ReverseBias

ReverseBias is a term used in electronics to describe the biasing condition of a PN junction or transistor junction when the applied voltage opposes the direction that would cause forward current. In this condition the depletion region widens, minority carriers are drawn away, and the device conducts only a small leakage current until a breakdown voltage is reached. It is contrasted with forward bias, under which current flows readily.

In diodes, reverse-biased operation largely blocks current, effectively behaving as an open circuit under normal voltages. The reverse current is small and increases with temperature. If the applied reverse voltage exceeds the device’s breakdown rating, the diode may conduct heavily in reverse. Some diodes, such as Zener diodes or avalanche diodes, are designed to enter controlled breakdown at a specified voltage, which is used for voltage regulation or protection.

Reverse bias also plays a key role in photodiodes and high-speed electronics. For photodiodes, reverse bias widens the depletion region, reducing capacitance and increasing speed and carrier separation, which improves sensitivity and response time. PIN diodes, featuring an intrinsic layer, are operated under reverse bias to achieve higher breakdown voltages and faster switching. In protection circuits, components designed to conduct in reverse, such as transient voltage suppressors (TVS diodes), clamp large voltage spikes by entering reverse conduction at a defined threshold.

Limitations and considerations include that excessive reverse voltage can permanently damage devices, and reverse leakage, which grows with temperature, can affect precision in sensitive circuits. Proper biasing and voltage ratings are essential for reliable operation.