Detailed explanation of the three most popular LED

Details of three commonly used LED driving power supplies

LED driving power supply is a power converter that converts the power supply into a specific voltage and current to drive the led to emit light. Generally, the input of LED driving power supply includes high-voltage power frequency AC (i.e. mains power), low-voltage DC, high-voltage DC, low-voltage high-frequency AC (such as the output of electronic transformer), etc

the output of LED driving power supply is mostly a constant current source that can change the voltage with the change of led forward voltage drop value

characteristics of LED driving power supply

1 High reliability, especially the driving power supply of LED street lights, installed at high altitude, with waterproof aluminum shell driving power supply, it is not easy to break if the quality is good, and the number of maintenance is reduced

2. High efficiency LED is an energy-saving product, and the efficiency of driving power supply should be high. It is particularly important for the structure where the power supply is installed in the lamp. Because the luminous efficiency of LED decreases with the increase of LED temperature, the heat dissipation of LED is very important. The efficiency of the power supply is high, its power consumption is small, and the calorific value in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light failure of LED

3. High power factor power factor is the requirement of electricity for load. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of a single electric appliance with small power is a little lower, it has little impact on electricity, but when everyone lights up at night, the load of the same kind is too concentrated, which will cause serious pollution to electricity. For 30-40 watt LED drive power supply, it is said that in the near future, there may be certain index requirements for power factor

4. At present, there are two driving modes: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. In this way, the combination is flexible, and the failure of one LED will not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, LED series or parallel operation. Its advantage is that the cost is a little low, but the flexibility is poor. It also needs to solve the problem that the failure of one LED does not affect the operation of other LEDs. These two forms coexist for a period of time. The multi-channel constant current output power supply mode will be better in cost and performance. It may be the mainstream direction in the future

5. The anti surge ability of surge protection LED is relatively poor, especially the anti reverse voltage ability. It is also important to strengthen protection in this regard. Some LED lights are installed outdoors, such as LED street lights. Due to the start and fall of electrical load and the induction of lightning stroke, various surges will invade the slave electrical system, and some surges will cause led damage. Therefore, the LED driving power supply should have the ability to suppress the invasion of surge and protect the LED from damage

6. Protection function in addition to the conventional protection function, it is best to add LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high

7. In terms of protection, the lamps should be installed outside, the power structure should be waterproof and moisture-proof, and the shell should be sun resistant

8. The service life of the driving power supply should match the service life of the LED

9 Meet the requirements of safety regulations and electromagnetic compatibility

shortage of LED driving power supply

reasons for the current shortage of LED driving power supply:

(1) the production of LED lighting and related technicians do not know enough about switching power supply, and the power supply made can work normally, but some key evaluations and electromagnetic compatibility considerations are not enough, there are still certain hidden dangers

(2) most LED power supply production is transformed from ordinary switching power supply to LED power supply, and there is insufficient understanding of the characteristics and use of LED

(3) there are almost no standards for LED, most of which refer to the standards of switching power supply and electronic rectifier

(4) at present, most LED power supplies are not unified, so most of them are relatively small. The purchase volume is small, the price is high, and the component suppliers are not very cooperative

(5) stability of LED power supply: wide voltage input, high and low temperature operation, over temperature, over voltage protection and other problems have not been solved one by one

development direction of LED driving power supply

1. Improve the service life of driving power supply

led has one of the very important advantages: long service life, about 30000-100000 hours. The traditional LED driving power supply contains electrolytic capacitors, and the service life of electrolytic capacitors is relatively short, about 5000 hours, which is the main reason for restricting the service life of LED driving power supply. Therefore, electrolytic capacitors should not be used in LED driving power supply as far as possible

it is worth mentioning that

2. Improve the input power factor of the driving power supply and reduce the total harmonic distortion. The "EnergyStar" solid-state lighting document issued by the U.S. Department of energy stipulates that power factor correction is mandatory for any power level. This standard is applicable to a series of products, such as table lamps, cabinet lamps, etc. Among them, the power factor of LED driving power supply for household lighting must be greater than 0.7, and that for commercial lighting must be greater than 0.9. IEC harmonic content standard stipulates that in lighting with power level greater than 25W, total harmonic distortion (THD) shall be less than 35%, and power factor shall not be less than 0.7. The introduction of these standards puts forward higher requirements for the design of LED lighting driving power supply

