An input protection circuit of a multi-range voltage acquisition device

Abstract

The invention discloses an input protection circuit of a multi-range voltage acquisition device. The input protection circuit comprises a rectifier, a constant current source module and a floating power supply. One alternating current end of the rectifier is connected with the signal input end, and the other alternating current end of the rectifier is connected with the signal output end. The current input end of the constant current source module is connected with the common cathode of the rectifier, and the power supply end of the constant current source module is connected with the common anode of the rectifier; The floating power supply is connected between the current output end of the constant current source module and the common anode of the rectifier, the negative electrode of thefloating power supply is connected with the current output end of the constant current source module, and the positive electrode of the floating power supply is connected with the common anode of therectifier. During normal operation, low impedance enables signals to pass through easily, the signal-to-noise ratio and the bandwidth are not reduced obviously, and a subsequent circuit is protected from being damaged in a high-resistance state during overvoltage. Positive overvoltage and negative overvoltage are rectified by a rectifier bridge, conduction and cut-off of a diode are automaticallyswitched, constant current source current is always kept at a constant value, and time delay caused by a detection and feedback mechanism does not exist.

Description

technical field [0001] Embodiments of the present invention relate to the technical field of protection circuits, in particular to an input protection circuit of a multi-range voltage acquisition device. Background technique [0002] The voltage acquisition device divides the input range of the device into multiple ranges in order to adapt to a wide input voltage range and require sufficient resolution. For example: the range of an AC voltmeter can be 1V, 10V, 100V, 1000V, assuming that the range of the meter head is 10V, then the device includes a range switching circuit, an attenuation circuit, and an amplification circuit. The 1V range is enlarged by 10 times, and the 10V range is enlarged. 1 times, 100V range attenuation 10 times, 1000V range attenuation 100 times. The prior art uses a multi-tap resistor divider, the switch selects different taps to obtain different attenuation multiples, and then the signal is sent to a variable gain amplifier, and the ratio of the res...

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Problems solved by technology

[0005] Option 2, when there is no overvoltage, the MOSFET is turned on, and the series resistance is very low, which has little effect on the bandwidth. However, there is a detection and feedback control circuit in this solution. When the overvoltage occurs, the circuit first appears overcurrent, and then it is detected and fed back to the gate of the MOSFET. There is a delay in the process, and the gate capacitance of the high-voltage MOSFET is large, the gate voltage is not reduced quickly enough, and the rapidly increasing overvoltage MOSFET cannot be turned off in time, which may cause protection failure. In addition, the scheme is complicated, and the number of components used is large. Two floating power supplies generate positive and negative voltages. The more components there are, the lower the reliability is. Usually, the circuits for generating floating power supply are complicated. The two floating power supplies require more components and occupy more PCB area. These floating circuits are connected to the signal ground on the PCB. If stray capacitance exists, the more components, the larger the area, the greater the stray capacitance. This stray capacitance is connected in parallel to the input circuit, which increases the input capacitance, which is not good for high-frequency and high-speed signal measurement.

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