Transient state voltage restrains diode (TVS) calls grip again diode, it is at present circuit of a kind of when use generally tall efficiency on international protects parts of an apparatus, its exterior and common diode are identical, but can draw the surge power that is as high as thousands of tile however.

 

The main characteristic that transient state voltage restrains diode is to be below retrorse application condition, should bear when the big pulse of a high-energy quantity, its job impedance falls instantly to extremely low guide a value, allow big electric current to pass thereby, be in voltage clamp down on at the same time book a level, its answer time to be 10-12 millisecond only, because this can protect the nicety in electronic circuitry effectively yuan parts of an apparatus.

 

Transient state voltage restrains what diode allows to be in to surge electric current TA ＝ 250C, below condition of T ＝ 10ms, can amount to 50 ～ 200A. Two-way TVS can be in two direction absorb positive and negative power of instantaneous big pulse, go to voltage clamp down on book a level, two-way TVS applies to alternating current road, one-way TVS is used at dc road commonly. Can use at preventing be struck by lightning, prevent overvoltage, interference rejection, absorb surge power to wait, it is a kind of ideal protection parts of an apparatus. Be able to bear or endure suffer ability to use watt (W) expresses.

 

Transient state voltage restrains the main report parameter of diode

 

(1) puncture voltage V(BR)

 

Parts of an apparatus is inside the section that produces puncture, below I(BR) of experiment electric current, measure so that the voltage of two end calls parts of an apparatus puncture voltage, inside this area, diode makes the access of low impedance.

 

(2) IPP of electric current of peak value of the biggest retrorse pulse

 

When retrorse job, below pulse condition of the regulation, parts of an apparatus allows the electricity of peak value of the biggest pulse that carry. IPP and most tongs the product of voltage VC(MAX) , it is the maximum of power of transient state pulse.

 

When using, answer to choose TVS correctly, the power of surge of the biggest transient state that makes power PPR is more than pulse of rated transient state to may be appeared by protective parts of an apparatus or circuitry.

 

Transient state voltage restrains the classification of diode

 

Transient state voltage restrains diode to be able to press polarity cent to be mixed for odd polarity bipolar two kinds, can divide by utility for all sorts of circuit applicable general-purpose parts of an apparatus and special circuit are applicable special model parts of an apparatus. Be like: Environmental protection of electric current of all sorts of alternating voltage protector, 4~200mA implement, data line protector, coaxial cable protector, phone protector. If press,enclose reach internal composition to be able to divide for: Axial down-lead diode, biserial inserts TVS array continuously (applicable multi-line is protected) , stick a type, package type and high-power module type to wait.

 

Transient state voltage checks the application of diode

 

Apply extensively already at all of computer science department, communication equipment at present, hand in / appearance of ballast of direct current source, car, electron, electric home appliances<gj, instrument (kilowatt-hour meter) , of camera of RS232/422/423/485, I/O, LAN, ISDN, ADSL, USB, MP3, PDAS, GPS, CDMA, GSM, number.

 

Transient state voltage restrains the characteristic of diode

 

(1) add TVS diode on signal and power supply cord, can prevent microprocessor or odd the fat because of the instant develops an aircraft, the malfunction that the noise place of the surge that is like electrostatic discharge effect, alternating current source and switch power source brings about.

 

(2) electrostatic discharge effect can release the pulse that exceeds above of 10000V, 60A, can last 10ms; And general TTL parts of an apparatus, when encountering the 10V pulse that exceeds 30ms, can guide to attaint. Use TVS diode, can absorb the pulse that can cause parts of an apparatus to damage effectively, can eliminate disturb by what switch place causes between bus line (Crosstalk) .

 

(3) place TVS diode between line and ground connection, can avoid data and control bus line to be affected by unwanted noise.

 

Transient state report depresses those who make diode to choose skill

 

(1) be protected certainly the biggest dc of circuit or successive job voltage, specified level voltage of circuit and tolerance of ” of “ high end.

 

(2) TVS is rated and retrorse close to VWM should is more than or be equal to by the voltage of the biggest job of protective circuit. Be like chosen VWM too low, parts of an apparatus may enter avalanche or the regular job that because retrorse leakage current is too big,affect circuit. Serial join divides voltage, collateral join divides electric current.

 

(3) of TVS most tongs voltage VC should is less than by the attaint voltage of protective circuit.

 

(4) inside the pulse duration in the regulation, the PM of power comsumption of pulse of the greatest peak value of TVS must be more than the power of peak value pulse that is appeared by the likelihood inside protective circuit. In decided most tongs after voltage, electric current of pulse of its peak value should be more than electric current of transient state surge.

 

(5) the protection to data interface circuit, still must notice to choose the TVS parts of an apparatus that has C of right electric capacity.

 

(6) the polarity that chooses TVS according to utility and enclose a structure. Alternating current road is chosen bipolar TVS is relatively reasonable; Multi-line protection chooses TVS array more advantageous.

 

(7) temperature consideration. Transient state voltage is restrained implement can be in – 55 ℃ ～ + work between 150 ℃ . If need the temperature work that TVS changes in, because its are retrorse,leakage current ID is to follow increase and increase; Power comsumption writtens guarantee along with TVS lukewarm increase and drop, from + 25 ℃ ～ + 175 ℃ , about linear drops the addition that VBR of voltage of puncture of 50 ％ rain follows temperature increases by certain coefficient. Accordingly, must consult related goods data, consider the impact with temperature characteristic to its change.

