The BC817‑Q series are industry‑classic NPN surface‑mount small‑signal transistors manufactured by silicon epitaxial planar process. They adopt the popular miniature SOT‑23 surface‑mount package with individual dimensions of 2.9 mm × 1.3 mm × 1.0 mm and a weight of only 0.008 g. The suffix “Q” denotes AEC‑Q101 automotive‑electronic reliability qualification. The 16Q / 25Q / 40Q share identical base electrical parameters such as voltage rating and current rating, differing only in DC current gain hFE. They rank among the most widely‑used surface‑mount general‑purpose NPN transistors for consumer electronics, industrial‑control equipment and automotive power supplies. Paired with its complementary BC807‑Q series, they can construct push‑pull amplifiers, H‑bridge drivers and symmetric power‑control circuits.
Key Specifications
Collector‑Emitter Breakdown Voltage BVCEO > 45 V; BVCBO > 50 V; BVEBO > 5 V. Suitable for 12 V / 24 V low‑voltage DC systems with sufficient voltage margin to withstand back‑EMF surges from inductive loads.
Continuous Collector Current IC = 0.5 A. Moderate current rating, optimized for low‑power precision devices.
Peak Pulse Current ICM = 1 A, designed as twice the continuous collector current, providing certain immunity against power‑on inrush surges.
Collector Dissipation Power Pc = 300 mW, suited for low‑power applications.
Saturation Voltage VCE(sat) < 0.7 V @ 0.5 A. Low saturation voltage yields low conduction loss and mild temperature rise.
Transition Frequency fT > 100 MHz. Excellent high‑frequency response for distortion‑free audio amplification and smooth response in low‑speed switching circuits.
DC Current Gain hFE (VCE = 1 V, IC = 100 mA):
16Q: 100 ~ 250. Optimal linearity for signal amplification, minimum noise and stable quiescent operating point.
25Q: 160 ~ 400. Mainstream industry variant, balancing current‑drive capability and signal linearity. Best compatibility and minimum hardware‑debugging effort; preferred for general‑purpose selection.
40Q: 250 ~ 600. Ultra‑high current gain at the cost of narrower linear range under heavy‑current conditions; not recommended for high‑precision audio amplification.
Output Capacitance Cob = 10 pF. Low capacitance for favorable high‑frequency performance.
Typical Applications
BC817‑16Q (Low‑Gain Precision Variant)
Preamplification of small audio signals for Bluetooth earphones and portable speakers
Precision conditioning and acquisition of weak voltage signals from various sensors
BC817‑25Q (General‑Purpose Variant, Widest Application Coverage)
Auxiliary low‑voltage power switching for set‑top boxes, routers and small‑home‑appliance control boards
Microcontroller I/O port power expansion; drivers for small relays and buzzers
PWM dimming for LED light strips; level conversion between 3.3 V and 5 V logic signals
BC817‑40Q (Ultra‑High‑Gain Low‑Power Variant)
Full‑load small‑signal driving for 3.3 V microcontrollers
Amplifying circuits for under‑voltage and over‑charge detection in power banks and energy‑storage power supplies
Low‑power sleep‑wake switches and high‑sensitivity trigger circuits for battery‑powered devices
Speed regulation for miniature DC motors
