Electronic Fundamentals

Silicon and germanium are doped to form N-type (extra electrons) and P-type (holes) material. A PN junction forms a diode: it conducts when forward biased (~0.6 V for silicon, ~0.3 V for germanium) and blocks when reverse biased until breakdown.

Half-wave rectifiers use one diode; full-wave bridge rectifiers use four and give smoother output. Zener diodes operate in reverse breakdown to regulate voltage. Other types: LED, photodiode, Schottky (fast switching, low drop) and varistors used for transient suppression.

Bipolar junction transistors (NPN/PNP) are current-controlled: a small base current controls a large collector current (gain hFE = Ic/Ib). FETs and MOSFETs are voltage-controlled with very high input impedance. Transistors work as amplifiers (linear region) or switches (saturation/cut-off).

ICs pack many devices onto one chip. The operational amplifier has very high open-loop gain, high input impedance and low output impedance; negative feedback sets the closed-loop gain. Common configurations: inverting, non-inverting, voltage follower, summing and comparator.

PCBs consist of copper tracks bonded to an insulating substrate, single-, double- or multi-layer. Handle with ESD precautions — wrist strap, grounded mat and conductive bags. Repairs are limited to those authorised by the CMM; conformal coating must be restored after any rework.

A servo is a closed-loop system: a command is compared with feedback to produce an error signal that drives the actuator until the error is nulled. Components include synchros, resolvers, LVDTs, RVDTs, E&I bars and rate gyros. Key faults: hunting (oscillation, excess gain), sluggishness (excess damping) and standing error.