The terminal voltage of the PN junction constitutes a certain barrier. When the forward bias voltage is applied, the barrier decreases, and the majority carriers in the P and N regions diffuse toward each other. Since the electron mobility is much larger than the hole mobility, a large amount of electrons diffuse into the P region, which constitutes injection of minority carriers in the P region. These electrons recombine with the holes on the valence band, and the energy obtained during recombination is released as light energy. This is the principle of PN junction illumination.
1. Voltage: LED lamp bead uses low voltage power supply, the supply voltage is between 2-4V, depending on the product, so it is driven by a higher voltage than the high voltage power supply; it is especially suitable for public places;
2. Current: The working current is between 0 and 15 mA, and the brightness becomes brighter as the current increases.
3. Performance: Energy consumption is reduced by 80% compared to incandescent lamps with the same efficacy.
4. Applicability: Very small, each unit LED small piece is a square of 3-5mm, so it can be prepared into various shapes of devices, and is suitable for a variable environment.
6. Response time: The response time of the incandescent lamp is millisecond, and the response time of the LED lamp is nanosecond.
7. Environmental pollution: no harmful metal mercury.
8. Color: Change the current to change color. The light-emitting diode can easily adjust the energy band structure and band gap of the material through chemical modification method to realize multi-color luminescence of red, yellow, green and blue. For example, a red LED with a small current can change to orange, yellow, and finally green as the current increases.
1, brightness
LED lamp beads have different brightness and different prices.
Lamp beads: general brightness is 60-70lm; bulb lamp: general brightness is 80-90lm.
1W red light, the brightness is generally 30-40lm; 1W green light, the brightness is generally 60-80lm; 1W yellow light, the brightness is generally 30-50lm; 1W blue light, the brightness is generally 20-30lm.
Note: 1W brightness is 60-110lm; 3W brightness is up to 240lm; 5W-300W is integrated chip, with serial/parallel package, mainly see how much current, voltage, several strings and several.
LED lens: The primary lens is generally made of PMMA, PC, optical glass, silica gel (soft silica gel, hard silica gel). The larger the angle, the higher the light efficiency. With a small angle LED lens, the light should be shot far.
2, wavelength
The wavelengths are the same and the colors are the same. The price is high.
White light is divided into warm colors (color temperature 2700-4000K), white (color temperature 5500-6000K), cool white (color temperature 7000K or more) Europeans prefer warm white.
Red light: Band 600-680, of which 620, 630 is mainly used for stage lights, and 690 is close to infrared.
Blu-ray: Band 430-480, of which 460,465 stage lights are used more.
Green light: Band 500-580, of which 525, 530 stage lights are used more.
3. LEDs with different illumination angles have different illumination angles. Special lighting angle, the price is higher.
4, anti-static ability anti-static ability of the LED lamp beads, long life, and therefore high prices. LED lamp beads with an antistatic greater than 700V are usually used for LED lighting. 5. Leakage current LED lamp bead is a unidirectional conductive illuminator. If there is reverse current, it is called leakage, and LED lamp bead with large leakage current has short life and low price.
The parameters of the resistor are generally two, the resistance value R and the power P.
R=(U-Uled)/Iled, the standard voltage of USB is DC5V, so R=(5-Uled)/Iled
Uled, the positive conduction voltage of the lamp bead. Iled, the positive conduction current of the lamp bead.
There are many types of LEDs, different colors, and generally different currents.
The size of the resistor affects the current, which in turn affects the brightness of the lamp bead. However, as long as the forward maximum current is not exceeded, it can be used, but the brightness is different, so the selection range is relatively large.
Resistance power P=Iled*Iled*R
example:
Low power red and yellow, its resistance = voltage / current = 1.8 / 0.02 = 90Ω,
Low power blue-green, its resistance = voltage / current = 3.2 / 0.02 = 160Ω,
High power red and yellow, its resistance = voltage / current = 2.2 / 0.35 = 6Ω,
High power blue-green, its resistance = voltage / current = 3.4 / 0.35 = 10Ω.
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