The reverse breakdown voltage of the led is about 5 volts. Its forward volt ampere characteristic curve is very steep, and must be used in series to control the current through the pipe. The current-limiting resistance R can be calculated as follows:
R = (e-uf)/IF.
Where E is the power supply voltage, UF is the positive pressure drop of LED, IF is the general working current of LED. The longer one of the two leads of the light-emitting diode is the positive pole and should be the positive electrode of the power supply. Some leds are as long as two leads, but there is a protruding tongue on the shell, which is the positive pole near the small tongue.
Compared with small incandescent bulbs and neon lights, leds are characterized by low operating voltages (some only a few volts). The working current is very small (some of which are only a few milliamps to emit light); Good anti-impact and anti-seismic performance, high reliability and long life; The strength and strength of the luminescence can be easily modulated by the strength of the current through modulation. Because of these characteristics, light-emitting diodes are used as light sources in some photoelectric control devices and are used as signal displays in many electronic devices. Make a strip of the tube heart, and use 7 strips of light tubes to form a seven-section semiconductor digital tube (figure). Each digital tube can display 0-90 digits.
Red and yellow leds work voltage is 2 v, the other colors of working voltage is 3 v, the general working current of the light emitting diode are 20 ma, if pick up on the 5 v power supply, power supply electric reduce the working voltage of diode is partial pressure resistance to voltage, then use this working voltage divided by the diode current can calculate the resistance of the resistance. Such as 3 v diode (5-3) / 0.02 = 100 euro, 2 v diode (5-2) / 0.02 = 150 euro, but not all leds are working current 20 ma, some big and some small rectifier diode can also be used to actual use partial pressure, the pressure drop of a diode is 0.7 v, with three series to divide voltage is 2.1 v, the rest is just 3.1 v or by four series the rest 2.2 v
Limit current to 20ma, red light 1.2v, green light 1.4v.
Forward working current If: it refers to the forward current value of the light-emitting diode when it is normally glowing. Generally, the working current of LED light emitting diode is more than ten mA to dozens mA, while the working current of low current LED is below 2mA (brightness is the same as that of ordinary light emitting tube).
Forward working voltage VF: the working voltage shown in the general light-emitting diode parameter table is obtained from a given forward current. It is usually measured at IF=20mA. Leds are working voltage VF at 1.4 ~ 3V. When the outside temperature increases, VF will decrease.
R material V/I
In general, I = 3 ~ 5mA, then R =? .
Brightness and current are not linear relation. When the current is large enough, the brightness changes little. As long as the current exceeds the maximum forward current, it will burn. In particular, the general electric current is selected at 3-20ma.
To control the forward current of the light-emitting diode, one important parameter of the light-emitting diode must be known: the Vf value.