2N5551 — 160V 600mA High-Voltage NPN Bipolar Junction Transistor (TO-92)

Overview

The 2N5551 (and its surface-mount version MMBT5551) is a high-voltage NPN bipolar junction transistor manufactured by onsemi, Fairchild, STMicroelectronics, and Central Semiconductor. Housed in a through-hole TO-92 plastic package with standard Emitter - Base - Collector (E-B-C) pinout, it is a staple component in electronics assortment kits when higher breakdown voltages are needed.

Rated for a collector-emitter breakdown voltage ( $V_{CEO}$ ) of $160\text{V}$ ( $180\text{V}$ $V_{CBO}$ ) and a continuous collector current of $600\text{ mA}$ , the 2N5551 is engineered for circuits operating far beyond the $40\text{V}$ limit of the standard 2N3904. It is widely used in discrete audio power amplifier differential input and voltage amplifier stages (VAS), high-voltage logic level shifters, telecom line interfaces, relay drivers on 48V telecom/industrial rails, and linear regulator pass-transistor pre-drivers.

Quick reference


Transistor Type	High-Voltage Small-Signal NPN BJT
Package	TO-92 (3-pin through-hole) / SOT-23 (MMBT5551)
Collector-Emitter Voltage ( $V_{CEO}$ )	$160\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$180\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$600\text{ mA}$ max
DC Current Gain ( $h_{FE}$ )	$80$ to $250$ ( $I_C = 10\text{mA}, V_{CE} = 5.0\text{V}$ )
Transition Frequency ( $f_T$ )	$100\text{ MHz} \dots 300\text{ MHz}$
Total Power Dissipation ( $P_D$ )	$625\text{ mW}$ ( $T_A = 25^\circ\text{C}$ )
Complementary PNP Pair	2N5401 (160V PNP)
Operating Temp Range	$-55^\circ\text{C}$ to $+150^\circ\text{C}$

Pinout (TO-92 Package - E-B-C Standard)

Looking at the flat front face with leads pointing downward:

text

        ┌─────────┐
        │  TO-92  │
        │ 2N5551  │
        └─┬───┬───┬─┘
          1   2   3
          E   B   C

Pin	Name	Type	Description
1	`EMITTER`	Emitter Terminal	Emitter (Connect to ground or emitter degeneration resistor)
2	`BASE`	Base Terminal	Base control input (Driven with current via series base resistor)
3	`COLLECTOR`	Collector Terminal	Collector output (Connected to switched high-voltage load or supply rail)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	160	—	—	V	$I_C = 1.0\text{mA}, I_B = 0$
Collector-Base Breakdown	$V_{(BR)CBO}$	180	—	—	V	$I_C = 100\ \mu\text{A}, I_E = 0$
Emitter-Base Breakdown	$V_{(BR)EBO}$	6.0	—	—	V	$I_E = 10\ \mu\text{A}, I_C = 0$
Collector Cutoff Current	$I_{CBO}$	—	—	50	nA	$V_{CB} = 120\text{V}, I_E = 0$
DC Current Gain	$h_{FE}$	80	—	250	—	$I_C = 10\text{mA}, V_{CE} = 5.0\text{V}$
DC Current Gain	$h_{FE}$	30	—	—	—	$I_C = 50\text{mA}, V_{CE} = 5.0\text{V}$
Collector Saturation Voltage	$V_{CE(sat)}$	—	—	0.20	V	$I_C = 50\text{mA}, I_B = 5.0\text{mA}$
Base Saturation Voltage	$V_{BE(sat)}$	—	—	1.00	V	$I_C = 50\text{mA}, I_B = 5.0\text{mA}$

Typical Application: High-Voltage 48V/100V Relay Driver / Level Shifter

text

                       +48V Industrial / Telecom DC Rail
                                    │
                            [ + Relay Coil - ]
                                    │
                                    ├───[ 1N4007 High-Voltage Flyback Diode ]───┐
                                    │   (Anode to Collector, Cathode to +48V)   │
                              [Pin 3: COLLECTOR]                                │
                                  2N5551                                        │
  MCU GPIO (3.3V / 5.0V)      [Pin 2: BASE]                                     │
          │                         │                                           │
          ├───[ 2.2kΩ Resistor ]────┤                                           │
          │                         ├───[ 10kΩ Base Pull-Down Resistor ]────────┤
         GND                        │                                           │
                              [Pin 1: EMITTER]                                  │
                                    │                                           │
                                   GND ─────────────────────────────────────────┴─── Common GND

Comparison: 2N5551 vs 2N3904 vs MPSA42

Parameter	2N3904	2N5551	MPSA42
$V_{CEO}$ Breakdown	$40\text{ V}$	$160\text{ V}$	$300\text{ V}$
Max Current ( $I_C$ )	$200\text{ mA}$	$600\text{ mA}$	$500\text{ mA}$
Gain ( $h_{FE}$ )	$100 \dots 300$	$80 \dots 250$	$40 \dots 200$
Transition Freq ( $f_T$ )	$300\text{ MHz}$	$100 \dots 300\text{ MHz}$	$50\text{ MHz}$
Complementary PNP	2N3906	2N5401	MPSA92

Common mistakes

Exceeding the 6V reverse emitter-base breakdown voltage ( $V_{EBO}$ ): Like most BJTs, applying more than $-6.0\text{V}$ between base and emitter causes zener breakdown and irreversibly degrades transistor current gain.
Using 2N3904 formulas for base drive in 100V switching circuits: In high-voltage switching, ensure adequate base drive current ( $I_B \approx I_C / 10$ ) so the transistor saturates fully to $V_{CE(sat)} \le 0.2\text{V}$ , preventing thermal destruction under load.

Notes

Suffix Guide: 2N5550 is a $140\text{V}$ rated variant; 2N5551 is the full $160\text{V}$ part; MMBT5551 is the SOT-23 surface-mount equivalent.

Interface	Current-Driven Base Junction
Package	TO-92 Plastic (through-hole) / SOT-23 (MMBT5551)