Semiconductor Diodes Notes: Breakdown Mechanism

Breakdown Mechanişm Avalanche breakdown:- When the reverse voltage is increased, the eterton electric field across the junchon increases and the es are accelerated. The high energetic elechong, by collision, break covalent bonds and more elecbang are again produced This causes é's again knock out es by collision. This chain reachon takes place and an avalanche of elechons are produced. This Cumulative phenomenon is called avalanche breakdom The junchon breaks down for a certain reverse Voltage. The magnihide of avalanche break down voltage increases with orise in temperalzore Lener Breakdown:- When external field is very unterge, the electric field directly Cauge covalent bonds to break and a large no: of elector-hole paves Cause are produced. This Sudden ouse in current and the junchon breakdown This happens when the width of depletion layer is small. for this too sregions of the pin junction must be heavily doped. This breakdown is called gener bacakdown, can be explained on the basis of gener effect. During zener breakdown the eş are not Created by Colliscon, but by breaking covalent bonds under the appred reverse bias. Lenes Breakdown Avalanche breakdown The process in which the es move across the barrier from the valence band of p-type material to the Conduction band of n-type material is known as Zener breakdown. This is observed in Zener diodes having a zener breakdown voltage, below The valence electons are Pulled unto conduchon clue to the high electric held is to the neverow depletion region The process of applying high voltage and increasing the free es or elechic current in semiconductors and insulating materials is called an avalanche break down This is observed in Zener diode having a zener breakdown voltage, greater than 67/8V- The valence elechons are pushed to conduchon due the energy imported by accelerated elechong, which gain their velody due to their colligen with other atomy The increase in temperature decreases the break down Voltage The increase in temperahure increases the breakdown vol bye. It occurs in dudes that It occurs in diodes that are highly doped. are lighty doped Dynamic veuseştance (11) ac resistance (Mac): Raho of a small change in voltage corresponding to change in current. Does not obey ohm's law. Resistance offered by the Junchon depends upon the applied voltage = at which the yanchon breakdown is called the break down voltage k 3. The reverse current down voltage is corresponding to the break called the breakdown current Ik 4. The reverse voltage V₂ corresponding to any point Pon the linear portion of the reverse charactersties curve is called the gener voltage V 5 The ratio ga small change in zener voltage (dv) to the covoresponding small change in the Zener current (dI₂) is called the gener dynamic resistance z 6. The Zener diode will not be broant just because it is on the breakdown region. 1. The voltage beyond which the reverse current increases rapidly is called twin over vollage. 8. Zener diode is used as voltage regulator whieras the ordinary diode is used for rectification Application: Lener diate as voltage Regulator. Vanad sput voltage I cercut current I Load current I→ zener current Voltage regulator is an electronic circuit that provides a stable De Voltage independent of the load current, temperature and AC line Voltage variations A zener diode of break doum voltage Vz iş Meverge connected to an input voltage Source Vi across a load resistance R and series resştance R. The Voltage across the gener will reas remain Steady at its break doum voltage fer all the Values of Zener current I as long as the current remains in the break down regeon. Hence να regulated De output voltage = ½ & obtained across R, whenever the input voltage remains within a minimum and maximum voltage Basically there are 2 type of regulations:- a) Line regulation: In this type of regulation, Series resistance and load resistance are fixed, only speed only input voltage is changing Output voltage remains the same as long as the input voltage is maintained above a minimum value b) Load Regulation : In this type of regulation, input voltage is fured and load rexstance is varying Output volt remaing same, as long as load resistance is maintained above a minimum value 4 Rectification Application of ordinary diode The process in which ac voltage is convert into Q de voltage is called rechfication The circuit used for this conversion is known as rectifier.