Resistor Types and the Spec Most BOMs Skip

Full article on JLCPCB: https://jlcpcb.com/blog/complete-guide-to-resistor-types

Tolerance is a day-one, room-temperature number. TCR is what you actually live with. A ±1% resistor at 200 ppm/°C can move another ±1% across a 50 °C rise, so its real in-circuit accuracy is worse than its label — and TCR is the column most engineers never filter on.

Resistor types chart — fixed, variable and non-linear families with their symbols

Three Families

Every resistor sorts into one of three branches. Fixed types hold a value, judged on tolerance, TCR and power. Variable types expose a wiper, judged on track material and rotational life. Non-linear types are transducers — read the curve, not a tolerance figure.

· Carbon film: ±2% to ±5%, TCR −200 to −1000 ppm/°C

· Metal film: ±0.1% to ±1%, TCR ±25 to ±100 ppm/°C

· Thick film chip: ±1% to ±5%, TCR ±100 to ±200 ppm/°C

· Thin film chip: ±0.05% to ±0.5%, TCR ±5 to ±25 ppm/°C

· Wirewound: ±0.005% to ±5%, 1 W to 300 W and beyond

· Metal foil: ±0.001% to ±0.01%, TCR 0.2 to 2 ppm/°C

Classification tree from fixed, variable and non-linear down to each resistor type

The 200-Cycle Trap

Track material sets the quality, but the specification nobody prints is rotational life. A panel potentiometer is rated for 10,000 to 1,000,000 cycles. A trimmer is often rated for 200. Put a trimmer behind a user-accessible knob and the track wears through inside a year, and a worn track produces a scratchy, intermittent, open-circuit wiper that gets blamed on everything except the pot. Trimmers are set-once parts; a 25-turn cermet trimmer exists to null an offset and then be left alone.

Choosing Fast

Work five filters in order and you finish choosing between two parts, not twenty. Fix value and tolerance first, rounding to a stocked E-series value under IEC 60063 — E24 for ±5%, E96 for ±1% and tighter. Size power at worst-case I²R and pick a part rated for at least twice it, because ratings are quoted at 70 °C ambient and fall from there. Filter on TCR before tolerance whenever the resistor sets a measured quantity. Surge-exposed inputs get metal oxide or thick film, never thin film.

The five-step resistor type selection flowchart

The full resistor types chart, all seven fixed families and the application-by-application selection table are in the complete guide: Read the full guide