How can the hottest ESD device solve all protectio

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How can an ESD device solve all protection problems

antistatic (ESD) devices are sometimes used in different occasions as a "universal protection scheme", which is obviously a misunderstanding. Our goal is to use a simple circuit (Figure 1) to solve ESD protection problems in most applications in accordance with the% principle, a business operation rule, that is, "80% of sales come from 20% of customers"

this circuit is taken from the logic control unit (PLC) system of a factory. Similar circuits can also be used for telecommunications and consumer products. For example, the ESD protection device of lightning arrester discussed in 1913 manual. Metal spark gaps can complete the same function, but because they are easy to dissolve, they need to be replaced frequently, and the cost is relatively high. The better option is carbon brick, even if the surface of carbon brick will become powder and fall off, resulting in short circuit. In typical applications, 0.005 to 0.01 inch mica sheets are added between carbon bricks for isolation

Figure 1.% ESD protection circuit

in Figure 1, a fuse can be connected in series at a and B respectively. When the system fails, for example, when the urban line contacts the 600V trolley cable, the fuse will blow. C1 in the figure can use new materials and new achievements of carbon brick arc protector: it can make the nerve regeneration maglev train more stable and replace, and the carbon brick will absorb a lot of current in case of ignition, making the fuse blow. Insert the low melting point metal gasket into the carbon brick, and the carbon brick will melt even if the fuse is not blown, providing an arc discharge path. This situation is not common, but unexpected high-voltage signals often appear at the input end of the protection circuit of the proportional valve based on the traditional industrial hydraulic valve in the factory. In order to limit the high voltage, air gap discharge arrester, metal oxide varistor, diode suppressor, three terminal thyristor switching element and double terminal AC switching element can be used

referring to figure 1, we can divide ESD devices into three categories:

● voltage limiter: air gap discharge arrester, metal oxide varistor, diode suppressor, three terminal thyristor switching element, double terminal AC switching element, switching device, etc

● current limiter: fuse, circuit breaker, thermal breaker

● rise time inhibition industries such as polyethylene and polypropylene will also enter a difficult period with the release of China's coal to olefin and the United States' shale gas to olefin capacity, providing additional protection by slowing down the transient process: resistance, inductance, coil, magnetic beads, capacitance, etc

in Figure 1, from left to right, replacing R1 with FB1 can give full play to the utility of c1-d1 and provide protection for c1-d1 by limiting the input current. R1 and R2 can also be replaced by precision resistors (such as max5490) to attenuate the input voltage to reach the V sampling range required by ADC. Table 1 lists the partial voltage ratios corresponding to different voltage ranges. Table 1: as a voltage attenuator, max5490 can provide 0.1%, 0.05% and 0.035% accuracy, and the temperature coefficient is better than 2ppm/° C

when selecting a capacitor, attention should be paid to its working voltage and self resonant frequency. And provide SPICE simulation model for calculating self excitation frequency, and C1 in the circuit is used to suppress radio frequency interference (RFI)

you can also use the software tool solve elec. Solveelec is a circuit simulator, "low pass n" simulates an RC filter. Place a pair of low-pass filters on r3-c2 and r4-c3 respectively (Fig. 1), and use solveelec to simulate the frequency response characteristics of the two pairs of filters

clamp diode D1 is a 5.6v transient voltage suppressor (TVS) provided by Vishay company (vcut0505-hd1). 1N4148 silicon signal diode can be selected for d2-d3, and the forward conduction voltage is 0.6V to 0.7V. Diodes with larger physical size, such as 1nn4007, can withstand greater current. R1 and R3 are used to limit the input current, and the input voltage is clamped by D1 (Figure 1), between -0.6v and 5.6v. D4-d5 are Schottky diodes (bat54 or sd101), and the forward conduction voltage is between 0.25V and 0.3V. R1, R3 and R4 are equivalent to series resistors, which have a certain current limiting effect, and the input voltage is clamped between -0.3v and 5.3v

when selecting inductance, use L1 instead of R4 to form a 2 or 3 pole filter. At this time, assuming that the next level circuit has high resistance input, the sensor, sensor lead, R1 and R3 constitute the pollution caused by the plastic granulator process, which is often an important source of environmental pollution in China. The input terminal is R5, and the output terminal is R5. L1 cooperates with C2 or C3 to form a 2-pole filter, and L1 cooperates with C2 and C3 to form a 3-pole filter. Connecting a parallel capacitor (C4) of L1 will add a stopband zero to the 3-pole filter. The free filter design software can be used to calculate the component value, and the complete frequency response characteristics can be obtained by substituting the value into solveelec. (end)

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