(100PCS) BC557 PNP DIP Transistor

​1. Pinout (TO-92 Package)

​When you hold the transistor with the flat side facing you:

1. ​Collector (Left)
2. ​Base (Middle)
3. ​Emitter (Right)

​2. Example: Using BC557 as a Switch

​In this example, we use the BC557 to turn on an LED. Because it is a PNP transistor, the load is usually placed between the Collector and the Ground.

• ​Logic: When the Base is HIGH (5V), the “switch” is OFF. When the Base is LOW (0V/Ground), the “switch” is ON.

​Components:

• ​Voltage Source: 5V
• ​Resistor (R_B): 1k$\Omega$ (connected to the Base to protect it)
• ​LED + Resistor: 330$\Omega$ (connected to the Collector)

​The Circuit:

1. ​Connect the Emitter directly to the +5V rail.
2. ​Connect one end of a 1k$\Omega$ resistor to the Base. The other end goes to your switch or microcontroller pin.
3. ​Connect the Collector to the Anode (long leg) of the LED.
4. ​Connect the Cathode (short leg) of the LED to a 330$\Omega$ resistor, then to Ground.

​3. Example: Touch Switch (Darkness Sensor)

​Because the BC557 is sensitive, you can create a simple touch-activated circuit.

• ​Setup: Connect the Emitter to +9V. Connect a small LED and resistor to the Collector.
• ​Action: If you touch the Base and the Ground rail simultaneously with your finger, your body acts as a high-value resistor. This pulls the Base “low” enough to trigger the transistor and light the LED