Electronic Fundamentals
What the module tests
Electronic fundamentals covers semiconductor theory, diodes, rectifiers, transistors, printed circuit boards and servomechanisms. The emphasis is on how components behave in aircraft circuits, not on deep device physics.
Core rules
- A silicon diode conducts with about 0.6-0.7 V forward drop and blocks in reverse until breakdown.
- A half-wave rectifier produces one pulse per cycle; a full-wave bridge produces two and uses four diodes.
- In a bridge rectifier, two diodes conduct in series, so the DC peak is the AC peak minus about 1.4 V.
- A bipolar transistor has base, collector and emitter; small base current controls larger collector current.
- A servomechanism is a closed-loop system: command, error detector, amplifier, actuator and feedback.
Worked example
A transformer gives 12 V RMS to a bridge rectifier feeding a light load. Find the approximate peak DC voltage. AC peak = 12 × 1.414 = 16.97 V. In a bridge, two diodes are in the conduction path, so subtract 2 × 0.7 = 1.4 V. Peak DC ≈ 16.97 - 1.4 = 15.6 V. With a smoothing capacitor and light load, the output approaches this peak; under heavy load it falls toward the average.
Traps
Subtracting only one diode drop in a bridge; using RMS instead of peak; assuming the output is exactly the peak under load; confusing PNP and NPN current directions; treating a servo as an open-loop actuator; ignoring heat-sink requirements.
Exam approach
Identify the rectifier type first, then apply the correct diode-drop count. For transistor circuits, check bias polarity and whether the device is being used as a switch or an amplifier.