Some common knowledge of LED light source in engineering application

Note the basic characteristics and the use of LED.

1 photoelectric properties

The current LED flows in its current limits within the parameters of LED, the higher its brightness. The brightness of the LED with the LED is directly proportional to the current. But the green and blue and white saturation phenomenon occurs in the case of high current, not only the luminescence efficiency is greatly reduced, and the service life is will be shortened.

2 optical properties

LED divided by the color red, orange, yellow, green, blue, purple, white and other colors. Brightness divided by general light, bright, super bright, the same chip in different packages, it is not the same brightness. According to the human vision can be divided into visible light and the invisible light. Can be divided into monochrome, color, color and other types according to the number of luminous color. The color purity of the different prices vary greatly, the pure white LED price expensive. At the same time, light from different angles of view, light effect is also different, with special attention.

3 LED electrical properties common

(1) LED positive voltage

Different colors LED forward current at rated conditions, with different forward voltage drop value, red, yellow, green and blue: 1.8~2.5V, 2.7~4.0V. For the same color LED, the forward voltage drop and the light intensity is not entirely consistent:

LED model: 54HCA

Light color appearance color wavelength lambda D (nm) positive voltage VF brightness Iv (MCD)

IF=20mA

Min.Max.

Red transparent water 645~6601.82.550~300

Yellow green transparent water 570~5751.82.550~300

Yellow transparent water 585~5901.82.5500~5000

Blue transparent water 455~4752.74.0500~7000

Green transparent water 515~5352.74.02000~10000

Blue green water transparent 490~5152.74.02000~10000

White transparent water -2.74.03000~15000

Should try to use the forward voltage drop under rated current value of the same intensity range of small LED. the only way to ensure the luminous effect of LED on the same circuit. Each product packaging provides the specific electrical parameters according to different packaging plant spectral parameter tag value. Some companies (each batch sorting do not agree)

(2) rated current LED

Rated current LED different LED current ordinary 20mA, LED high current power is generally 40mA or 350mA range. Specific to the current parameters according to the packaging factory to provide value. The general LED in reverse voltage reverse current: VR=5V,: IR = 10 A.

(3) LED power

LED power varies, 70mW, 100mW, 1W, 2W, 3W, 5W and so on, must be chosen according to the LED, the number of circuits and configure the appropriate LED reasonable design, make it satisfy the LED power ratings, if the design of the circuit to make each LED too high voltage or current sharing will seriously affect the service life of the LED even burned LED, if the share of low voltage or current excitation of LED light intensity is not enough, can not give full play to the effect of LED should not reach our expectations.

4 temperature characteristics

(1) LED welding temperature should be below 250 DEG C, the welding time is controlled in the range of 3~5S. The LED temperature is too high to avoid damage to the chip.

(2) the brightness of the LED output and the temperature is inversely proportional to the temperature not only affect the brightness of the LED, but also affect its life. Try to reduce circuit heat use, and do some heat treatment.

5 anti-static properties

LED assembly process must strengthen the anti-static measures, because the operation process and the human body itself will produce static electricity, two electrode of the LED for the most vulnerable to static reverse breakdown, which seriously affect the service life of the LED and even completely scrapped.

Such as anti-static environment is not very perfect, can add anti-static wrist strap for LED users, set a good anti-static grounding system, ion wind machines and other equipment.

The common form of LED connection circuit

1 Series: this circuit requires a higher voltage power supply.

V = each LED VF and =VF1+VF2+VF3+VF4------+VFN

I = single LED IF

2 parallel: this circuit requires a power supply can provide higher current.

V = single LED VF

I = each LED IF and =IF1+IF2+IF3+IF4------+IFN

3 Series / parallel combination

A, in practical use, the load is often used by the formation of series parallel array LED;

B, LED connected in series / parallel combination, can greatly reduce the impact due to a few LED VF caused by inconsistent;

C, LED array form or change the current limiting resistor should be changed accordingly.

Change d, serial / parallel combination will form the output current and input voltage with the ambient temperature and other factors are more significant;

4 in order to effectively control the current in the circuit, to configure the appropriate current limiting resistor in the circuit.

R= (V input voltage -VLED voltage /I (total) through the current limiting current resistance)

Limiting resistor's main function is to control the LED current, the voltage is more smooth, and the brightness of each parallel branch is more uniform. The limiting resistance effect is better, but the values of the current limiting resistor can not be too much, otherwise it will increase the power loss and component temperature can rise.

The classification and characteristics of power

1, the drive can be divided into two categories:

(1) constant flow: