Avalanche diode

An avalanche diode is a diode (usually made from silicon, but can be made from another semiconductor) that is designed to go through avalanche breakdown at a specified reverse bias voltage and conduct as a type of voltage reference.

The Zener diode exhibits an apparently similar effect in addition to Zener breakdown. Both effects are actually present in any such diode, but one usually dominates the other. Avalanche diodes are optimized for avalanche effect so they exhibit small but significant voltage drop under breakdown conditions, unlike zener diodes, that keep voltage always higher than breakdown. This feature provides better surge protection than simple zener diode and acts more like Gas discharge tube replacement.

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 or Transient voltage suppression diode because they "clamp" the maximum voltage to a predetermined 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.

Microwave frequency generation

If placed into resonant circuit, avalanche diodes can act as negative resistance device. IMPATT diode is avalanche diode optimized for frequency generation.

See also

• Transient voltage suppression diode