Diodes in Action

Rectification and Power Conversion

The most fundamental diode application is rectification — converting AC (alternating current) to DC (direct current). Every power adapter you own uses diodes for this purpose.

• Half-wave rectifier: One diode passes only the positive half of the AC cycle
• Full-wave bridge rectifier: Four diodes arranged so both halves of the AC cycle produce positive output

Other critical diode applications:

• Protection diodes: Prevent reverse voltage from damaging circuits
• Voltage regulation: Zener diodes maintain a constant voltage (breakdown voltage)
• Signal clamping: Limit voltage swings in signal processing circuits

LEDs and Photodiodes

LEDs (Light-Emitting Diodes) are forward-biased PN junctions made from direct-bandgap materials. When electrons and holes recombine, they emit photons with energy equal to the bandgap:

• Red LEDs: GaAs/AlGaAs (bandgap ~1.8 eV, wavelength ~650 nm)
• Blue/Green LEDs: InGaN (bandgap ~2.5–3.0 eV)
• White LEDs: Blue LED + yellow phosphor coating

Photodiodes are the reverse — a reverse-biased junction where incoming photons generate electron-hole pairs in the depletion region, producing current proportional to light intensity. Your phone's camera sensor contains millions of photodiodes.