What is transistor, Emergency lighting, NPN transistor, transistor circuit

MMBT Series 40 V 200 mA SMT NPN Silicon General Purpose Transistor – SOT-23

• Website URL: https://www.futureelectronics.com/p/semiconductors--discretes--transistors--bipolar-transistors/smmbt3904lt1g-onsemi-3162400
• Country List: Bangladesh