How to find the right BJT Transistors AI guide

onsemi: Classic general-purpose and power BJTs in many packages.
Nexperia: Large range of small-signal BJTs in SMD and TO-92 packages.
STMicroelectronics: Power BJTs in TO-220 and TO-247.
Diodes Incorporated: Small-signal SMD BJTs.
Toshiba: Bipolar transistors, including audio complementary pairs.

Written by an AI model from its trained knowledge.

What the AI looks for in BJT Transistors

Collector-emitter voltage (Vceo): Vceo must be comfortably above the supply voltage, plus any inductive kickback if no flyback diode is fitted. Breakdown is the most common way BJTs die in switching circuits.
Current gain at your operating current: Read hFE at your actual collector current. For saturated switching, design for forced gain well below the datasheet minimum (about 10 to 20 is a common rule). hFE varies widely with current, temperature and unit-to-unit spread, and the headline figure is often the best case.
Saturation voltage: Check Vce(sat) at your collector current and base drive. Vce(sat) sets the switching losses and how much voltage the load actually receives.
Power dissipation and package: Small TO-92 or SOT-23 parts only suit low-power duty. Use TO-220 or TO-247 with a heatsink for watts of dissipation, and check the safe operating area for linear use. Dissipation limits and second breakdown in linear operation cap usable current well below the maximum collector current.
Transition frequency (fT): For amplifiers, fT should be far above your signal bandwidth. Gain falls off as frequency approaches fT.
Polarity and pinout: Match NPN or PNP to the circuit and confirm the pin order in that specific maker's datasheet. TO-92 pin orders differ between manufacturers, even for the same part number.

Pin order for the same part number can differ between manufacturers. Check the datasheet for the exact maker before soldering.