Electronic Fundamentals: DC and AC Circuits, Components, and Semiconductors
DC circuits
Ohm's law (V = IR), power (P = VI = I squared R = V squared / R), and Kirchhoff's voltage and current laws underlie most items. Resistors in series add; in parallel the reciprocals add. Voltage dividers set bias and reference levels, but a meter's own resistance loads the circuit and can mislead you.
AC and reactive components
Sinusoids are described by peak, peak-to-peak, RMS, and average values; for a sine wave, RMS = 0.707 x peak and peak = 1.414 x RMS. Capacitive reactance X_C = 1/(2 pi f C) falls as frequency rises; inductive reactance X_L = 2 pi f L rises with it. Impedance combines resistance and reactance as a phasor, Z = square root of (R squared + X squared) when only one reactance is present. Series resonance, f = 1/(2 pi times the square root of LC), gives minimum impedance; parallel resonance gives maximum. Q describes how sharply a tuned circuit discriminates.
Transformers
Turns ratio sets voltage and current: V secondary / V primary = N secondary / N primary, and impedance transforms as the square of the turns ratio. Transformers pass AC only, which is why they appear in power supplies and audio rather than DC paths.
Semiconductors
A silicon diode conducts above about 0.7 V forward and blocks in reverse until breakdown, the basis of rectifiers, clippers, and zener regulators. A BJT is current-controlled (beta = collector current / base current); a FET is voltage-controlled at the gate. Know the three configurations: common emitter/source (voltage gain, phase inversion), common base/gate (low input impedance), common collector/drain (buffer, gain near 1).
Rule of thumb: halve the capacitance and the capacitive reactance doubles.