CN212305301U - PWM isolation control output 4-20mA circuit - Google Patents

Abstract

The utility model provides a PWM isolation control exports 4-20mA circuit, include: the PWM signal isolation circuit, the standardized conditioning circuit and the transmitting output circuit; the output end of the PWM signal isolation circuit is connected with the input end of the standardized conditioning circuit, and the output end of the standardized conditioning circuit is connected with the input end of the transmitting output circuit; the PWM signal isolation circuit includes: resistance R₁And a high-speed optical coupler U₁(ii) a The standardized conditioning circuit includes: single-pole double-throw analog switch U₂Capacitor C₃Capacitor C₄Capacitor C₅Resistance R₃Resistance R₄And a resistance R₅(ii) a The utility model discloses a high-speed opto-coupler realizes that the opto-coupler keeps apart, makes transmitting signal end and electricityThe paths are not interfered with each other, signal distortion is prevented, signals are subjected to standardized reduction through the standardized conditioning circuit, high-precision current signals are transmitted and output, and the high-precision current signal transmitting and outputting device is more practical.

Description

PWM isolation control output 4-20mA circuit

Technical Field

The utility model relates to a signal processing field especially relates to a PWM isolation control exports 4-20mA circuit.

Background

In industrial applications, it is generally necessary to measure physical quantities such as temperature, pressure, flow rate and liquid level, and these quantities are usually converted into standard analog electrical signals before they can be transmitted to a control room or a display device several hundred meters away. The standard analog electric signal most widely adopted in the industry is to transmit analog quantity by using 4-20mA direct current. The reason for adopting the current signal is that the interference is not easy to happen, the internal resistance of the current source is infinite, the accuracy is not influenced when the wire resistor is connected in series in the loop, and hundreds of meters can be transmitted on the common twisted pair wire. Most of the existing 4-20mA analog quantity transmission circuits are not electrically isolated, or the structures of the electrically isolated circuits are relatively complex, the transmission precision is not high enough, the anti-interference performance is poor, the safety is poor, so that the waveforms of PWM signals after electrical isolation are distorted, and the application is unreliable.

SUMMERY OF THE UTILITY MODEL

The utility model provides a PWM isolation control output 4-20mA circuit to overcome above-mentioned technical problem.

The utility model provides a PWM isolation control exports 4-20mA circuit, include: the PWM signal isolation circuit, the standardized conditioning circuit and the transmitting output circuit;

the output end of the PWM signal isolation circuit is connected with the input end of the standardized conditioning circuit, and the output end of the standardized conditioning circuit is connected with the input end of the transmitting output circuit;

the PWM signal isolation circuit includes: resistance R₁And a high-speed optical coupler U₁；

The standardized conditioning circuit includes: single-pole double-throw analog switch U₂Capacitor C₃Capacitor C₄Capacitor C₅Resistance R₃Resistance R₄And a resistance R₅；

The resistor R₁And the high-speed optical coupler U₁Is connected with the emitting end of the high-speed optical coupler U₁The receiving ends of the analog switches are respectively connected with the single-pole double-throw analog switch U₂Pin S is connected with pin VCC; the capacitor C₃And a capacitor C₄Parallel single-pole double-throw analog switch U₂Pin B of₂And the capacitor C₃And a capacitor C₄Is connected with a single-pole double-throw analog switch U₂Pin B of₁GND and the capacitor C₃And a capacitor C₄The connection points b are connected and grounded; the resistor R₅Is connected with the single-pole double-throw analog switch U₂Pin a and the resistor R₃Between one end, the resistor R₃The other end of the output end of the transmitting circuit is connected with the input end of the transmitting output circuit; the resistor R₄Is connected with the single-pole double-throw analog switch U₂Between the pin S and the ground point; the capacitor C₅Is connected to the resistor R₃And a resistance R₄And a ground point.

Further, the transmission output circuit includes: current loop transmitter chip U₃And a triode Q₁；

Current loop transmitter chip U₃Pin VREG and the single-pole double-throw analog switch U₂The pins VCC are connected; the pin VREF is connected with the connection point a; pin IIN and the resistor R₃The other end is connected; pin IRET is connected to ground; pin V + and said triode Q₁The collector electrodes are connected; pin B and said triode Q₁The base electrodes are connected; pin E and said triode Q₁The emitting electrodes are connected; pin IO is a current output pin.

Further, still include: capacitor C₆And a capacitor C₇；

The capacitor C₆And a capacitor C₇In parallel, the capacitor C₆And a capacitor C₇A connection point of the current loop transmitter chip U₃Pin VREG of (a) is connected and the other connection point is grounded.

