PLC output circuit with overcurrent protection

Abstract

The invention discloses a PLC output circuit with overcurrent protection. The PLC output circuit is connected with an external load and a power unit and comprises a switch control circuit and an overcurrent protection circuit, wherein the switch control circuit and the overcurrent protection circuit are sequentially connected. The overcurrent protection circuit comprises an overcurrent detection circuit, a locking circuit, an and gate circuit, a switching tube and a detection resistor, wherein the switching tube and the detection resistor are connected between the external load and the power unit in series. The PLC output circuit has the advantages that the overcurrent protection circuit is arranged, the switching tube Q with lower power can be selected, and therefore the cost is lowered, and the switching speed can be increased; when a short circuit or overcurrent occurs and a voltage value detected by the overcurrent detection circuit is larger than a reference voltage, the locking circuit locks output, and therefore the switching tube Q is controlled to be disconnected, and the purpose of overcurrent protection can be achieved; the number of adopted components is small, the structure is simple and the cost is low.

Description

technical field [0001] The invention relates to the field of PLC digital quantity output, more specifically, relates to a low-cost PLC output circuit with overcurrent protection. Background technique [0002] PLC (Programmable logic Controller, programmable logic controller) is an electronic device specially designed for digital operations in industrial environments. It has high anti-interference ability and load capacity, and has been widely used. It uses programmable memory to store programs, execute logic operations, sequence control, timing, counting and arithmetic operations and other user-oriented instructions, and control various types of machinery or production processes through digital or analog input / output. However, in practical applications, it is possible to mistakenly connect the PLC digital output port with power limitation to a high-power load, or short-circuit due to load damage, which will cause the port to burn out due to overcurrent, which will cause trou...

AI Technical Summary

Problems solved by technology

[0005] However, the above two methods have the following defects: 1) The PLC output is not over-current protected inside the PLC, but a high-power FET is directly used, but the high-power FET needs a large derating, which is wasteful under normal use Larger, and the power of the external DC power supply is unpredictable, and it is impossible to protect all short-circuit or over-current conditions. At the same time, for the PLC open-drain output, the use of high-power devices will result in a large parasitic capacitance and slow switching speed ; 2) Using an integrated circuit to protect the PLC output from overcurrent, the cost is too high

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