Passive current detecting circuit

Abstract

The invention provides a passive current detecting circuit which is used for an output channel circuit and has the detection limit as low as 1 mA and the current tolerance as high as 400 mA. According to the passive current detecting circuit, one end of a solid-state relay receives control signals, the other end of the solid-state relay is connected with the emitting electrode of a first PNP transistor and the emitting electrode of a second PNP transistor, the base electrode of the first PNP transistor, the base electrode of the second PNP transistor and the collector electrode of the second PNP transistor are connected to be used as the output end of the circuit, the collector electrode of the first PNP transistor is connected with the first input end of an optical coupler through a resistor, the second input end of the optical coupler is connected with a circuit voltage, the first output end of the optical coupler outputs a current detecting signal, and the second output end and the third output end of the optical coupler are grounded.

Description

technical field [0001] The invention relates to the field of electronic circuits, in particular to an output current detection circuit applied in industrial control systems and safety signal systems. Background technique [0002] Industrial control systems and safety signal systems such as: avionics, railway signals, nuclear power and other industries, the controller realizes the opening and closing of the external controlled signal through the switch output channel. In order to determine the real output status of the port and the magnitude of the leakage current, a current detection circuit is generally designed at the output port. In order to ensure that the detection circuit does not affect the safety of the output, it is generally required that the detection circuit adopts a passive design. [0003] Such as figure 1 As shown, it is a common output channel circuit design, which is composed of a controller 1, an optocoupler 3, a current limiting resistor 6.1, and a curre...

AI Technical Summary

Problems solved by technology

This circuit can achieve a small current detection limit, but when the channel current is large, the power and voltage drop of the sampling resistor are large, which seriously affects the output function

Even if a zener tube is connected in parallel at both ends of the current sampling resistor for voltage clamping, the large power consumption on the current sampling resistor cannot be avoided, and it is not suitable for use in high current situations.

Another common design is to use electromagnetic conversion devices for current sensing, but the cost is high and bulky, and it is not suitable for multi-channel, PCB-mounted use cases

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