Bipolar Junction Transistors (BJTs) use a weak signal (low current and/or voltage) to control a larger voltage and/or current. The switch circuit is the simplest BJT circuit.
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The 2N3904 is very popular NPN Bipolar Junction Transistor (BJT). Therefore, I use them in many of my videos.
The pin layout and direction of voltage and conventional current flow (positive to negative) is shown in the first diagram.
The NPN BJT collector must be able to handle the amount of current needed by the load. This maximum collector current (Ic) varies widely between different transistors. Always check the datasheet for the particular part number you are using to learn all it’s limitations.
The 2N3904 is rated at a maximum of 200mA collector current.
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