4.2 Semiconduc tor Diodes

• The semiconductor diode and its operation (forward and reverse bias)
• The characteristic curve of a diode
• Types of diodes (rectifier, LED, Zener) and rectification
• Testing and selecting diodes

• describe the operation of a semiconductor diode
• explain the characteristics of a diode (forward and reverse bias)
• identify types of diodes and their applications
• test a diode and construct a simple rectifier circuit
• appreciate the importance of diodes in electronics

“How does a diode work, and why is it important?”

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1. Semiconductor diodes
   40 min · 1 practice tasks · quiz
   How a diode (a single PN junction) works as a one-way valve for current, forward and reverse bias, its characteristic curve, rectifying AC into DC, the main types of diode, and why diodes are important.
2. Diode structure, terminals and symbol
   40 min · 1 practice tasks · quiz
   A diode is one PN junction in a package: anode (P), cathode (N), cathode band, and the arrow-and-bar symbol.
3. Forward bias: how a diode conducts
   40 min · 1 practice tasks · quiz
   Positive to the anode reduces the barrier; after about 0.7 V (silicon) current flows. Always include a series resistor.
4. Reverse bias: how a diode blocks
   40 min · 1 practice tasks · quiz
   Positive to the cathode widens the depletion region so almost no current flows, until the reverse rating is exceeded.
5. Turn-on voltage: silicon, germanium and LED
   40 min · 1 practice tasks · quiz
   Vf is about 0.7 V for silicon, 0.3 V for germanium, and 1.8 to 3.3 V for LEDs. Below Vf the diode is still off.
6. The diode characteristic curve
   40 min · 1 practice tasks · quiz
   An I-V graph with four regions: forward cut-off, forward conduction after the knee, reverse leakage, and reverse breakdown.
7. Plotting a diode characteristic in the workshop
   40 min · 1 practice tasks · quiz
   A practical: variable DC, series resistor, voltmeter across the diode, milliammeter in series; record, plot, reverse, stay below breakdown.
8. Rectifier diodes and their ratings
   40 min · 1 practice tasks · quiz
   The ordinary power diode (1N4001-1N4007): average forward current If and peak inverse voltage PIV, used to turn AC into DC.
9. Half-wave rectification
   40 min · 1 practice tasks · quiz
   One diode passes only the positive half of AC, giving pulsing DC at 50 Hz. Simple, but it wastes the other half.
10. Full-wave bridge rectification
    40 min · 1 practice tasks · quiz
    Four diodes, two conducting each half cycle, and why the bridge beats half-wave on every measure that matters.
11. Smoothing and ripple
    40 min · 1 practice tasks · quiz
    How a reservoir capacitor fills the gaps, what ripple is, and the trade-off that stops you simply fitting a huge capacitor.
12. The complete DC power supply
    40 min · 1 practice tasks · quiz
    The four stages put together, what each one does to the waveform, and why none of them can be left out.
13. Light emitting diodes
    40 min · 1 practice tasks · quiz
    How an LED differs from an ordinary diode, why it always needs a series resistor, and how to calculate that resistor.
14. Zener diodes
    40 min · 1 practice tasks · quiz
    A diode designed to break down safely, how it holds a voltage steady, and how the series resistor is chosen.
15. Testing a diode with a meter
    40 min · 1 practice tasks · quiz
    The diode test range, what each reading means, the four possible outcomes, and why a diode must be tested out of circuit.
16. Where diodes are used, and why they matter
    40 min · 1 practice tasks · quiz
    Six applications resting on one property, and the answer to the inquiry question.