BD135 — 45V 1.5A Medium-Power NPN Bipolar Junction Transistor (TO-126)

Overview

The BD135 is a classic 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 an integrated central mounting screw hole, it provides a rugged, heatsinkable alternative to small-signal TO-92 transistors.

Rated for a collector-emitter voltage ( $V_{CEO}$ ) of $45\text{V}$ , a continuous collector current of $1.5\text{A}$ ( $3.0\text{A}$ peak pulse), a transition frequency ( $f_T$ ) of $190\text{ MHz}$ , and up to $12.5\text{ Watts}$ of power dissipation when heatsinked, the BD135 is widely used in audio amplifier pre-driver and driver stages, medium-current relay and solenoid drivers, linear power supply series-pass elements, and discrete H-bridge motor controllers.

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 ( $V_{CEO}$ )	$45\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$45\text{ V}$ max
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 $250$ (BD135-10: 63–160, BD135-16: 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	BD136 (45V 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]   │
        ├───────────────┤
        │     BD135     │
        └─┬─────┬─────┬─┘
          1     2     3
          E     C     B

Pin	Name	Type	Description
1	`EMITTER`	Emitter Terminal	Emitter (Connect to ground or negative supply rail)
2	`COLLECTOR`	Collector Terminal	Collector (Connected to switched load; internally bonded to rear metal tab)
3	`BASE`	Base Terminal	Base control input (Driven with base current via series resistor)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	45	—	—	V	$I_C = 10\text{mA}, I_B = 0$
Collector-Base Breakdown	$V_{(BR)CBO}$	45	—	—	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 Circuit: 12V 1A High-Power Relay / Lamp Driver

text

                       +12V DC Supply
                             │
                     [ + High-Current Load / Relay - ]
                             │
                             ├───[ 1N4007 Flyback Diode ]──────────┐
                             │   (Anode to Collector, Cathode to +12V)
                       [Pin 2: COLLECTOR]                          │
                            BD135                                  │
  MCU GPIO (3.3V / 5V) [Pin 3: BASE]                               │
          │                  │                                     │
          ├───[ 330Ω - 1kΩ ]─┤                                     │
          │                  ├───[ 10kΩ Base Pull-Down Resistor ]──┤
         GND                 │                                     │
                       [Pin 1: EMITTER]                            │
                             │                                     │
                            GND ───────────────────────────────────┴─── Common GND

Comparison: BD135 vs BD137 vs BD139

Parameter	BD135	BD137	BD139
$V_{CEO}$ Voltage	$45\text{ V}$	$60\text{ V}$	$80\text{ V}$
Max Current ( $I_C$ )	$1.5\text{ A}$	$1.5\text{ A}$	$1.5\text{ A}$
Transition Freq ( $f_T$ )	$190\text{ MHz}$	$190\text{ MHz}$	$190\text{ MHz}$
Complementary PNP	BD136	BD138	BD140

Common mistakes

Assuming TO-92 (E-B-C) pinout: The TO-126 BD135 uses the European standard Emitter - Collector - Base (E-C-B) sequence from left to right. Swapping the base and collector leads is the most common assembly error.
Operating above 1W without a heatsink: While the silicon die is rated for 12.5W, in free air without a heatsink the package can only dissipate 1.25W before exceeding safe junction temperatures. Mount to a small aluminum clip-on or stamped heatsink for loads $> 500\text{mA}$ .

Notes

Gain Grouping: Sub-grades are marked on the package: -6 ( $h_{FE} = 40 \dots 100$ ), -10 ( $h_{FE} = 63 \dots 160$ ), and -16 ( $h_{FE} = 100 \dots 250$ ).

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