The magical effect of LED light-emitting diodes

LED light-emitting diode

Since the advent of LEDs, in most applications, it has been used as an indicator light. Now introduce a few typical uses.

(1) Three-terminal regulator 7805 application circuit, adding 1 LED can increase the output voltage and double as the power indicator, as shown in the figure below.

(2) LED is used in 220V, 50Hz mains, as the electrical work instruction or fuse blow indication, as shown in the right figure below.

In the AC working circuit, the current limiting resistor R can be calculated by:

R=(VE-UF)/21F

Where VE is the rms voltage of the AC power supply (AC220V), UF is the forward voltage drop of the LED. IF is the general operating current of the LED.