Avalanche diodes, also known as avalanche breakdown diodes or simply avalanche diodes, are semiconductor devices designed to operate in a special region of their voltage-current characteristic called the avalanche breakdown region. They are used primarily for their unique property of exhibiting the avalanche effect, which occurs when a small current through the diode leads to a much larger current due to the avalanche multiplication effect.
Here's how avalanche diodes work:
Avalanche breakdown: Under normal conditions, when the voltage across a diode is increased, the diode will eventually reach a point where it conducts current. In standard diodes, this region is known as the forward bias region, and the current increases rapidly with voltage. However, in avalanche diodes, once the voltage reaches a certain critical level (avalanche voltage or breakdown voltage), the diode undergoes avalanche breakdown. In this region, the diode experiences a rapid increase in current due to the generation of electron-hole pairs by the impact ionization process.
Avalanche multiplication: During avalanche breakdown, the electrons in the diode gain enough energy to collide with the atoms in the semiconductor crystal, creating additional electron-hole pairs. These new electron-hole pairs can also gain energy and create more pairs through additional collisions, leading to a chain reaction-like process known as avalanche multiplication. As a result, the diode's current increases significantly, allowing it to handle much higher currents than what it could support in the forward bias region.
The unique behavior of avalanche diodes makes them useful in various applications, especially in high-voltage scenarios:
Voltage clamping: One of the primary applications of avalanche diodes is voltage clamping. When used in a circuit, they limit the voltage across the load by conducting once the voltage exceeds the diode's avalanche breakdown voltage. This helps protect sensitive components from excessive voltages.
Surge protection: Avalanche diodes are employed in surge protection circuits to safeguard electronic devices from voltage spikes and transients. When a sudden voltage surge occurs, the avalanche diode enters the avalanche breakdown region, shunting the excess current away from the protected components.
Overvoltage protection: In high-voltage systems, avalanche diodes act as overvoltage protectors. If the voltage rises above a certain threshold, the diode triggers the avalanche breakdown and prevents further voltage increase, protecting the circuit.
High-voltage rectification: In certain specialized applications, avalanche diodes can be used for high-voltage rectification, converting alternating current (AC) to direct current (DC) in high-voltage circuits.
Due to their ability to handle large currents and provide effective voltage protection, avalanche diodes find use in various high-voltage applications across industries, including power distribution, telecommunications, automotive electronics, and industrial systems.