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Should be fully taken into account and meet the requirements of anti-interference, there are three basic elements of interference:

(1) the interference source, interference components, refers to equipment or signal, using mathematical language to describe as follows: du/dt, di/dt.

Is the source of interference. Such as: lightning, relay, silicon controlled rectifier, motor, high frequency clock can become sources of interference.

(2) the propagation path, the interference from the source of interference to sensitive device access or media. The typical interference propagation path is through

Wire conduction and space radiation.

(3) sensitive device, which can easily be interference. Such as: A/D, D/A converter, microcontroller, digital IC, weak signal amplification

Device etc..

The basic principles of anti-jamming design is: to suppress the interference source, cutting jam propagation path, improve the anti-interference performance sensitive devices.

(similar to the prevention of infectious diseases)

1 interference source suppression

Interference source suppression is as far as possible to reduce the interference source of du/dt, di/dt. This is the most preferable anti-interference design and the most important

The principle, can often play a multiplier effect. Reduce the interference source of du/dt is mainly through the interference source both ends parallel capacitor

To achieve. Reduce the interference source of di/dt is the series inductance or resistance to interference source circuit and increase the freewheeling diode is implemented.

The following common measures to suppress the interference source:

(1) to increase the relay coil freewheeling diode, eliminate the generated EMF interference disconnect the coil. Just add a freewheeling diode will

The relay turn-off time lag, increase the zener diode relay can act more times in unit time.

(2) in the relay contacts at both ends and then spark suppression circuit (usually RC series circuit, the resistance generally choose several K to tens of K, electric

Volume 0.01uF), reduce the electric spark effect.

(3) to the motor and filter circuit, capacitance, inductance lead to attention as short as possible.

(4) on the circuit board and connected to each IC to a 0.01 μ F ～ 0.1 μ F high frequency capacitance, in order to reduce the influence of IC on power supply. Be caref

High frequency capacitance wiring, connection should be close to the power supply end and try to thick and short, otherwise, is equivalent to increasing the equivalent capacitance in series electrical

Resistance, will affect the filtering effect.

(5) to avoid the 90 degree line wiring, reduction of high frequency noise emission.

(6) the two ends of the thyristor and then RC suppression circuit, reduce the noise produced by the controllable silicon (serious noise may be the SCR

Breakdown).

According to the propagation path interference can be divided into two types of conducted interference and radiated interference.

The so-called conduction interference refers to the interference sensing device through a wire communication. High frequency noise and useful signal frequency band is different, can

By increasing the filter method in wire cut off the high frequency interference noise propagation, sometimes also can add isolation optocoupler to solve. Electric

Noise source of the greatest danger, special attention should be paid to treatment. The so-called radiated interference is the sensitive device stem through space to the radiation propagation

Perturbation. The solution is to increase the interference source and sensitive device in the distance, with the lines to isolate them and on the sensitive device drain

Cover.

2 commonly used measures of cutting jam propagation path is as follows:

(1) considering the power of mcu. The power supply is well done, the whole circuit anti-interference is solved by half. Many single

Machine is very sensitive to the noise of power, to single chip power supply filtering circuit or regulator, to reduce power supply noise on the single chip microcomputer

Interference. For example, can be composed of PI type filter circuit using magnetic beads and capacitance, of course requirements is not high also available 100.

Instead of magnetic resistance.

(2) if the MCU I/O port is used to control the motor noise device, between the I/O and the noise source should be added to increase isolation (PI

Shape filter circuit). Control of motor noise, between the I/O and the noise source should be isolated (increased PI filter

Circuit).

(3) note crystal wiring. Crystal and microcontroller pin as close as possible to the ground, with the clock compartment, the crystal oscillator shell grounding

And fixed. This measure can solve many difficult problems.

(4) reasonable zoning in circuit board, such as strong, weak signal, digital, analog signal. The interference source as far as possible (such as motor, relay

Device) and sensitive element (such as SCM) away from the.

(5) number of land lines to isolated areas and simulation, digital simulation and to be with the separation, finally at a point is connected to the power supply. A/D,

D/A chip wiring is also based on this principle, the manufacturer distribution A/D, D/A chip has considered this requirement pinout.

(6) the ground and high power devices to be earthed separately, in order to reduce the mutual interference. High power devices as much as possible on a circuit

Plate edge.

(7) power line in the microcontroller I/O port,, circuit board connecting line etc.Key place using anti-jamming elements such as beads, magnetic, electric

Source filter, shield, can significantly improve the anti-interference performance of the circuit.

3 to improve the anti-interference performance sensitive devices

To improve the anti-interference performance sensitive device is defined from the sensitive device here considered to minimize the pickup to interference noise, and never

Methods the normal state as soon as possible.

The following common measures to improve the anti-jamming performance of sensitive devices:

(1) when wiring circuit to minimize the size of ring, in order to reduce the induction noise.

(2) the wiring, power line and rough ground to as much as possible. In addition to reducing the pressure drop, the more important is to reduce the coupling noise.

(3) single-chip idle for I/O port, not suspended, to ground or power. Other IC idle end without changing the system

Logic of the ground or power.

(4) to use power monitor and watchdog circuit, such as: IMP809, IMP706, IM