Definition
A semiconductor PN junction connected to a voltage source so that the positive terminal is applied to the N-type material and the negative terminal to the P-type material. In this state, the junction blocks current flow except for a very small leakage current, because the applied voltage widens the depletion region at the boundary between the two materials.
Plain English
A junction inside a semiconductor that has been hooked up to a battery the 'wrong way around,' so almost no current can flow through it. It acts like a closed gate.
Context Anchor
Seen in aircraft electrical and avionics system descriptions, especially when explaining how electronic parts control or block current flow.
Derivation
Bias' here comes from the electrical sense of applying a steady voltage to push a component into a particular operating state. 'Reverse' means the voltage is applied opposite to the direction that would normally allow current to flow. Together: the junction is being pushed into its non-conducting state.
Why Pilots Care
Reverse-biased junctions are how diodes block current in one direction, which is the basis of rectifiers, voltage regulators, and protection circuits found throughout aircraft electrical systems. Understanding the concept helps when troubleshooting avionics failures or interpreting maintenance discussions.
Analogy
Think of a one-way door. Push it the right way and it swings open easily (forward bias). Push it the wrong way and it stays shut (reverse bias).
Intuition Check
Reverse-biased does not mean the part is installed backward. It means the voltage across the junction is applied in the direction that normally blocks current.
Example Sentence 1
When the diode is reverse-biased, it stops current from flowing back into the alternator and protects the circuit.
Example Sentence 2
A technician measures voltage across the junction to confirm it remains reverse-biased and prevents unwanted current in the circuit.