A kind of overcurrent and overvoltage protection circuit for 4-20ma current input circuit

Abstract

The invention discloses an over-current over-voltage protection circuit for a 4-20mA current input circuit. The over-current over-voltage protection circuit comprises a filtering rectification module, a switch control module, a voltage collecting module and a signal monitoring module, wherein the filtering rectification module filters out transient over-voltage impulse interference signals in input signals and avoids reverse connection of the input signals; the switch control module receives current signals output by the filtering rectification module and controls switching of a current loop; the voltage collecting module converts the current signals from the switch control module into corresponding voltage signals; the signal monitoring module monitors the voltage signals collected by the voltage collecting module and compares the voltage signals with a preset voltage threshold, the switch control module is instantly controlled to disconnect the current circuit if the voltage signals exceed the preset voltage threshold, and the preset voltage threshold can be set according to needs. According to the input over-current over-voltage protection circuit, over-current over-voltage protection functions can be achieved, safety and reliability are achieved, and influences on the input signals are extremely low.

Description

technical field [0001] The invention relates to a protection circuit, in particular to an overcurrent and overvoltage protection circuit for a 4-20mA current input circuit. Background technique [0002] In industrial applications, in order to overcome the influence of interference on the signal, 4-20mA current is usually used to transmit the signal. However, in the actual application process, it is inevitable that the 12V or 24V voltage signal of the system will be connected to the input signal terminal due to misoperation, or a large current will be output due to a signal source failure, or the signal line will be struck by lightning and high voltage will be coupled to the input signal terminal. The signal input equipment will be burned, the signal acquisition equipment will fail, and in serious cases, the entire system will be paralyzed, resulting in direct or indirect economic losses. [0003] In order to avoid overcurrent and overvoltage, some have added an independent ...

AI Technical Summary

Problems solved by technology

Some such as figure 2 The shown uses LM317L to realize over-current and over-voltage protection: the current flows from VI to LM317L, and flows out from the Output pin to R1. Since the voltage on the internal Adjustment pin is limited to 1.25V, the output current of LM317L is limited to Ilimit =1.25 / R1, so that the current is limited within 1.25 / R1

[0004] However, these protection circuits have limited functions for overvoltage and overcurrent protection, and have a greater impact on the input impedance of the circuit, which is likely to cause adverse effects on the acquisition accuracy of the input signal and the increase in the input impedance.

for example figure 1 Among them, the front-end resistor divider sampling and the subsequent switch circuit are in a cascaded relationship independent of each other, and only the latter circuit is turned off, and the circuit is not disconnected at the input end of the overvoltage signal. If there is a very high voltage for a long time After the connection, the protection circuit works, because the connection of the external voltage is not disconnected, a large current passes through Q1, it is likely to burn out Q1, and eventually lose the protection function

And as figure 2 In the circuit shown, this solution only relies on the LM317L’s own 1.25V voltage limit to realize the current limiting function. When the input input terminal is connected to an excessively high voltage, which exceeds the tolerance range of the chip LM317, the LM317L itself will be damaged, and eventually It will also lose the protection function. At the same time, due to the influence of the internal circuit of LM317L, the impedance of the input circuit is nonlinear, and the impedance of the input circuit will exceed 300 ohms at most.

Images