Hardware & Devicesconcept · 4 min · updated Jun 28, 2026
Transistors
By HealthAtoms Editorial (AI-assisted draft)Awaiting expert review
A tiny electrically-controlled switch and amplifier — the single invention everything digital is built from, and the part that drives a motor or amplifies an ECG.
In one line
A transistor lets a small signal control a large one. As a switch it turns things on/off with no moving parts; as an amplifier it makes a weak signal bigger. Billions of them, etched microscopically, make a processor.
<figure style="text-align:center;margin:1.5rem 0"> <svg viewBox="0 0 240 140" role="img" aria-label="NPN transistor symbol with base, collector and emitter" style="width:100%;max-width:280px;height:auto;color:var(--c-iot)"> <line x1="20" y1="70" x2="70" y2="70" stroke="currentColor" stroke-width="2"/><text x="14" y="62" font-size="11" fill="var(--text-3)" text-anchor="end">base</text> <line x1="70" y1="40" x2="70" y2="100" stroke="currentColor" stroke-width="5"/> <line x1="70" y1="55" x2="120" y2="25" stroke="currentColor" stroke-width="2"/><line x1="120" y1="25" x2="120" y2="12" stroke="currentColor" stroke-width="2"/><text x="132" y="20" font-size="11" fill="var(--text-3)">collector</text> <line x1="70" y1="85" x2="120" y2="115" stroke="currentColor" stroke-width="2"/><polygon points="104,103 116,109 106,114" fill="currentColor"/><line x1="120" y1="115" x2="120" y2="128" stroke="currentColor" stroke-width="2"/><text x="132" y="124" font-size="11" fill="var(--text-3)">emitter</text> </svg> </figure>How it works
A small current or voltage on the control terminal (the base of a BJT, the gate of a MOSFET) decides how much current flows through the other two.
- Switch — fully on or off. An MCU pin switches a transistor that drives a motor, pump or bright LED.
- Amplifier — held in between, a small input wiggle becomes a large output wiggle — how millivolt biosignals get boosted.
Where it shows up in digital health
- Every chip is millions-to-billions of transistor switches.
- Driving actuators — a transistor / H-bridge lets a low-power controller switch an infusion-pump motor.
- Front-end amplification of ECG/EMG starts with transistors (packaged as an op-amp).
Watch for
A MOSFET power switch must be sized for the current and kept cool — a hot, under-rated switch is a common failure point in motor and heater circuits.