Avalanche diode

An avalanche diode is a diode (usually made from silicon, but can be made from another semiconductor) that is designed to break down and conduct at a specified reverse bias voltage.

The Zener diode exhibits an apparently similar effect, but its operation is caused by a different mechanism, called Zener breakdown. Both effects are actually present in any such diode, but one usually dominates the other. Zener diodes are typically restricted to a few tens of volts maximum, but silicon avalanche diodes are available with breakdown voltages of over 4000 V.[1]

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Uses

Protection

A common application is protecting electronic circuits against damaging high voltages. The avalanche diode is connected to the circuit so that it is reverse-biased. In other words, its cathode is positive with respect to its anode. In this configuration, the diode is non-conducting and does not interfere with the circuit. If the voltage increases beyond the design limit, the diode suffers avalanche breakdown, causing the harmful voltage to be conducted to earth. When used in this fashion they are often referred to as clamper diodes because they "clamp" the voltage to a predetermined maximum level. Avalanche diodes are normally specified for this role by their clamping voltage V_BR and the maximum size of transient they can absorb, specified by either energy (in joules) or i²t. Avalanche breakdown is not destructive, as long as the diode is not allowed to overheat.

RF noise generation

Avalanche diodes generate radio frequency noise; they are commonly used as noise sources in radio equipment. For instance, they are often used as a source of RF for antenna analyzer bridges. Avalanche diodes can also be used as white noise generators.

See also

• Avalanche photodiode
• Avalanche breakdown
• Zener diode
• Transil
• Varistor
• Voltage stabiliser

References

• Richard C Jaeger (1997). Microelectronic Circuit Design, ISE, McGraw-Hill. ISBN 0-07-114386-6. 
• Carl David Todd (1970). Zener and avalanche diodes. Wiley-Interscience. ISBN 0-471-87605-4. 
• SKa 1/13 Avalanche diode datasheet, SEMIKRON.
• DSZ412SE Avalanche Diode Catalog listing, Dynex Semiconductor.