CN112969260A

CN112969260A - Anti-interference driving circuit based on Schmitt trigger

Info

Publication number: CN112969260A
Application number: CN201911285390.0A
Authority: CN
Inventors: 于士振; 段士龙; 华雯怡
Original assignee: Shanghai Aviation Electric Co Ltd
Current assignee: Shanghai Aviation Electric Co Ltd
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2021-06-15

Abstract

The invention discloses an anti-interference driving circuit based on a Schmitt trigger, which comprises a diode isolation unit, an anti-thunder peak surge unit, a first-order low-pass filtering unit, a Schmitt trigger, a switch driving unit and an LED which are sequentially connected, wherein the Schmitt trigger is provided with an upper limit threshold and a lower limit threshold, when an output signal of the first-order low-pass filtering unit is greater than the upper limit threshold, the Schmitt trigger outputs a turn-on signal to the switch driving unit to light the LED, and when the output signal of the first-order low-pass filtering unit is less than the lower limit threshold, the Schmitt trigger outputs a turn-off signal to the switch driving unit to light the LED. The invention has the advantages that: the lightning protection device has the functions of resisting lightning, spikes, surges and noise interference of onboard signals.

Description

Anti-interference driving circuit based on Schmitt trigger

Technical Field

The invention relates to a signal interface anti-interference driving circuit, in particular to an anti-interference driving circuit based on a Schmidt trigger.

Background

The airborne warning system carries out light warning in a mode that the signal board is lightened by the LED signal lamp. In many cases, the input signal of the warning light box comes directly from the aircraft sensor, and the sensor signal presents diversity if the sensor signal is of a switch type, and relates to a switch circuit controlled by a relay, a switch circuit controlled by an analog circuit, or other types of switch circuits and the like. The purely mechanical switch circuit has almost no influence on the product performance, and the analog circuit controls the switch circuit to generate an interference signal if leakage current exists under the condition of an off state (no signal), so that the signal off state is not true in the absence of the signal.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a novel anti-interference driving circuit based on a Schmitt trigger.

In order to achieve the purpose, the technical scheme of the invention is as follows: an anti-interference driving circuit based on a Schmitt trigger comprises a diode isolation unit, an anti-lightning peak surge unit, a first-order low-pass filtering unit, a Schmitt trigger, a switch driving unit and an LED which are sequentially connected, wherein the Schmitt trigger is provided with an upper limit threshold value and a lower limit threshold value, when an output signal of the first-order low-pass filtering unit is greater than the upper limit threshold value, the Schmitt trigger outputs an opening signal to the switch driving unit to light the LED, and when the output signal of the first-order low-pass filtering unit is less than the lower limit threshold value, the Schmitt trigger outputs a closing signal to the switch driving unit to light the LED.

As a preferred scheme of the anti-interference driving circuit based on the Schmitt trigger, the Schmitt trigger is of the same phase type.

As a preferred scheme of the anti-interference driving circuit based on the Schmitt trigger, the Schmitt trigger is of an inversion type.

Compared with the prior art, the invention has the beneficial effects of at least having the functions of resisting lightning, peak, surge and on-board signal noise interference. And the circuit has strong anti-interference capability. The voltage threshold value required by the signal interface processing circuit can be obtained by configuring the resistance value of the divider resistor.

Drawings

Fig. 1 is a schematic diagram of an in-phase schmitt trigger-based circuit according to the present invention.

Fig. 2 is a schematic diagram of a circuit based on an inverted schmitt trigger according to the present invention.

Detailed Description

The invention will be described in further detail below with reference to specific embodiments and drawings. Here, the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Referring to fig. 1, a single power supply in-phase schmitt trigger positive control interference rejection interface driving circuit is shown. The circuit mainly comprises a lightning, peak and surge resistant circuit formed by connecting a diode in parallel, a TVS tube and a piezoresistor, a first-order low-pass filter circuit, an in-phase Schmitt trigger circuit formed by a comparator and a bleeder resistor, and a switch driving circuit.

