How is avalanche diode helped prevent overvoltage?

 

Common overvoltage protection method is “ active clamp (Active Clamping)” . Below this kind of circumstance, avalanche diode uses as direct feedback. If close to bring about inductance load to approach peak value too, conduct by avalanche diode to IGBT grid, and IGBT puts through afresh.

 

 

The graph indicated fundamental on: When voltage rises, diode is broken by block (A) . In extinct area, one each is sparked by the electron the instant of the avalanche, voltage drops suddenly the puncture voltage n under 30V, avalanche diode immediately puncture (B) . Before be started afresh, can maintain avalanche electric current to be stabilized inside short time only sometimes, and voltage rises again (C) . Puncture defer (D) namely the time between two puncture incident, cannot forecast.

 

The proposal will have the avalanche diode that improves noise performance to be used at active clamp press protection too, because of them can:

 

˙ falls in the retrorse voltage that rises quickly, faster puncture

˙ is in small electric current (under steadier breakdown voltage is had when ~1mA) , accordingly:

˙ prolongs the life of other parts of an apparatus, for example IGBT or Mosfet, result:

˙ is transducer or the application such as electric machinery controller saves cost, because package is less,need changes.

 

How does the noise of avalanche diode produce?

 

What the noise of avalanche diode comes from an avalanche is ceaseless put through and disconnect, namely the ceaseless generation of voltage peak value reachs his abrupt puncture () seeing a picture. Spark avalanche puncture has two precondition:

 

1.Put in enough puncture voltage to be used in order to arise at the intensity of critical electric field of collision ionization.

 

2.Put in free electron, form leakage current consequently.

 

For example, leakage current of 1.6pA = 1.6 X 10-12A is equal to the electronic velocity of flow that passes barrier layer to be every second 107 electrons, this is meant on statistic every 100ns can spark only avalanche. However, because not be every electron,can spark avalanche, spark actually time will be longer. Accordingly, spark the probability of avalanche puncture and discharge leakage current become scale. In other words: Leakage current is bigger, spark the probability of avalanche puncture jumps over tall or puncture defer time is shorter (in the graph: D) .

 

Between electron of two concussion leakage current, the retrorse tension that diode handles can rise to n of voltage of prep above puncture significantly. When next concussion only the electron sparks when the avalanche, the voltage of diode just can drop suddenly puncture tension level.

 

If voltage source provides enough electricity, for example 1mA, avalanche puncture can maintain oneself to move through successive collision ionization, produce stable avalanche electricity thereby.

 

But, if source electric current is too small, for example 100μA, drop suddenly under the avalanche voltage of puncture voltage n, make diode discharge, will bring about avalanche puncture to stop again instantly. At this moment, need proper time to make diode and line capacitance charge, make low source electric current achieves needs voltage n, next next electron ability sparks new avalanche. The put through ceaselessly and breaks channel to cause avalanche diode breakdown typical noise of this kind of avalanche.

 

The difference of diode noise function is visible also in the graph: Two Z diode showed in the graph (neat accept diode) puncture voltage limits, the retrorse electric current in 100μA (the puncture voltage that measures below IR) is 30V. Among them a diode is based on standard technology, use extremely small leakage current, another uses ” of technology of “ low noise. The neat accept diode that has ” of technology of “ low noise has dovisher voltage character, excel can keep constant inside short time only another diode of avalanche electric current (C) .

 

Power world offers the Z diode that uses ” of technology of “ low noise, these new generation products include SMF, BZD27, BZG 03, BZG04, BZG05, PLZ and VTVS series, because increase leakage current moderately (IR~10nA) and increased to spark apparently the possibility of avalanche puncture, reduced noise thereby, offerred for the user in small electric current (under the steadier breakdown when ~1mA) voltage and rise quickly the faster puncture of retrorse voltage.

 

Of diode noise further influencing factor

 

Leakage current increases along with temperature and show an index to rise, noise lifts along with temperature and reduce namely; Light still can release diode the free electron in extinct area, reduce noise level thereby. This means: The environment is jumped over all around dark colder, noise level is higher.

 

Author: Ruzhuoli Jürgen Gerber of manager of department of schism semiconductor product, TVS of branch of power world diode and ESD protection diode and EMI filter application and product project are advanced manager Jochen Krieger