BJT vs MOSFET: Key Differences & When to Use Each
BJT is a current-controlled three-layer transistor; MOSFET is a voltage-controlled field-effect switch. One needs base current, the other only gate voltage to turn on.
Beginners grab whichever part is in the drawer, then wonder why the amplifier squeals or the motor stalls—mixing control styles confuses datasheets and schematics alike.
Key Differences
BJT: 0.7 V base-emitter drop, lower input impedance, linear amplification. MOSFET: gate isolated by oxide, near-zero gate current, excels at fast switching and power handling.
Which One Should You Choose?
Use BJT for low-noise analog audio and precise current mirrors. Pick MOSFET for efficient DC-DC converters, high-speed PWM, or when driving heavy loads from tiny logic pins.
Examples and Daily Life
Your phone charger IC uses MOSFETs to sip 5 W with minimal heat. The vintage Walkman headphone stage relies on BJTs to keep hiss low while amplifying millivolts of music.
Can I parallel BJTs and MOSFETs?
Yes, but BJTs need ballast resistors; MOSFETs share naturally thanks to positive temperature coefficient.
Why do some circuits use both?
Designers combine them: MOSFET for switching, BJT for buffering, gaining the best of each world.