Electronic Components
Master Guide

Resistors limit current flow and create voltage drops according to Ohm's Law (V = IR). They are used for biasing transistors, voltage division, current limiting for LEDs, pull-up/pull-down duties, and impedance matching. Their value is measured in Ohms (Ω), kΩ, or MΩ.

Capacitors store and release electrical energy in an electric field between two conductive plates separated by a dielectric. They block DC while passing AC signals, filter power supply noise, couple AC stages, set timing in RC circuits, and provide bypass/decoupling functions. Value measured in Farads (F), µF, nF, pF.

A P-N junction semiconductor that allows current to flow in one direction (forward bias) and blocks it in the other (reverse bias). Used for rectification (AC→DC), voltage clamping, protection against reverse polarity, signal demodulation, and as voltage references (Zener). Forward voltage drop: Si ≈ 0.6–0.7V, Schottky ≈ 0.2–0.4V, Ge ≈ 0.3V.

A BJT is a current-controlled semiconductor device. A small base current (IB) controls a much larger collector current (IC), with the ratio known as the current gain (hFE or β, typically 100–500). Used as amplifiers in analogue circuits and as electronic switches in digital logic, motor drivers, and relay drivers. NPN: common emitter switch; PNP: high-side switch.

A MOSFET is a voltage-controlled transistor. Gate voltage (VGS) controls the channel conductivity between Drain and Source. N-channel: positive VGS turns it ON. P-channel: negative VGS turns it ON. Key advantage over BJT: extremely high input impedance (gate), very fast switching, and low on-resistance (RDS(on)). Widely used in SMPS, H-bridges, and logic-level switching.

An inductor stores energy in a magnetic field created by current flowing through its coil. It opposes changes in current (inertia effect). In DC circuits, it acts as a low-resistance path; at AC/high frequencies, it presents high impedance (XL = 2πfL). Used in switched-mode power supplies (buck/boost converters), EMI filters, RF tuning circuits, and chokes to block AC noise on DC lines. Measured in Henrys (H), mH, µH.

Transformers transfer AC energy between two or more electrically isolated windings through a shared magnetic core. The voltage ratio equals the turns ratio: V1/V2 = N1/N2. Used for mains power adaptation, galvanic isolation, impedance matching in audio, gate drive isolation in SMPS, and current transformers for measurement. Only work with AC — will saturate on DC.

An IC integrates thousands to billions of transistors, resistors, and other components onto a tiny silicon die. Types range from simple logic gates and op-amps to complex microprocessors and SoCs. All ICs require correct supply voltage(s), ground connections, and usually decoupling capacitors on their supply pins. The internal circuitry performs amplification, comparison, logic operations, signal conversion (ADC/DAC), communication, and control.

Voltage regulators maintain a stable, controlled output voltage from a varying input. Linear regulators (e.g., 7805, LM317, AMS1117) dissipate excess voltage as heat — simple but inefficient. Switching regulators (buck, boost, buck-boost) use inductors and capacitors with PWM switching for high efficiency (85–95%). LDO (Low Dropout) regulators work with very small input-output differences.

A relay uses an electromagnet (coil) energized by a control current to mechanically move an armature, switching one or more sets of contacts. This provides complete electrical isolation between the low-voltage control circuit and the switched load circuit. Types: SPDT, DPDT, latching, solid-state (SSR — uses a triac or MOSFET internally). Used for mains switching, automotive, industrial control, and protection circuits.

A quartz crystal exploits the piezoelectric effect — mechanical vibration at a precise resonant frequency when AC voltage is applied. Used with an oscillator amplifier circuit (internal to microcontrollers, or an external inverter gate) to produce a highly stable clock frequency. TCXO (temperature-compensated) and VCXO (voltage-controlled) variants offer higher stability. Crystal oscillator modules contain the crystal plus oscillator circuit and output a square wave directly.

Fuses sacrifice themselves — a wire element melts and opens the circuit when current exceeds rated value. PTC (Polyfuse) resettable fuses increase resistance dramatically when heated by overcurrent, limiting current until the fault is removed, then self-reset. TVS Diodes (Transient Voltage Suppressors) clamp voltage spikes to a safe level in nanoseconds, protecting sensitive ICs from ESD and inductive kickback. All are critical for reliable, safe circuit design.