Further, still include: bidirectional TVS tube D₁And bidirectional TVS tube D₂；

The bidirectional TVS tube D₁Is connected to the triode Q₁Collector and the current loop transmitter chip U₃Between pins IO; the bidirectional TVS tube D₂Connected to the current loop transmitter chip U₃Between pin IO and ground.

Further, still include: capacitor C₁And a capacitor C₂；

The capacitor C₁And the bidirectional TVS tube D₁In parallel, the capacitor C₂And the bidirectional TVS tube D₂And (4) connecting in parallel.

The utility model discloses a set up high-speed opto-coupler and realize that the opto-coupler keeps apart, make transmission signal end and circuit mutual noninterference, prevent signal distortion, and through setting up standardized conditioning circuit carries out standardized reduction with the signal, realizes high accuracy current signal transmission output, makes it more have the practicality.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive labor.

FIG. 1 is a schematic diagram of the overall circuit structure of the present invention;

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

The utility model provides a PWM isolation control output 4-20mA circuit, as shown in figure 1, the utility model discloses whole circuit structure schematic diagram, include: the PWM signal isolation circuit, the standardized conditioning circuit and the transmitting output circuit;

the output end of the PWM signal isolation circuit is connected with the input end of the standardized conditioning circuit, and the output end of the standardized conditioning circuit is connected with the input end of the transmitting output circuit;

the PWM signal isolation circuit includes: resistance R₁And a high-speed optical coupler U₁；

The standardized conditioning circuit includes: single-pole double-throw analog switch U₂Capacitor C₃Capacitor C₄Capacitor C₅Resistance R₃Resistance R₄And a resistance R₅；

The resistor R₁And the high-speed optical coupler U₁Is connected with the emitting end of the high-speed optical coupler U₁The receiving ends of the analog switches are respectively connected with the single-pole double-throw analog switch U₂Pin S is connected with pin VCC; the capacitor C₃And a capacitor C₄Parallel single-pole double-throw analog switch U₂Pin B of₂And the capacitor C₃And a capacitor C₄Is connected with a single-pole double-throw analog switch U₂Pin B of₁GND and the capacitor C₃And a capacitor C₄The connection points b are connected and grounded; the resistor R₅Is connected with the single-pole double-throw analog switch U₂Pin a and the resistor R₃Between one end, the resistor R₃The other end of the output end of the transmitting circuit is connected with the input end of the transmitting output circuit; the resistor R₄Is connected with the single-pole double-throw analog switch U₂Between the pin S and the ground point; the capacitor C₅Is connected to the resistor R₃And a resistance R₄And a ground point.

Specifically, after the on-site PWM signal is optically coupled and isolated by the PWM signal isolation circuit, the PWM signal is distorted, and the standardized conditioning circuit is used for standardized reduction processing, namely, a single-pole double-throw analog switch U is used₂Carry out reduction, single-pole double-throw analog switch U₂Is preferably 74LVC1G3157, and the capacitor C₃Has a parameter of 10 muF/16V, the capacitance C₄The parameter (d) is 0.1 muF/25V; after the isolation, the PWM signal is used as a selection signal of the analog switch, the high level selects 2.5V of the power reference, the low level selects 0V of the power ground, the output end of the analog switch can generate the standard PWM signal of 0 and 2.5V, thereby being capable of ensuring thatHigh accuracy of the PWM signal is guaranteed; the 4-20mA transmitting output circuit converts the standardized PWM signal into a 4-20mA current loop signal.

Further, the transmission output circuit includes: current loop transmitter chip U₃And a transistor Q1;

current loop transmitter chip U₃Pin VREG and the single-pole double-throw analog switch U₂The pins VCC are connected; the pin VREF is connected with the connection point a; pin IIN and the resistor R₃The other end is connected; pin IRET is connected to ground; pin V + and said triode Q₁The collector electrodes are connected; pin B and said triode Q₁The base electrodes are connected; pin E and said triode Q₁The emitting electrodes are connected; pin IO is a current output pin.

Specifically, the current loop transmitter chip U₃Preferably XTR115U, which sends the received normalized signal out and through the transistor Q₁And carrying out amplification treatment.

Further, still include: capacitor C₆And a capacitor C₇；

The capacitor C₆And a capacitor C₇In parallel, the capacitor C₆And a capacitor C₇A connection point of the current loop transmitter chip U₃Pin VREG of (a) is connected and the other connection point is grounded. The capacitor C₆And a capacitor C₇Form a decoupling capacitor to a single-pole double-throw analog switch U₂The processed signals are further decoupled.

