Transistor Circuit to Drive LED

A transistor used as a switch may easily drive a Light Emitting Diode (LED). Usually an NPN transistor in a common emitter circuit is used. Since the current requirement of the diode is usually small, almost any general-purpose transistor works as the driver. The transistor still has to behave as a switch and operate in the saturation region. You will need to find two resistor values. There is the series resistance value for the resistor in series with the LED, and there is the base resistor value.

An LED has a forward voltage parameter, which you may find from the reference sheet or measure it using a digital meter. Then use the links below to calculate the values.

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