(25PCS) BD 139 ORIGINAL NPN Transistor

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1. ​Base (Pin 3): Connect this to your control signal (like an Arduino pin) through a 1k$\Omega$ resistor. This limits the current so you don’t damage the transistor.
2. ​Collector (Pin 2): Connect this to the Negative (-) wire of your 12V LED strip.
3. ​Emitter (Pin 1): Connect this directly to the Ground (GND) of your power supply.
4. ​Power: Connect the Positive (+) wire of the LED strip to your 12V power source