Further, still include: bidirectional TVS tube D₁And bidirectional TVS tube D₂；

The bidirectional TVS tube D₁Is connected to the triode Q₁Collector and the current loop transmitter chip U₃Between pins IO; the bidirectional TVS tube D₂Connected to the current loop transmitter chip U₃Between pin IO and ground. Bidirectional TVS tube D₁And bidirectional TVS tube D₂Form a TVS transient suppression circuit to realize the absorption of peak interference voltage

Further, still include:capacitor C₁And a capacitor C₂；

The capacitor C₁And the bidirectional TVS tube D₁In parallel, the capacitor C₂And the bidirectional TVS tube D₂And (4) connecting in parallel. Capacitor C₁And a capacitor C₂The arrangement of (3) suppresses differential mode interference on the far-end signal.

Compared with the prior art, the circuit has the advantages of simple overall structure and control mode, high transmission precision, easy integration into the circuit of an industrial controller, no waveform distortion and high precision of the PWM signal after electrical isolation after standardized processing, and high circuit safety and strong anti-interference performance by adopting output transient suppression protection.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention.

Claims (5)

1. A PWM isolation control output 4-20mA circuit, comprising: the PWM signal isolation circuit, the standardized conditioning circuit and the transmitting output circuit;

the output end of the PWM signal isolation circuit is connected with the input end of the standardized conditioning circuit, and the output end of the standardized conditioning circuit is connected with the input end of the transmitting output circuit;

the PWM signal isolation circuit includes: resistance R₁And a high-speed optical coupler U₁；

The standardized conditioning circuit includes: single-pole double-throw analog switch U₂Capacitor C₃Capacitor C₄Capacitor C₅Resistance R₃Resistance R₄And a resistance R₅；

The resistor R₁And the high-speed lightCoupler U₁Is connected with the emitting end of the high-speed optical coupler U₁The receiving ends of the analog switches are respectively connected with the single-pole double-throw analog switch U₂Pin S is connected with pin VCC; the capacitor C₃And a capacitor C₄Parallel single-pole double-throw analog switch U₂Pin B of₂And the capacitor C₃And a capacitor C₄Is connected with a single-pole double-throw analog switch U₂Pin B of₁GND and the capacitor C₃And a capacitor C₄The connection points b are connected and grounded; the resistor R₅Is connected with the single-pole double-throw analog switch U₂Pin a and the resistor R₃Between one end, the resistor R₃The other end of the output end of the transmitting circuit is connected with the input end of the transmitting output circuit; the resistor R₄Is connected with the single-pole double-throw analog switch U₂Between the pin S and the ground point; the capacitor C₅Is connected to the resistor R₃And a resistance R₄And a ground point.

2. The PWM isolation control output 4-20mA circuit according to claim 1, wherein the transmission output circuit comprises: current loop transmitter chip U₃And a triode Q₁；

Current loop transmitter chip U₃Pin VREG and the single-pole double-throw analog switch U₂The pins VCC are connected; the pin VREF is connected with the connection point a; pin IIN and the resistor R₃The other end is connected; pin IRET is connected to ground; pin V + and said triode Q₁The collector electrodes are connected; pin B and said triode Q₁The base electrodes are connected; pin E and said triode Q₁The emitting electrodes are connected; pin IO is a current output pin.

3. The PWM isolated control output 4-20mA circuit according to claim 2, further comprising: capacitor C₆And a capacitor C₇；

The capacitor C₆And a capacitor C₇In parallel, the capacitor C₆And a capacitor C₇A is connected withThe contact point is connected with the current loop transmitter chip U₃Pin VREG of (a) is connected and the other connection point is grounded.

4. The PWM isolation control output 4-20mA circuit according to claim 3, further comprising: bidirectional TVS tube D₁And bidirectional TVS tube D₂；

The bidirectional TVS tube D₁Is connected to the triode Q₁Collector and the current loop transmitter chip U₃Between pins IO; the bidirectional TVS tube D₂Connected to the current loop transmitter chip U₃Between pin IO and ground.

5. The PWM isolation control output 4-20mA circuit of claim 4, further comprising: capacitor C₁And a capacitor C₂；

The capacitor C₁And the bidirectional TVS tube D₁In parallel, the capacitor C₂And the bidirectional TVS tube D₂And (4) connecting in parallel.

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