Protection circuit for three-wire system current output transmitter

A technology for protecting circuits and transmitters, applied in the direction of emergency protection circuit devices, emergency protection circuit devices, circuit devices, etc. for limiting overcurrent/overvoltage, and can solve the problem of overcurrent damage to diode D2, diode D2 or load resistance Damage, poor current limiting effect and other problems, to achieve the effect of reasonable and practical circuit and reduce the area of ​​circuit board

CN101667728AActive Publication Date: 2010-03-10KELI SENSING TECH NINGBO CO LTD
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Patent Information

Authority / Receiving Office
CN · China
Current Assignee / Owner
Publication Date
2010-03-10

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Abstract

The invention provides a protection circuit for a three-wire system current output transmitter. The protection circuit comprises clamping diodes D1 and D2 and a diode D4, wherein the clamping diodes D1 and D2 are connected between a power end of a transmitter and a current output end and between the current output end and the ground GND in turn; and the diode D4 is connected between the power endand a transmitter terminal of a VCC end and used for preventing reverse connection of a power supply. The protection circuit is characterized by additionally comprising a P channel reinforced type small signal MOS pipe Q1, wherein a source electrode S of the pipe Q1 is connected to a current output end of a transmitter output stage, a grid electrode G of the pipe Q1 is connected to the ground GND,a drain electrode D serving as the transmitter terminal for the current output is connected with a diode D3 with an isolation function in series. The structure of the circuit is more reasonable and practical and can full protect the power supply and output lines.
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Description

technical field

[0001] The invention relates to a port protection circuit of a three-wire current transmitter. Background technique

[0002] The current output type transmitter is widely used in industrial control sites, and its function is to amplify the signal (usually a voltage signal) of some sensors and convert it into a standard 4-20MA current signal. The working principle of this type of transmitter is generally to amplify the voltage signal first, and then convert the voltage to the current at the output stage. The output stage is generally composed of transistors or field effect transistors, and the actual application circuit diagram is shown in figure 1 .

[0003] The protection mechanism of the circuit is as follows:

[0004] Diodes D1 and D2 are clamping diodes to ensure that the level of the current output terminal is between GND-0.7V~VCC+0.7V. The function of diode D4 is to prevent reverse connection of the power supply, and R1 is a current-limiting resistor...

Examples

Embodiment Construction

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] In view of the above deficiencies, the present invention can provide all-round protection for the power supply and output lines of the transmitter. The schematic diagram is shown in figure 2 .

[0023] In the technical solution of the present invention, a three-wire current output transmitter protection circuit includes clamping diodes D1 and D2, a diode D4 is connected between the power supply terminal and the transmitter terminal of the VCC terminal to prevent reverse connection of the power supply. The key point of the invention is to remove the current limiting resistor and replace it with a P-channel enhanced small-signal MOS tube Q1 , Connect the source S of the tube Q1 to the output terminal of the transmitter output stage, the gate G is grounded, and the drain D is connected in series with the transmitter terminal with an isol...