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BD139 NPN Power Transistor

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by Ray

NPN medium-power transistor, 80 V / 1.5 A, in a TO-126 package for audio and driver stages.

transistorbjtnpnmedium-powerto-126st
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BD139

STMicroelectronics · Bipolar Transistor (BJT) · TO-126

The BD139 is an NPN medium-power transistor rated for 80 V and 1.5 A continuous collector current in a TO-126 package. It is widely used in audio amplifier output and driver stages, discrete linear regulators, and general medium-power switching. Its complement is the BD140 PNP.

Pinout

Pin Name Type Function
1 E passive Emitter terminal of the NPN BJT. Absolute maximum VEBO = 5 V. Typically returned to ground or a low-impedance node in common-emitter audio driver stages.
2 C passive Collector terminal of the NPN BJT. Absolute maximum VCEO = 80 V, VCBO = 80 V. Continuous IC = 1.5 A, peak ICM = 3 A. VCE(sat) ≤ 0.5 V at IC = 0.5 A, IB = 0.05 A. Collector tab is electrically common to the metal mounting tab of the SOT-32 package.
3 B input Base terminal of the NPN BJT. Absolute maximum base current IB = 0.5 A. Typical VBE ≈ 1 V at IC = 0.5 A, VCE = 2 V. Drives collector current via hFE (40-250 at IC = 150 mA).

Key specifications

Parameter Value
Type NPN medium-power transistor
Collector-emitter voltage (VCEO) 80 V
Collector current (IC) 1.5 A continuous (3 A peak)
DC current gain (hFE) 40 to 250
Transition frequency (fT) 190 MHz
Power dissipation 12.5 W
Operating temperature -55 C to 150 C

Ordering variants

  • BD139
  • BD139-10
  • BD139-16

CAD (KiCad official)

  • Symbol: bd139.kicad_sym
  • Footprint: bd139.kicad_mod
  • 3D model: TO-126 body from KiCad Package_TO_SOT_THT/TO-126-3_Vertical.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: STMicroelectronics datasheet (9 pp, sha256 9a72cdfa334700b8, retrieved 2026-08-17, tier: manufacturer)
  • Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF