The main part of the LED is also a PN junction, but after the LED is turned on, its voltage drop is generally about 2V, and some LEDs can reach 3V. The voltage drop of ordinary diodes is about 0.5V, such as Schottky diodes.
Light emitting diodes are generally used as indicators. For example, the power indicator and the communication indicator, for example, when the serial port is sending and receiving data, the LED flashes to indicate that the data is being sent and received.
In circuit design, a current limiting resistor should be connected in series. How to determine the value of the current limiting resistance? First, we should know the forward voltage and current of LED. The forward voltage of a certain LED is 2.5V, and the forward current is 5mA. This forward current has a value range. If the current is too large, the diode may be burned. If the current is too small, the brightness of the LED is not enough.
These parameters can be found in the LED Data Book.
Assume that the DC voltage is 5V. Subtract the diode voltage drop of 2.5V from 5V. The remaining 2.5V is divided by the current of 5mA. The resistance is equal to 500 ohms.
Therefore, a 500 ohm resistance is required in series in the circuit.