The same-phase Schmitt trigger anti-interference interface driving circuit based on single power supply. When a 27V/high on signal is sent by the circuit receiver, the received voltage signal exceeds the threshold value of the in-phase Schmitt trigger, the in-phase Schmitt trigger outputs a positive control signal to drive the Q1 to be conducted, and therefore the LED signal lamp is driven to be lightened. D3 and RV1 are connected in parallel to form a lightning, spike and surge resistant circuit for protecting a voltage comparator chip. During model selection, the limiting voltage of the voltage dependent resistor is less than the maximum clamping voltage of the TVS tube. The TVS tube has a faster reaction speed than the piezoresistor, and when the circuit is subjected to thunder, peak and surge, the TVS tube clamps the voltage before the piezoresistor acts, and at the moment, because the limiting voltage of the piezoresistor is less than the maximum clamping voltage of the TVS tube, the piezoresistor acts, and most of the peak current flows through the piezoresistor. Therefore, the lightning, peak and surge resistant protective film plays a role in resisting lightning, peak and surge and protects components from being damaged. The resistors R1, R2 and C2 form a first-order passive low-pass filter, and the critical frequency of the first-order passive low-pass filter is as follows:

the interference frequency noise is divided by the rate. For an in-phase schmitt trigger, the threshold is shown in equation (1).

Neglecting the forward conduction voltage drop of the diode in the derivation process of the formula, R7 < R3+ R6)

As can be seen from equation 1: the required voltage threshold value can be obtained by changing the resistance value of the resistor, the circuit is simple to realize and has strong anti-interference capability, the oscillation phenomenon is prevented, and the stability of the circuit is improved. The D4 zener functions to prevent damage to the voltage comparator devices from ground undershoots.

Fig. 2 shows a single-power-supply reverse schmitt trigger negative control anti-interference interface driving circuit, which adopts a single-power-supply reverse schmitt trigger. Unlike the in-phase schmitt trigger, the first-order passive low-pass filters R1, C2 and TVS are connected to the outside of the isolation diode D1, which has the advantage that the isolation diode has an influence on the reliability of the circuit due to the node capacitance of the diode itself under the condition of high-frequency interference. The first-order low-pass filter is connected to the front end of the isolating diode D1, so that high-frequency interference can be effectively filtered, the anti-interference capability of the circuit is improved, and the TVS plays a role in lightning resistance and spike protection.

For an inverted schmitt trigger, the threshold is shown in equation (2).

Neglecting the forward conduction voltage drop of the diode in the derivation process of the formula, R7 < R6+ R4// R5)

It should be noted that the output of the anti-interference interface driving circuit based on the schmitt trigger needs to be isolated:

the schmitt trigger is an amplifier with positive feedback, the output of which is fed back to the positive input end of the voltage comparator through a feedback resistor R, so the output needs to be isolated. If the isolation is not carried out, the output voltage is influenced by the carried load, and the voltage output and fed back to the positive phase input end of the voltage comparator changes along with the different carried loads, so that the required threshold value of the Schmitt trigger changes, and the normal work of the circuit is influenced.

The foregoing merely represents embodiments of the present invention, which are described in some detail and detail, and therefore should not be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An anti-interference driving circuit based on a Schmitt trigger is characterized by comprising a diode isolation unit, an anti-lightning peak surge unit, a first-order low-pass filtering unit, a Schmitt trigger, a switch driving unit and an LED which are sequentially connected, wherein the Schmitt trigger is provided with an upper limit threshold and a lower limit threshold, when an output signal of the first-order low-pass filtering unit is greater than the upper limit threshold, the Schmitt trigger outputs a turn-on signal to the switch driving unit to light the LED, and when the output signal of the first-order low-pass filtering unit is less than the lower limit threshold, the Schmitt trigger outputs a turn-off signal to the switch driving unit to light the LED.

2. The schmitt-trigger-based anti-jamming driving circuit according to claim 1, wherein the schmitt trigger is of the same phase type.

3. The schmitt-trigger-based anti-jamming driving circuit according to claim 1, wherein the schmitt trigger is an inverting type.