Electronic Components and Semiconductor Devices
Domain 2: Electronic Components and Semiconductor Devices
This section checks identification, polarity, package recognition, and basic testing of passive components, diodes, transistors, and ICs. Expect color codes, SMD codes, datasheet limits, and DMM diode/continuity tests.
Core rules
- Four-band resistor: digit, digit, multiplier, tolerance. Gold = ±5%, silver = ±10%, brown = ±1%. Five-band adds a third digit.
- SMD resistor codes: 472 = 47 × 10² = 4.7 kΩ; 000 = 0 Ω jumper; R47 = 0.47 Ω.
- Diode: anode positive, cathode band. Silicon forward drop about 0.6–0.7 V; Schottky 0.2–0.4 V; LED 1.8–3.3 V depending on color. Reverse bias should read open.
- BJT: NPN turns on with base about 0.7 V above emitter; PNP with base about 0.7 V below emitter. Check junctions with diode test, not resistance mode.
- MOSFET: gate is insulated; use ESD care. Check body diode and look for gate-source short. ICs: notch or dot marks pin 1; observe absolute maximum ratings and supply polarity.
Worked example
A four-band resistor reads yellow-violet-red-gold. Yellow = 4, violet = 7, red multiplier = ×100, gold = ±5%. Value = 47 × 100 = 4.7 kΩ, tolerance 235 Ω, so acceptable range 4.465–4.935 kΩ. A DMM reads 4.62 kΩ, which is inside range. If it read 462 Ω, suspect a multiplier error or wrong part; if open, check crack or bad solder.
Traps
- Reading the tolerance band as a digit, especially gold/silver.
- Testing a diode in-circuit and being misled by parallel paths; lift one leg when unsure.
- Confusing NPN and PNP base polarity.
- Assuming all 3-pin packages have the same pinout.
- Ignoring ESD damage that leaves a marginal, not dead, device.