BJT vs. FET: Key Differences & When to Use Each Transistor
BJT (Bipolar Junction Transistor) uses both electrons and holes to carry current and needs a small base current to control a larger collector current. FET (Field-Effect Transistor) relies on an electric field to modulate a single charge carrier—electrons or holes—using virtually zero gate current.
Beginners swap them because both amplify, but datasheets and schematics look alike. Makers pick FETs for low-power Arduino boards, then wonder why their audio preamp hisses—the culprit is the wrong transistor type.
Key Differences
BJTs: current-controlled, ~0.7 V turn-on, higher gain, lower input impedance. FETs: voltage-controlled, ~1–4 V threshold, near-zero gate current, high input impedance, faster switching, lower noise.
Which One Should You Choose?
Audio preamps and analog amps love BJT’s linear gain. Switch-mode supplies, microcontrollers, and battery gadgets prefer FET’s efficiency and low drive power. Match load current, speed, and heat budget.
Can I swap a BJT for a FET in the same circuit?
Rarely. Biasing networks, drive voltage, and current paths differ; redesign is usually needed.
Which one is easier for beginners?
FETs—no base resistor calculations and less heat when switching LEDs or motors.