 

Handling the best way that instantaneous pulse damages to component is instantaneous electric current from inductive component draw away. TVS diode is on circuit board with by protective route paralell connection, exceed circuit when instantaneous voltage after regular job voltage, TVS diode produces an avalanche, provide instantaneous electricity one exceeds low resistance access, its are instantaneous electric current passes through diode as a result by draw away, escape is protected component, and return to normal in voltage make be maintained all the time by protective loop before the value cut-off voltage. After ending when instantaneous pulse, TVS diode answers condition of Fu tall block automatically, whole return enters normal voltage. A lot of component are in after bearing for many times to pound, its parameter and function can arise degrade, and want the job to be inside limit range only, diode will not produce damage or degrade.

 

From above the process can see, when choosing TVS diode, must note the alternative of the following parameter:

 

1, VBR of voltage of the smallest puncture and I R of puncture electric current. VBR is the puncture tension with the least TVS, when 25 ℃ , under this voltage TVS be to won’t produce an avalanche. The 1mA electric current that has shed a regulation when TVS (when IR) , add at the voltage with polar TVS to be its V BR of voltage of the smallest puncture. Follow the disperse rate of the value by the VBR of TVS and mark, can mix VBR cent for 5 ％ 10 ％ two kinds. To the VBR of 5 ％ , v WM =0.85VBR; To the VBR of 10 ％ , v WM =0.81VBR. To satisfy IEC61000-4-2 international standard, TVS diode must be achieved can handle the smallest 8kV(to contact) with 15kV(air) ESD concussion, halfway semiconductor manufacturer was used on his product taller fight concussion standard. To certain have special demand can carry equipment application, the architect can choose component according to need.

 

2, ID mixes the biggest retrorse leakage current rated and retrorse cut off voltage VWM. VWM is diode is when whack but susceptive voltage, this voltage should is more than or be equal to by the regular job voltage of protective circuit, otherwise diode can end ceaselessly loop voltage; But it needs again as far as possible with be close to by the regular job voltage of protective loop, such ability won’t make in TVS job opposite of whole return face presses menace before. When this rated and retrorse those who cut off voltage VWM to be added at TVS is polar when it is in cut off condition reversely, the electric current that has shed it should is less than or be equal to its the biggest retrorse leakage current ID.

 

3, most tongs voltage VC and I PP of electric current of pulse of the greatest peak value. When the IPP of electric current of pulse peak value that is 20ms when duration has shed TVS, the voltage of the greatest peak value that in its two end appear is VC. V C, IPP mirrorred TVS dash forward wave control capacity. Of VC and VBR than calling grip factor, it is commonly between 1.2~1.4. VC is the voltage that diode offers in off-state, pass the voltage of TVS when ESD pounds condition namely, it cannot is more than be protected of loop can bear limiting voltage, otherwise component side faces the risk that is injured.

 

4, power of Pppm rated pulse, this is to be based on the biggest cut-off voltage and electric current of right now peak value pulse. To holding facility, generally speaking the TVS of 500W is enough. PM of power comsumption of pulse of the greatest peak value is TVS can power comsumption of pulse of the greatest peak value is worth susceptive. Be in specific most tongs below voltage, power comsumption PM is bigger, its dash forward of wave electric current bear ability is greater. Below specific power comsumption PM, clamp voltage VC is lower, its dash forward of wave electric current bear ability is greater. Additional, power comsumption of peak value pulse returns as undee as pulse, duration and environmental temperature to concern. And, TVS can pulse of susceptive transient state is nevermore, the pulse that component sets weighs Fu frequency (of duration and intermittent time than) for 0.01 ％ . If pulse of heavy Fu sex appears inside circuit, of power of pulse of Lv of take an examination accumulate, possible attaint TVS.

 

5, capacitance caliber C. Capacitance caliber C is by TVS the avalanche is writtened guarantee of sectional decision, measure below specific 1MHz frequency. The electric current of the size of C and TVS bears ability becomes direct ratio, c too the general makes question mark attenuation. Accordingly, c is the important parameter that circuit of data mind extent chooses TVS. Capacitor to data / the return with question mark higher frequency, the capacitor of diode is bigger to the interference of circuit, form noise or strength of attenuation question mark, because this needs a basis,the character of loop decides what choose the capacitor limits of component. High frequency loop chooses capacitor to answer commonly as far as possible small (like TVS of LCTVS, low capacitor, capacitor is not more than 3pF) , and not tall to capacitor requirement loop capacitor chooses but prep above 40pF.

 

Transient state voltage restrains diode character curve:

 

Explain:

VBR: Break down instant of voltage @IT- TVS turns into the dot of low impedance

VRWM: Maintaining voltage – the position that here level TVS opens to do not guide

VC: Approximate of voltage of clamp down on of @Ipp – of voltage of clamp down on is equal to 1.3*VBR

VF: guide electrify presses @IF – to pressure fall

IR: Converse leakage current ＠ VRWM

IT: Break down the test electric current of voltage

IPP: Dash forward electric current of wave peak value

IF: guide electrify flows

 

Graph curve of character of diode of 1 one-way TVS

 

Graph curve of character of diode of 2 two-way TVS

 

Graph voltage of 3 transient state restrains diode circuit principle