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Newbie here. I bought a couple BC547B transistors to build some logic gates. I'm using a breadboard which is connected to the 3.3V and ground from my UNO Elegoo R3 controller.

I connected an LED to the emitter of the transistor. It lit up once I connect the power supply with the base pin, even though the collector was disconnected. I have followed this other thread and connected a high resistor (tried 100K and 1M) between base and emitter, which makes the LED glow really dim. Once I connected the collector it lighted up very bright again.

My question is: How can I fix this issue? Ideally I want to LED to not light up at all unless there is current on the collector. I already made sure that the transistor pins are two lanes apart each, but that did not help.

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    \$\begingroup\$ Draw a schematic. \$\endgroup\$
    – Andy aka
    Commented Jul 19, 2020 at 14:16
  • \$\begingroup\$ in addition to the schematic, as Andy mentions, you can also include a picture of your breadboard. The schematic does not have to be a real working (simulation) schematic, we just need to see some sort of drawing. Hand drawing is often also good. \$\endgroup\$
    – P2000
    Commented Jul 19, 2020 at 14:37

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Reset to default
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My question is: How can I fix this issue? Ideally I want to LED to not light up at all unless there is current on the collector.

Move the LED to be in the collector circuit (with the appropriate series current limiting resistor) and connect the BC547 emitter to ground/0 volts. Feed the base via a 1 to 10 kohm series resistor.

As you currently have it connected, the base-emitter junction acts like a forward biased diode and will supply the LED with current via the base. With the above proposal this won't happen.

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