BD249C - 25A 100V NPN Power Transistor | onsemi | Amplifier/Switching
MPN: BD249C ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.85 | $2.85 |
| 10 | $2.56 | $25.60 |
| 100 | $2.28 | $228.00 |
| 500 | $2.05 | $1,025.00 |
| 1,000 | $1.82 | $1,820.00 |
BD249C Overview
A power BJT is a current-controlled semiconductor amplifier that uses a small base current to control a much larger collector current. Within the component hierarchy, the BD249C belongs to the NPN silicon power transistor family, a subset of bipolar junction transistors, which in turn fall under discrete power semiconductors used in power management and power conversion systems.
Key features include a 100 V VCEO rating (the C-suffix voltage class of the BD249 series), 25 A continuous collector current, and a transition frequency of 3 MHz, making it suitable for audio power amplifier output stages and general-purpose switching. The epoxy molding meets UL 94 V-0 at 0.125 inch thickness, and the device provides ESD robustness of greater than 400 V (Machine Model, class C) and greater than 8000 V (Human Body Model, class 3B). A Pb-free package option is available.
The BD249C is designed for complementary use with the BD250 series (PNP) at 25 degrees C case temperature, simplifying push-pull output stage design in linear amplifiers. Its high current gain and rugged safe operating area allow direct drive from driver stages in class-AB audio amplifiers, motor controls, and DC-DC converters.
Typical applications include general-purpose power amplification, linear power supplies, switching regulators, and motor drive circuits where high current and moderate voltage are required.
Design consideration: because power dissipation is rated at 125 W only with the case held at 25 degrees C, a substantial heatsink and thermally conductive interface are mandatory in real designs; derate linearly as case temperature rises.
This page synthesizes distributor pricing, drop-in alternatives, practical design notes, and comparison data not found in the manufacturer datasheet alone.
Drop-in alternatives for BD249C — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BD249C (same form factor and footprint) — differing in Flammability Rating, Package, Transistor Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
BD249B
✅ Drop-In📋 Reference alternative (not in catalog)
BD249A
✅ Drop-In📋 Reference alternative (not in catalog)
2SD1841
✅ Drop-In📋 Reference alternative (not in catalog)
2SD1842
✅ Drop-In📋 Reference alternative (not in catalog)
BD250C
✅ Drop-In📋 Reference alternative (not in catalog)
BD249C Maximum Ratings & Electrical Characteristics
| Polarity | NPN |
| Collector-Emitter Voltage (Vceo) | 100 V |
| Continuous Collector Current | 25 A |
| Peak Collector Current | 40 A |
| Power Dissipation (at 25 C case) | 125 W |
| Transition Frequency (ft) | 3 MHz |
| Complementary PNP Part | BD250 series |
| Package | SOT-93 (through hole) |
| Mounting Type | Through Hole |
| Transistor Type | Single Bipolar (BJT) |
| ESD Rating - Machine Model | > 400 V (Class C) |
| ESD Rating - Human Body Model | > 8000 V (Class 3B) |
| Flammability Rating | UL 94 V-0 @ 0.125 in |
| Lead-Free (Pb-Free) Package | Available |
BD249C Pin Configuration
| Pin 1 | Base — Base control terminal |
| Pin 2 | Collector — Collector, connected to case/tab for heatsinking |
| Pin 3 | Emitter — Emitter terminal |
Typical Applications
BD249C is suitable for 6 applications: Audio Power Amplifier Output Stage, Linear Power Supply Pass Element, Switching Regulator and DC-DC Converter, DC Motor Drive and Control, General-Purpose Power Switching, Inverter and UPS Output Stages.
Audio Power Amplifier Output Stage
The BD249C fits class-AB audio output stages because its 3 MHz transition frequency covers the audio band with ample loop-gain margin, and its 25 A / 125 W ratings support amplifiers driving low-impedance loads. In a complementary push-pull configuration, it pairs with the BD250C PNP at matched ratings, giving symmetric positive and negative half-cycles and low distortion. Emitter ballast resistors (typically 0.22 to 0.47 ohm) force current sharing between paralleled pairs, and the bias compensation transistor should be thermally coupled to the heatsink to prevent thermal runaway. Because the collector is the case, an insulated mounting kit is required when the heatsink is grounded.
Recommended
Linear Power Supply Pass Element
In series-regulated linear supplies, the BD249C serves as the series pass transistor, where its 100 V VCEO tolerates high raw-DC input rails and its 25 A rating supports high-current outputs. The base is driven by an error-amplifier driver stage; multiple BD249C devices can be paralleled with individual emitter resistors to share load current. Thermal design dominates here: dissipating VIN-VOUT times load current, the 125 W rating applies only at 25 degrees C case temperature, so a large finned heatsink with forced airflow is typically needed above 30-40 W. The SOT-93 case-collector simplifies mounting to a chassis-mounted heatsink with an insulation kit.