3. Reduce the volume of the driving power supply

led itself is relatively small, which is very beneficial to portable products. The driving power supply of LED should also be as small as possible, so that it can be smoothly installed into the LED lamp holder. In the design process, the volume of the driving power supply should be minimized

4. Improve the reliability of the driving power supply

in the process of LED operation, non-human factors such as high temperature and aging devices will cause fatal damage to the LED body. Therefore, over-voltage protection, over-current protection and other protection circuits should be added to the LED driving power supply to deal with emergencies and ensure the safe work of the LED body

detailed explanation of three commonly used LED driving power supplies

at present

1, switching constant current source

adopts transformer to change high voltage into low voltage, and carries out rectification and filtering, so as to output stable low-voltage DC. Switching constant current source is divided into isolated power supply and non isolated power supply. Isolation refers to the isolation of high and low output voltage, which has very high safety, so the requirements for shell insulation are not high. The non isolated safety is slightly poor, but the cost is relatively low. The traditional energy-saving lamp is separated from the power supply through the experiment, and protected by an insulating plastic shell. Switching power supply has relatively high safety (generally low output voltage) and stable performance. Its disadvantages are complex circuit and high price. With mature technology and stable performance, switching power supply is the mainstream power supply of LED lighting at present

2. Linear IC power supply

one or more ICs are used to distribute the voltage. There are few types of electronic components, and the power factor and power efficiency are very high. Electrolytic capacitors are not required, so the service life is long and the cost is low. The disadvantage is that the output high voltage is not isolated, and there is stroboscopic, so the shell is required to do a good job of anti electric shock isolation protection. On the market, it is claimed that Linear IC power supply is adopted for those without (without) electrolytic capacitors and with ultra long service life. IC drive power supply has the advantages of high reliability, high efficiency and low cost, and is the ideal LED drive power supply in the future

3. The resistance capacitance step-down power supply

uses a capacitor to provide the driving current through its charge and discharge. The circuit is simple, the cost is low, but the performance is poor, and the stability is poor. When the electric voltage fluctuates, it is easy to burn out the LED. At the same time, the output high voltage is not isolated, and the insulating protective shell is required. With low power factor and short service life, it is generally only suitable for economical low-power products (within 5W)

products with high power have large output current, and the capacitor cannot provide large current, otherwise it is easy to burn out. In addition, the state has requirements for the power factor of high-power lamps, that is, the power factor above 7W is required to be greater than 0.7, but the resistance capacitance step-down power supply is far from reaching (generally between 0..3), so the resistance capacitance step-down power supply should not be used for high-power products. In the market, almost all low-end products with low requirements use resistance capacitance step-down power supply. In addition, some low-end products with high power also use resistance capacitance step-down power supply

cost performance comparison of several power supplies

taking 3W small bulb and 16W fluorescent tube as examples, the cost comparison of various power supplies:

it can be seen that the cost difference of different types of power supplies is very large, among which the certified switch isolation source is the most expensive, and the resistance capacitance step-down power supply is the cheapest

comparison of the performance of various power supplies:

in the medium and high-end market, the switching constant current power supply is still the mainstream power supply in the market, and manufacturers generally carry out high-voltage isolation in the structural design. In the low-end market, most manufacturers use resistance capacitance step-down power supply, and some manufacturers use linear IC power supply (manufacturers are required to have certain design ability)

with different power supplies, the performance and price of products are different. We should choose different products according to different markets