Semiconductor Components Guide — Transistors, Diodes & ICs Explained

1. What are Semiconductors?

Semiconductors are crystalline materials (primarily silicon) with electrical conductivity between conductors (like copper) and insulators (like glass). By introducing controlled impurities through a process called doping, silicon forms P-type (positive hole carriers) and N-type (negative electron carriers) materials.

When a P-type and N-type region meet, they create a PN junction — the fundamental building block of all modern diodes, transistors, integrated circuits, and computer processors.

2. Diodes Explained: Rectifiers, Signal & Zener Diodes

A diode is an electrical one-way check valve that allows current to flow from anode to cathode when forward-biased, while blocking current in reverse:

3. Transistor Types: BJT vs. MOSFET

Transistors act as electronically controlled switches and current amplifiers:

• Bipolar Junction Transistors (BJTs): Current-controlled devices. Supplying a small base current ($I_b$) switches on a much larger collector-emitter current ($I_c$). Common maker standard: 2N2222 / 2N3904 (NPN) and 2N3906 (PNP).
• Field-Effect Transistors (MOSFETs): Voltage-controlled devices with near-infinite gate impedance. Applying a gate-source voltage ($V_{gs}$) opens a conductive channel between drain and source without drawing continuous gate current. Ideal for high-efficiency DC motor and high-power LED switching.

4. Testing Semiconductors with a Digital Multimeter

Use your multimeter's Diode Test mode to diagnose working semiconductors:

1. Silicon Diode Test: Red probe to Anode, Black probe to Cathode. Expect $0.55 ext{V} - 0.70 ext{V}$. Reverse probes: expect "OL" (Over Limit / Open Circuit).
2. NPN Transistor Test: Place Red probe on the Base. Touch Black probe to Collector, then Emitter. Both should read a forward PN drop ($0.6 ext{V} - 0.7 ext{V}$). Any short circuit ($0.0 ext{V}$) indicates a blown transistor.