Diodes
Diode symbols, characteristics and properties; half-wave and full-wave rectification; smoothing; clippers and clampers; Zener, Schottky, photodiode, varactor, LED, thyristor and varistor devices.
Diodes — summary notes
Free- A diode conducts from anode to cathode in the direction of the symbol's arrow. The painted BAND marks the cathode.
- Forward volt drop is about 0.7 V in silicon. PIV (peak inverse voltage) is the maximum reverse voltage the diode can withstand.
- Half-wave rectification uses one diode and produces ripple at the SUPPLY frequency.
- Full-wave rectification — centre-tap (2 diodes) or bridge (4 diodes) — produces ripple at TWICE the supply frequency, which is easier to smooth.
- A reservoir/smoothing capacitor across the output reduces ripple by holding charge between peaks.
- Special diodes: Zener (operates in reverse breakdown for voltage regulation), LED (emits light), photodiode (light-sensitive), Schottky (fast switching, low drop), varactor (voltage-variable capacitance), SCR/thyristor (gate-latched), varistor (surge suppression).
- ⚠ Exam trap: bridge and full-wave ripple is 2f; half-wave is 1f. The band marks the cathode. A Zener works in REVERSE breakdown.
- Silicon forward drop
- ≈ 0.7 V per junction
- Half-wave ripple
- f_ripple = f_supply
- Full-wave / bridge ripple
- f_ripple = 2 × f_supply
- Bridge output (ideal)
- V_dc ≈ 0.637 × V_peak (unsmoothed)
A full-wave bridge rectifier is fed from a 400 Hz aircraft supply. What is the ripple frequency?
Full-wave rectification gives ripple at twice the supply frequency: 2 × 400 = 800 Hz.
How many diodes does a bridge rectifier use, and how many conduct at any instant?
Four diodes in a bridge; two conduct in each half cycle, in diagonally opposite pairs, so the load current always flows the same way.
Diode rectifier — half & full wave
FreeSmoothing filter & ripple
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Zener voltage regulator
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Diode clipper
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Diodes concept map
FreeDiodes
Diodes quiz
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