Slide 1

Special PurposeDiodesZener Diode

Already covered..Constant Current DiodesExactly opposite to Zener diode

Instead of voltage these diodes hold the current constant

Also called as current regulator diodes

IN5305 is a constant current diodeWith a typical current of 2 mA over a voltage range of 2 V to 100 VSome examples of devices using current limiting diodes are

waveform generator ckt. timing circuits and battery chargers. Current limiting diodes can also be used as a constant current source for driving LEDs

Step Recovery Diodes(SRD)

SymbolAlso called as snap diode

During positive half cycleSRD conducts like an ordinary diode

During negative half small reverse current exists for a whileDue to stored charges then suddenly it drops to zero AND IT APPEARS THAT THE DIODE IS SNAPPED OPENUsed in frequency multiplier circuitharmonic generation or harmonic multipliers and also for pulse shaping.Back DiodeSchematic symbol is same as Zener Diode

V-I CharactersticsZener diodes normally have breakdown voltages greater than 2 V

By increasing the doping level We make the Zener effect to occur at near ZeroForward conduction still occurs at 0.7 V

But reverse conduction starts at -0.1 V approx.

Conducts better in reverse direction than in forward for weak signals

Hence called Back DiodeUsed to rectify weak signals

Whose peak amplitude Are Between 0.1V to 0.7 VSchottky Diode

SymbolThe Schottky diode operates only with majority carriers.There are no minority carriers and thus no reverse leakage current as in othertypes of diodes.When forward-biased, the higher energy electrons in the n region are injectedinto the metal region where they give up their excess energy very rapidly.

Since there are no minority carriers, as in a conventional rectifier diode, thereis a very rapid response to a change in bias.

The Schottky is a fast-switching diode, and most of its applications make useof this property.

It can be used in high-frequency applications and in many digital circuits todecrease switching times.Photo diodes

SymbolAphotodiodeis a type ofphotodetectorcapable of convertinglightinto eithercurrentorvoltage, depending upon the mode of operation.

The common, traditionalsolar cellused to generate electricsolar poweris a large area photodiode.A photodiode is designed to operate inreverse bias.

Material

wavelengthrange (nm)Silicon1901100Germanium4001700Indium gallium arsenide8002600Lead(II) sulfide