Description
The S8550 is a PNP bipolar junction transistor (BJT) commonly used for low-power switching and amplification. It is widely found in small electronic devices, Arduino projects, audio circuits, and signal control applications.
 
Basic Characteristics
Type: PNP Transistor
Collector-Emitter Voltage (Vceo): −25V to −40V
Collector Current (Ic): Up to −1.5A
Power Dissipation: Around 1W
Gain (hFE): 85 – 300 (depends on version)
Package: Usually TO-92
 
Pin Configuration (TO-92 Package)
If the flat side faces you and pins point downward:
Emitter
Base
Collector
⚠️ Always confirm using a datasheet or multimeter because pin order may vary slightly by manufacturer.
 
How It Works
Since it is a PNP transistor:
It turns ON when the base voltage is lower than the emitter voltage.
Current flows from Emitter → Collector when activated.
It is often used on the high side of a circuit.
 
Common Applications
Relay driver circuits
LED switching
Audio amplifier stages
Signal inversion
Power switching in small electronics
 
S8550 vs S8050
S8550 → PNP transistor
S8050 → NPN transistor
They are complementary pairs often used together in push-pull circuits.