Light-emitting diodes are often used as display indicators, so many power indicator lights are displayed with light-emitting diodes, such as our product indicator lights, switch socket power indicator lights, and so on. Next, I will explain to you a conventional 5mm light-emitting diode. The role of this LED in the power indicator light, the size of this LED lamp bead is Ф5MM, and the standard LED lamp bead has a through hole. The maximum forward current IF=25mA, the maximum reverse voltage Vr=5V, and the forward working voltage Vf=1.7V.

1. In the DC power indicator; this is relatively simple as a DC power supply circuit and can be driven directly, only need to add a current limiting resistor, or scan mode. It should be noted that the current limiting resistor R≥(5V-Vf)/IF, Vf is the forward voltage drop, IF is the working current, where R must be at least greater than 132Ω, here is 1K ohm, the current is 5mA at this time, and the limit is current. The resistance should not be too large, otherwise it will affect the brightness. 2. In the AC power indicator; if AC input is used, a relatively simple circuit is to directly connect a current limiting resistor in series, but although such a circuit is simple and low in cost, the resistor consumes a lot of power, so the choice of resistor power is One problem, at this time, the current limiting resistor R≥220V/IF, because it is only used as an indicator, so the current will not be set very large.