Isolated digital input circuit

Abstract

The invention relates to an isolated digital input circuit. The isolated digital input circuit comprises an input voltage threshold setting circuit, an optocoupler driving circuit and an optocoupler isolation circuit, wherein the input voltage threshold setting circuit is used for generating first voltage inputted into the optocoupler driving circuit according to input voltage; the optocoupler driving circuit is used for controlling on-off of the optocoupler isolation circuit according to a comparison result of the first voltage and built-in reference voltage of a voltage comparator; and the optocoupler isolation circuit is used for electrical isolation and signal transmission between different voltages and generating output voltage. The isolated digital input circuit sets an action threshold of input voltage and controls on-off of an optocoupler through the voltage comparator, the time of staying at an amplification state of the optocoupler is enabled to shortened near the action threshold of the input voltage, the switching speed is higher, accurate setting for the action threshold of the input voltage is realized, and the action threshold of the input voltage is avoided from being influenced by characteristics of the optocoupler.

Description

technical field [0001] The present disclosure relates to an input circuit, in particular to an isolated digital input circuit. Background technique [0002] Digital input circuit is an input circuit commonly used in industrial controllers, and it is mostly used for electrical isolation and signal transmission between different voltages. [0003] figure 1 For the digital input circuit in the related art, refer to figure 1 , The digital input circuit is composed of resistors R10, R9, filter capacitor C2, optocoupler U4 and output pull-up resistor R11. The optocoupler is an analog device. In the process from turning off to turning on, the output of the optocoupler enters the amplified state from the cut-off state; as the input voltage VIN increases, the output voltage VO gradually decreases to a fixed value. At this time, the optocoupler The output goes into saturation. In practical applications, when the input voltage VIN is near the operating threshold, the optocoupler U1...

AI Technical Summary

Problems solved by technology

[0004] However, due to manufacturing reasons, it is difficult to ensure that the amplification factor B of the optocoupler is exactly the same, and the voltage VF across the light-emitting diode in the optocoupler will change with temperature and current, so it is difficult to accurately determine the action of the input voltage VIN Threshold, when the input voltage VIN is near the action threshold, the optocoupler enters the linear amplification range, the voltage of the light-emitting diode in the optocoupler changes with the input voltage, the output voltage VO changes linearly, the output logic state is uncertain, and the switching speed is slow

Images