S8550 — PNP Low-Voltage High-Current Bipolar Junction Transistor

Overview

The S8550 (SS8550) is a low-voltage, high-current PNP bipolar junction transistor (BJT) manufactured by Micro Commercial Components (MCC), Changjiang Electronics, and generic semiconductor foundries. Packaged in a compact TO-92 enclosure, it is ubiquitous in low-cost consumer electronics, toys, and beginner Arduino / Raspberry Pi component starter kits.

Optimized for high-current low-voltage switching, the S8550 handles continuous collector currents up to $-700\text{ mA}$ (peak pulsed currents up to $-1.5\text{ A}$ ) at collector-emitter voltages up to $-25\text{ Volts}$ . It is the direct PNP complementary transistor to the S8050.

Quick reference


Transistor Type	Low-Voltage High-Current PNP BJT
Package	TO-92 (Flat face front, leads pointing down)
Collector-Emitter Voltage ( $V_{CEO}$ )	$-25\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$-40\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$-700\text{ mA}$ continuous ( $-1500\text{ mA}$ peak)
DC Current Gain ( $h_{FE}$ )	120 to 400 (Ranks: B: 120–200, C: 160–300, D: 200–400)
Transition Frequency ( $f_T$ )	$150\text{ MHz}$ min
Power Dissipation ( $P_D$ )	$625\text{ mW}$ ( $T_A = 25^\circ\text{C}$ )

Pinout (TO-92 Package)

Looking at the flat face of the TO-92 package with leads pointing down:

text

        ┌─────────────┐
        │    S8550    │  (Flat Package Face)
        └─┬───┬───┬───┘
          1   2   3
          E   B   C

Pin	Name	Description
1	`EMITTER` (`E`)	Emitter terminal (High-side power rail $+V_{CC}$ )
2	`BASE` (`B`)	Base terminal (Active LOW control input via base resistor)
3	`COLLECTOR` (`C`)	Collector terminal (Load output connection)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Voltage	$V_{CEO}$	-25	—	—	V	$I_C = -1\text{mA}, I_B = 0$
Collector Cutoff Current	$I_{CBO}$	—	—	-100	nA	$V_{CB} = -35\text{V}, I_E = 0$
DC Current Gain (Rank D)	$h_{FE}$	200	—	400	—	$V_{CE} = -1\text{V}, I_C = -50\text{mA}$
DC Current Gain ( $I_C=500\text{mA}$ )	$h_{FE}$	50	—	—	—	$V_{CE} = -1\text{V}, I_C = -500\text{mA}$
Collector Saturation Volts	$V_{CE(sat)}$	—	-200	-600	mV	$I_C = -500\text{mA}, I_B = -50\text{mA}$

Common mistakes

Exceeding $-25\text{V}$ collector breakdown voltage: The S8550 is specifically a low-voltage PNP transistor ( $V_{CEO} = -25\text{V}$ ). Do not use it on $36\text{V}$ or $48\text{V}$ power rails; use a 2N2907A ( $-60\text{V}$ ) or BC327 ( $-45\text{V}$ ) instead.
Forgetting base current limiting resistor: Always place a series resistor between the MCU pin and the S8550 Base to limit base current.

Notes

S8550 vs S8050: S8550 is PNP (high-side switch); S8050 is its complementary NPN pair (low-side switch). Both offer $700\text{ mA}$ current capacity in TO-92.