Passive Components
Resistors, capacitors, inductors — the building blocks
Resistor (fixed)
Resistor
A component that limits current and divides voltage by providing a fixed opposition (resistance) to current flow. The most common part in any circuit.
Potentiometer / Rheostat / Trimmer
Resistor
A three-terminal resistor with an adjustable wiper that allows manual control of resistance. Used for volume controls, tuning, and adjustable circuit parameters.
Resistor Array / Network
Resistor
Several resistors of the same value in one package sharing a common pin or arranged as isolated pairs. Saves board space and guarantees the resistors match each other closely.
Thermistor (NTC / PTC)
Resistor (non-linear)
A temperature-sensitive resistor whose resistance changes significantly with temperature. NTC types decrease resistance with heat; PTC types increase resistance with heat.
Varistor / MOV
Resistor (non-linear)
A voltage-dependent resistor that protects circuits from voltage surges by dramatically increasing resistance when voltage exceeds a threshold.
Photoresistor (LDR)
Resistor (non-linear)
A light-dependent resistor whose resistance decreases with increasing light intensity. Used to detect light levels or create light-sensitive circuits.
Capacitor (ceramic / MLCC)
Capacitor
Stores energy in an electric field. Ceramic caps are small, cheap, non-polarised, and the workhorse for filtering and decoupling.
Capacitor (aluminium electrolytic)
Capacitor
A polarised capacitor that packs a lot of capacitance into a small can, using a thin oxide layer as the dielectric. The default choice for power-supply smoothing and bulk energy storage.
Capacitor (tantalum)
Capacitor
A polarized capacitor that uses tantalum metal for its electrodes, offering high capacitance per volume and stable performance. Commonly used in power supply filtering and timing circuits.
Capacitor (film)
Capacitor
A capacitor using a plastic film dielectric. Non-polarised, very stable, low loss and self-healing — the go-to choice for audio, timing, snubbers and anything touching mains.
Supercapacitor
Capacitor
An electrochemical capacitor with enormous capacitance — whole farads in a coin-sized can. Sits between capacitors and batteries: charges in seconds, delivers brief bursts of power, survives a million cycles.
Inductor / Coil
Inductor
A passive component that stores energy in a magnetic field when current flows through it, opposing changes in current flow. Used for filtering, tuning, and energy storage.
Choke / Common-mode Choke
Inductor
An inductor used to block AC while passing DC. A common-mode choke has two windings on one core that cancel for the wanted signal but present high impedance to noise flowing the same way down both wires.
Ferrite Bead
Inductor
A tiny ferrite cylinder or SMD chip that turns high-frequency noise into heat while passing DC almost unhindered. Behaves like a frequency-dependent resistor, not a pure inductor.
Transformer (power)
Transformer
A device that transfers electrical energy between circuits through electromagnetic induction, changing AC voltage and current levels while maintaining frequency.
Current / Potential Transformer (CT/PT)
Transformer
Transformers built for measurement, not power. A CT (current transformer) steps a large current down to a measurable one; a PT/VT steps a high voltage down. They let meters and relays watch big circuits safely.
Quartz Crystal / Resonator
Timing
A passive component that uses the piezoelectric effect of quartz to provide a precise frequency reference for oscillators in timing circuits.
Crystal Oscillator (XO/TCXO)
Timing
A complete clock source in a can: crystal, drive circuit and output buffer together. Feed it power and it outputs a clean square wave — no fussing with load capacitors like a bare crystal.