Yuansheng Da take you to understand what TVS is, and how to select?

In the design of the circuit, the safety performance of the product is one of the indispensable links, as one of the protective devicesTVSHow much do you know about it?Transient Voltage SuppressionTransient voltage suppression diode, for shortTVS.

Its protection principle is similar to the voltage regulator diode, is the use of reverse breakdown to stabilize voltage, butTVSThe response speed of the tube is much faster than that of the regulator. whenTVSWhen the tube is affected by the reverse transient high energy impact, it can change the impedance between the two stages into low impedance at a very high speed (subnanosecond level), so it has a good surge power absorption capacity, the voltage between the two stages clamp at a predetermined value, and effectively protect the back-end components of the circuit.

TVSOperating characteristic curve

Vrwm: refers to the maximum reverse operating voltage, also refers to the turn-off voltage. At maximum reverse currentIRDown, the voltage measured, In generalVrwmis(0.8~0.9)*Vbr. The turn-off voltage must be greater than or equal to the normal operating voltage of the circuit, but not much greater than andVbrIt doesn't matter, too much bigger, could lead toTVSIt doesn't work.VrwmNeed to be greater than the circuit in normal operating time voltage, generally if a12VThe system, weTVStheVrwmCan choose (12V*1.3=15.6V).

Ir@Vrwm: Maximum reverse leakage current.

Vbr@It: means to pass the specified test currentItThe voltage of PI, this is thetaTVSSignal voltage of the tube opening, i.e. from this pointTVSEnter the avalanche breakdown.

Max Ipp: Maximum reverse peak pulse current.

Vc@Max Ipp: refers to specificIppWhen the current is current, the surge passes throughTVSClamp voltage. Maximum clamp voltageVcBe less than or greater than the maximum operating voltage in the circuit. In general if a12VThe maximum voltage of the system may be reached18VWeTVStheVbrCan choose (18V*1.5=27V).

Ppk(8*20us): refers toTVSThe maximum power passing instantaneously on the device is10/1000usand8/20usTwo different energy waveforms. Equal to the clamp voltageVcAnd peak pulse currentIppThe product of PI reflectsTVSThe surge suppression capability of the device, the rated maximum pulse power, must be greater than the maximum transient surge power occurring in the circuit.

C: refers to the parasitic capacitance whenTVSAt high speed signals such asETH(Ethernet),USB. General choice is less thanpfthe smaller the better If the low speed signal, generally can choose dozenspFRight and left.

10/1000usand8/20usTest the wave forms for two different surges, which have different energies.8/20usThe pulse refers to8usreach100%Ipp.20usreach50%Ipp.

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