BD139 — 80V 1.5A Medium-Power NPN Bipolar Junction Transistor (TO-126)

Overview

The BD139 is an iconic 80V 1.5A medium-power complementary silicon NPN bipolar junction transistor manufactured by STMicroelectronics, onsemi, and NXP. Housed in a through-hole TO-126 (SOT-32) plastic package with a central mounting screw hole, it has achieved legendary status across the audio engineering and DIY enthusiast community.

Featuring a collector-emitter breakdown voltage ( $V_{CEO}$ ) of $80\text{V}$ , a continuous collector current rating of $1.5\text{A}$ ( $3.0\text{A}$ peak pulse), a high transition frequency ( $f_T$ ) of $190\text{ MHz}$ , and linear gain across a broad current range, the BD139 (paired with its PNP complement BD140) is the gold standard for hi-fi audio power amplifier push-pull driver stages, discrete Class-A headphone amplifiers (e.g. JLH 1969 / Lehmann clones), active Vbe multiplier thermal bias servos, and linear laboratory power supplies.

Quick reference


Transistor Type	Medium-Power Complementary Silicon NPN BJT
Package	TO-126 / SOT-32 (3-pin through-hole with mounting hole)
Collector-Emitter Voltage ( $V_{CEO}$ )	$80\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$80\text{ V}$ max ( $100\text{ V}$ peak)
Continuous Collector Current ( $I_C$ )	$1.5\text{ A}$ max ( $3.0\text{ A}$ peak pulse)
Base Current ( $I_B$ )	$0.5\text{ A}$ max
DC Current Gain ( $h_{FE}$ )	$40$ to $250$ (BD139-10: 63–160, BD139-16: 100–250)
Transition Frequency ( $f_T$ )	$190\text{ MHz}$ typ ( $> 50\text{ MHz}$ min)
Power Dissipation ( $P_D$ )	$12.5\text{ Watts}$ ( $T_C = 25^\circ\text{C}$ with heatsink) / $1.25\text{ W}$ in free air
Complementary PNP Pair	BD140 (80V PNP)

Pinout (TO-126 / SOT-32 Package - E-C-B Standard)

Looking at the printed front face of the TO-126 package with leads pointing downward:

text

        ┌───────────────┐
        │   O [Mount]   │
        ├───────────────┤
        │     BD139     │
        └─┬─────┬─────┬─┘
          1     2     3
          E     C     B

Pin	Name	Type	Description
1	`EMITTER`	Emitter Terminal	Emitter (Connect to ground, emitter resistor, or output node)
2	`COLLECTOR`	Collector Terminal	Collector (Connected to positive supply rail or load; internally tied to tab)
3	`BASE`	Base Terminal	Base control input (Driven with base current via audio VAS stage or resistor)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	80	—	—	V	$I_C = 10\text{mA}, I_B = 0$
Collector-Base Breakdown	$V_{(BR)CBO}$	80	—	—	V	$I_C = 100\ \mu\text{A}, I_E = 0$
Emitter-Base Breakdown	$V_{(BR)EBO}$	5.0	—	—	V	$I_E = 10\ \mu\text{A}, I_C = 0$
Collector Cutoff Current	$I_{CBO}$	—	—	100	nA	$V_{CB} = 30\text{V}, I_E = 0$
DC Current Gain ( $h_{FE}$ )	$h_{FE}$	40	—	250	—	$I_C = 150\text{mA}, V_{CE} = 2.0\text{V}$
DC Current Gain ( $h_{FE}$ )	$h_{FE}$	25	—	—	—	$I_C = 500\text{mA}, V_{CE} = 2.0\text{V}$
Collector Saturation Voltage	$V_{CE(sat)}$	—	—	0.50	V	$I_C = 500\text{mA}, I_B = 50\text{mA}$
Base Saturation Voltage	$V_{BE(sat)}$	—	—	1.00	V	$I_C = 500\text{mA}, I_B = 50\text{mA}$

Typical Application: Complementary Push-Pull Audio Buffer (Class AB)

text

                            +15V to +24V Positive Supply Rail
                                          │
                                   [Pin 2: COLLECTOR]
                                      BD139 (NPN)
  Audio Input (from Op-Amp)        [Pin 3: BASE]
           │                              │
           ├───[ 1N4148 Diode Bias 1 ]────┤
           │                              │
           │                       [Pin 1: EMITTER]
           │                              │
           │                              ├───[ 0.47Ω 2W Emitter Resistor ]───┐
           │                                                                  ├────► Audio Output (Speaker / Headphones)
           │                              ┌───[ 0.47Ω 2W Emitter Resistor ]───┘
           │                       [Pin 1: EMITTER]
           │                              │
           └───[ 1N4148 Diode Bias 2 ]────┤
                                      BD140 (PNP)
                                   [Pin 3: BASE]
                                          │
                                   [Pin 2: COLLECTOR]
                                          │
                            -15V to -24V Negative Supply Rail

Comparison: BD139 vs TIP31C vs 2N2222A

Parameter	2N2222A	BD139	TIP31C
Package	TO-92 / TO-18	TO-126 (Heatsinkable)	TO-220
$V_{CEO}$ Voltage	$40\text{ V}$	$80\text{ V}$	$100\text{ V}$
Max Current ( $I_C$ )	$600\text{ mA}$	$1.5\text{ A}$	$3.0\text{ A}$
Transition Freq ( $f_T$ )	$300\text{ MHz}$	$190\text{ MHz}$	$3\text{ MHz}$
Audio Linearity	Moderate	Excellent (Hi-Fi Standard)	Power Only

Common mistakes

Misidentifying the E-C-B pinout: Unlike TO-92 American parts (E-B-C), TO-126 transistors have the Collector in the center (Emitter - Collector - Base).
Mounting to a heatsink without electrical insulation: The metal rear backing tab of the TO-126 is internally bonded to Pin 2 (Collector). In split-rail audio amplifiers, connecting the collector tab directly to an earthed chassis heatsink will short out the power rail. Use a mica or sil-pad insulator and nylon mounting washer.

Notes

Vbe Multiplier Thermal Tracking: The central mounting hole allows the BD139 to be bolted directly on top of main output power transistors (2N3055 / 2SC5200) to provide thermal feedback that eliminates thermal runaway.

Interface	Current-Driven Base Junction
Package	SOT-32 / TO-126 (3-pin through-hole with mounting hole)