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. 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 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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