![]() Due to this biasing current, 2N3904 goes to the saturation state and the LED turns ON. When the switch is closed, the base of the transistor is biased, and current flows to the base of the transistor. Due to this, 2N3904 remains in the cut-off state and the LED does not glow. And no current flows to the base of the transistor. When the switch is open, the base of the transistor is not biased. The required resistor value can be easily calculated using Ohm’s law. Proper biasing of the base ensures adequate base current to turn ON the transistor.Ī resistor of 220 Ohm is connected between the load(LED) and the collector terminal to protect the LED from overcurrent. It is designed for low current and power, medium voltage, and can operate at moderately high speeds. The base of the transistor is biased using a 10 K Ohm resistor(R3) in parallel to the 1 K Ohm resistor(R2) plus base-emitter junction resistance(in series). The 2N3904 is a common NPN bipolar junction transistor used for general-purpose low-power amplifying or switching applications. The complete circuit is powered via a 5 V supply. In the circuit diagram given above, 2N3904 is used as a switch to turn ON/OFF an LED connected at the collector terminal.
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