Recommended
Switching Regulator and DC-DC Converter
The BD249C operates as the power switch in buck, boost, and general-purpose switching converters up to roughly the 100 V input class. Its 3 MHz transition frequency supports switching at tens to low hundreds of kilohertz, where switching losses remain acceptable for a bipolar device. A base drive network with a speed-up capacitor and reverse-bias turn-off (or a Baker clamp) minimizes storage time and reduces switching loss. Snubbers across the collector-emitter terminals tame inductive voltage spikes well below the 100 V limit. Compared with a MOSFET, the BJT offers lower forward saturation voltage at very high currents, which benefits low-voltage, high-current converter stages.
Recommended
DC Motor Drive and Control
For DC motor drives, the BD249C handles the high inrush and stall currents typical of brushed motors, with its 40 A peak collector current rating absorbing startup transients. In H-bridge configurations, NPN BD249C devices form the low-side (and high-side with suitable drive) switches, while the BD250C complementary provides the opposite polarity devices. Flyback diodes must be placed across each device to clamp inductive kick from the motor windings below the 100 V rating. Linear servo amplifiers also use the BD249C as a pass device, where its robust safe operating area handles the simultaneous high voltage and high current during acceleration.
Recommended
General-Purpose Power Switching
As a general-purpose high-power NPN switch, the BD249C controls heaters, solenoids, lamps, and relays drawing several amps from supply rails up to 100 V. Driven into saturation with base current around one-tenth of collector current, its collector-emitter saturation voltage stays low, minimizing on-state dissipation. The UL 94 V-0 rated epoxy package and strong ESD ratings (greater than 400 V MM, greater than 8000 V HBM) improve assembly-line robustness. The through-hole SOT-93 leads accept high currents without heavy PCB copper, and the case-collector mounting allows direct chassis attachment for heatsinking in industrial control panels and test equipment.
Recommended
Inverter and UPS Output Stages
In square-wave and modified-sine inverters and small UPS output stages, the BD249C switches the transformer primary, where its 100 V rating covers 12 V and 24 V battery systems with wide transient margin and its 25 A current rating supports hundreds of watts of output power. Push-pull inverter topologies use the BD249C on one leg and the complementary BD250C on the other, driven alternately at line frequency. Robust ESD ratings and the UL 94 V-0 flame-retardant package suit the electrically harsh automotive and standby-power environment. Parallel pairs with emitter-sharing resistors extend power capability while keeping per-device dissipation within thermal limits.
Recommended
Recommended Products Summary
Engineering reference data for BD249C — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BD249B | BD249A | 2SD1841 | 2SD1842 | BD250C |
|---|---|---|---|---|---|---|
| Package | SOT-93 | SOT-93 - same | SOT-93 - same | SOT-93 - same | SOT-93 - same | SOT-93 - same |
| Brand | onsemi | onsemi | onsemi | Toshiba | Toshiba | onsemi |
| Polarity | NPN | NPN | NPN | NPN | NPN | PNP (complement) |
| Pin Compatibility | B-C-E, case = collector | Identical | Identical | SOT-93 compatible, verify datasheet | SOT-93 compatible, verify datasheet | Identical (PNP complement) |
Key Differentiators
- Highest voltage class in the BD249 family (vs BD249B)
- Factory-matched complementary PNP available (vs 2SD1841)
- Higher ratings than legacy TO-3 substitutes (vs 2N3055)
Design Notes
The 125 W dissipation figure applies only with the case at 25 degrees C. Estimated: dissipating 40 W with a heatsink-plus-insulator junction-to-ambient path of 2 C/W at 40 degrees C ambient yields roughly 40 + 80 = 120 degrees C junction temperature, near typical BJT limits. Size the heatsink for worst-case dissipation at your maximum ambient, and use thermal grease or a phase-change pad across the case-collector. Derate power linearly as case temperature rises.
Because the collector is electrically the case in the SOT-93 package, any grounded heatsink requires a mica or silicone insulator plus a shoulder washer. Keep base and emitter leads short to minimize parasitic inductance in switching layouts. Paralleled devices need individual low-ohm emitter ballast resistors (typically 0.1 to 0.47 ohm) to force current sharing, since VBE matching alone is insufficient across a paralleled array.
Do not exceed the 100 V VCEO when switching inductive loads - a flyback/snubber clamp is mandatory for motors, solenoids and transformer primaries. In switching service, bipolar storage time extends turn-off delay; use a reverse base drive or Baker clamp if switching frequency and losses matter. For audio stages, mount the VBE multiplier or bias compensation transistor on the same heatsink as the BD249C to track temperature and prevent thermal runaway.
Compliance Information
onsemi datasheet states Pb-free package is available and epoxy meets UL 94 V-0 @ 0.125 in. Formal RoHS/REACH declarations depend on the exact ordering code; confirm with onsemi for the purchased suffix.
