resistors. Its essence is that one input terminal is connected to the non-inverting inputs of both operational amplifiers and the other input terminal is connected via a resistor to the inverting input of one operational amplifier. On the input of this operational amplifier is connected cathode diode, whose anode is connected to the output of this ope227192

227A92 rational amplifier q. secondly to the cathode ýlajš / ^A $ ^{O (? <ét0 "d} W ^e Cw i ^é $ W * ^and via a feedback resistor, with maple, tujícýn vstupeip first operational amplifier and secondly přes'pdppr \ with a second input invbrtváífíip Opera $ p The output of this expensive opamp, which is also the output of the whole circuit, is connected via a feedback resistor to the inverting input of the opamp. The product of the feedback resistances is equal to the product of the resistor sizes connected. to inverting inputs of these trademarks.

The advantage of this is that, with high accuracy, the number of elements required for its realization is limited. In addition, the output resistance of the circuit is negligible and the input resistance of the input formed by the junction of the non-inverting inputs of the oper. The amplifiers are large.

An example of wiring is shown in the attached drawing.

The circuit consists of two operational amplifiers 1, 2, two diodes 3, 4 and four resistors 5, 6, 7, 8, where the resistors B, 8 are feedback. One input terminal of the circuit is connected to the inverting input of the operational; esiloygč $ J ..> ² · AP instill connections over $ 5 jinyejrt ^ ^ PEM jícýn YPT first operations in Amp # # marking 1. LYP tepto inverting input of the first supports ^ čpíjho the cathode of the diode 3 is connected to the output of the first operational amplifier 1 and to the cathode of the diode 4. The anode of the diode 4 is connected via a feedback resistor 6 with inverting input of the second operational amplifier 1 and over the resistor. the inyeft input of the operational amplifier 2; a feedback resistor 8 is connected between the output and the inverting input of the dump operational amplifier 2. The output of this operational amplifier 2 is the output of the entire circuit. For resistors 5, 7 and feedback resistors 6, 8, the sizes of which are pp f pě Rs, Ri, Re and Ri apply

RaRe = R7R5

The function of this circuit is as follows. If U _vSt i is greater than U _vs i2, diode 3 is not energized, it is closed, and pipda 4 is conducting, y is open.

AT.

vst.

R, p.

í Rs Rs

R «Rg> f Ra Ra

P, R 5 's

If the condition is met, ReRe = R7R5 or

ReRe

R7R5

1, then it will rise - U _vst l.

In case U _vst i is smaller than U _vst z, diode 4 is closed and current flows through diode 3. For output voltage then:

out

Re

R7 + R6

UvstZ (1 +

R8

R7 + R6) U _input 2, ie: U-out _in st2>

The advantage of the circuit is its high accuracy of function with a small number of components used. It is also possible to use a double operational amplifier.

The circuit can be used not only in all wiring where it is required to monitor a larger signal, but also in limiting circuits; if any input of this circuit is connected to constant voltage U _o and the second input is supplied with variable input voltage U _vst , the circuit will behave as a precise limiting circuit with the characteristic for U _vst u U _o Uout = U _vst for

U _vst <U _o holds Uout = U _o

Claims (1)

SUBJECT A circuit for transmitting a larger of two sinals consisting of two opamps, two diodes and four resistors, characterized in that one input terminal is connected to the non-inverting inputs of the operational amplifiers (1j and (2) and the other input terminal is connected via a resistor ( 5j with an inverting input of the first operational amplifier (lj) to which the cathode of the diode (3) is connected, the anode of which is connected to the output of the first operational amplifier (lj) and the cathode 6J with an inverting input of the first operational amplifier (1j) and through a resistor (7) with an inverting input of the second operational amplifier (2), the output of which is the output of the entire circuit and the inverting input is connected with a second feedback resistor (8); the product of the magnitude of the feedback resistances (6) and (8J) is equal to the product of the magnitude of the resistances (5j and (7)).