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What is an Avalanche Diode?

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  • Written By: G.W. Poulos
  • Edited By: Daniel Lindley
  • Last Modified Date: 26 November 2016
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    Conjecture Corporation
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Diodes are devices that block an electrical signal from passing through them in one direction, but allow a signal to pass in the other. When a standard semiconductor diode is blocking a signal, it is possible for the voltage of that signal to become too high for the diode to control. At that point, the diode will fail and allow the signal to pass, and will probably be destroyed as the voltage conducts though it. Dubbed the avalanche point of the diode, once this effect begins, it usually will not stop until it has run its course, devastating many, if not all, of the circuit components in its path. An avalanche diode is a special type of diode that can withstand the avalanche event and use the avalanche effect in its normal function.

All semiconductor diodes are constructed of two pieces of semiconductor material, usually silicon, fused together. One piece of the material, the cathode, will have a positive charge. The second piece, the anode, will have a negative charge.

These diodes control the direction of circuit flow in circuits. When an electrical current is applied to the diode’s anode, it traverses the positively charged material toward the negative cathode and then passes out of the cathode to the rest of the circuit. A diode operating in this state is forward biased.

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If the same current is connected to the cathode, it will simply come to rest with the identical charge of the cathode and be blocked by the diode. A diode in this state is reverse biased. Should that voltage be sufficiently high, however, it can have enough power to jump through the cathode and reach the positive anode. If this occurs, the current will be conducted out of the diode’s anode, and the diode will be in an avalanche condition. This condition will typically destroy a standard diode, as well as any other circuit components that lie between the diode and a grounding point.

An avalanche diode is designed in a very specific way so it can use the avalanche effect. Instead of waiting for voltage to become too large for the diode to handle and avalanche out of control, an avalanche diode intentionally starts the avalanche effect at a predetermined voltage. This predetermined voltage is not strong enough to damage the diode, which allows the avalanche diode to conduct the excessive power away from the circuit to a ground. In this manner, an avalanche diode works much in the same way that a spillway allows a dam to redirect excessive floodwaters.

The avalanche diode sees frequent use in circuits to provide protection against unwanted or unexpected voltages that might otherwise damage circuits. Such diodes usually have their cathodes connected to the circuit’s main path of electrical current and the anodes to an electrical ground. This configuration allows them to redirect threatening voltages directly to ground, as opposed to allowing them to travel through the circuit and destroying it. Avalanche diodes in this configuration act as clamping diodes since they fix, or clamp, the maximum voltage a circuit will experience to a preset level.

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