Electrical engineering
Power, semiconductors, digital
Transformers, three-phase, diodes, gates.
Basics
Transformer
AC only. Turns ratio sets voltage. Ideally power is conserved: V₁ I₁ = V₂ I₂. Transmission uses high V and low I to cut I²R loss.
Semiconductors
Diode: current one way. Transistors (BJT, MOSFET): a small signal controls a larger current — amplify or switch. Logic gates are MOSFET switches in combination.
Digital basics
AND, OR, NOT are primitive. NAND/NOR are functionally complete. Binary, bits. Sampling theorem: sample faster than twice the highest frequency to reconstruct (ideal case).
Formulas
Ideal transformer
Voltage follows turns; current is inverse.
Symbols
-
Nturns
Three-phase power (balanced)
Line voltage and line current. cosφ is the power factor.
Symbols
-
V_Lline-to-line voltage -
cosφpower factor
Decibel (power)
Use 20 log₁₀ for voltage at the same impedance. +3 dB is twice the power.
Nyquist (ideal)
Sampling frequency must exceed twice the highest frequency in a band-limited signal.
Symbols
-
f_ssampling frequency
Key table
| Korea mains | single-phase 220 V, 60 Hz (nominal) |
|---|---|
| Resistor color (4-band) | digit, digit, multiplier, tolerance |
In this field
DC circuits
Ohm, Kirchhoff, series/parallel, power.
Capacitors, inductors, AC
Charge/discharge, reactance, impedance, resonance.
Magnetism, motors, control
Faraday, motors, filters, feedback.
Signals and logic
Fourier sketch, sampling, Boolean algebra.
Semiconductors
Carriers, diodes, a MOSFET sketch.
Measurements and electrical safety
Multimeters, RMS versus peak, transformer ratio, and electrical safety.
Op-amps and filters
The ideal op-amp, inverting and non-inverting gain, RC low- and high-pass, cutoff frequency.
Digital logic
Boolean algebra, gates, flip-flops, and timing.
Three-phase power
Line versus phase, Y and Δ, √3 power, and a motor sketch.
Batteries and photovoltaics
Capacity and C-rate, series/parallel packs, PV I–V curves, and the maximum-power point.