BC549 is a bi-polar low noise general purpose NPN transistor that is commonly used in switching and amplifying applications. It can found in relay driver, LED driver and other medium power switching devices and audio or signal amplifiers. The features of the BC549 transistor are below:

• Continuous Collector Current: 100mA
• Collector Emitter Voltage: 30V
• Base Trigger Voltage: 5V
• Current Gain: 800 (max)
• Type: NPN (low noise)
• Package: TO-92

 Applications: 

• Switching small loads
• Used in audio noise filters
  
• Used in small signal amplifiers
  
• LED array sequence controller
• Darlington pair