What is LED driver power?
1.The LED driver power supply converts the power supply into a specific voltage and current to driver the LED light-emitting voltage converter. Generally, the input of the LED driver power supply includes high-voltage power frequency AC (that is, commercial power), low-voltage DC, high-voltage DC, low-voltage high-frequency AC (such as the output of an electronic transformer), etc. The output of the LED driver power supply is mostly a constant current source that can change the voltage with the change of the LED forward voltage drop value. The core components of LED power supply include switching controller, inductor, switching component (MOSfet), feedback resistor, input filter device, output filter device, etc. According to the requirements of different occasions, there must be input over-voltage protection circuit, input under-voltage protection circuit, LED open circuit protection, over-current protection and other circuits.
2. Characteristics of LED driver power
(1) High reliability Especially like the driving power of LED street lamp, it is installed at high altitude, which is inconvenient for maintenance and the cost of maintenance is also large.
(2) High-efficiency LEDs are energy-saving products, and the efficiency of the driving power supply is high. It is very important for the heat dissipation of the power supply installed in the lamp. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is good for delaying the decay of LED.
(3) High power factor The power factor is the load requirement of the power grid. Generally, there is no mandatory index for electrical appliances under 70 watts. Although the power factor of a single consumer with low power is a little low, it has little effect on the power grid, but the amount of lighting used at night is large, and the similar loads are too concentrated, which will cause serious pollution to the power grid. For the LED driver power of 30 watts ~ 40 watts, it is said that in the near future, there may be certain index requirements for power factors.
(4) driver mode There are two types of traffic: one is a constant voltage source for multiple constant current sources, and each constant current source separately supplies power to each LED. In this way, the combination is flexible, all the way LED failure, does not affect the work of other LEDs, but the cost will be slightly higher. The other is the direct constant current power supply, which is the driving method adopted by Zhongke Huibao, where LEDs are operated in series or in parallel. Its advantage is that the cost is a bit lower, but the flexibility is poor, and it is necessary to solve the problem of a certain LED and not affect the operation of other LEDs. These two forms coexist for a period of time. The muti-channel constant current output power supply method will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
(5) Surge protection LED's ability to resist surge is relatively poor, especially the ability to resist reverse voltage. 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-off of the grid load and the induction of lightning strikes, various surges will invade from the grid system, and some surges will cause damage to the LED. Therefore, the analysis of the "Zhongke Huibao" driver power supply should have some deficiencies in surge protection. As for the frequent replacement of power supplies and lamps, the LED driver power supply must have the ability to suppress the intrusion of the surge and protect the LED from damage.
(6) Protection function In addition to the conventional protection function, it is best to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it must meet the requirements of safety regulations and electromagnetic compatibility.
3. According to the driving method, it can be divided into two categories:
(1) Constant current type:
a. The current output by the constant current driver circuit is constant, but the output DC voltage varies within a certain range with the size of the load resistance. The load resistance is small, the output voltage is low, and the load resistance is larger The higher the voltage.
b. The constant current circuit is not afraid of short circuit of the load, but it is strictly forbidden to completely open the load.
c. The constant current driver circuit is ideal for driving LEDs, but relatively expensive.
d. It should be noted that the maximum withstand current and voltage value used, which limits the number of LEDs used.
(2) Voltage regulator type:
a. When the parameters in the voltage regulator circuit are determined, the output voltage is fixed, and the output current changes with the increase and decrease of the load;
b. The voltage-stabilizing circuit is not afraid of open circuit of the load, but it is strictly forbidden to completely short-circuit the load.
c. The LED is driven by a voltage-stabilized driving circuit, and each string needs to be added with an appropriate resistance to make each string of LED display brightness average;
d. The brightness will be affected by the voltage change from the rectification.
4. For LED street lamp driving power supply, the current constant current source power supply on the market is divided into: overall constant current and channel-by-channel constant current. These two working methods have their own advantages and disadvantages:
Overall constant current
Advantages and disadvantages
1. The cost is relatively low.
2. Electromagnetic compatibility is easy to handle.
3. LED light source board is easy to design and can be directly connected in parallel.
4. The overall efficiency can reach more than 90%
5. Wiring is easy, the light source board only needs 2 wires.
1. The consistency of VF value of LED is very high, otherwise it will cause current imbalance and damage.
2. The VF consistency of the LED is not high, and each current is very average. LED work is more reliable.
3. The cost is relatively high.
4. Electromagnetic compatibility is not easy to handle.
5. The overall efficiency is not high up to 85%
6. Wiring is easy, the light source board only needs 2 wires.
From the above comparison, it can also be seen that although the channel-by-channel constant current has many disadvantages, the cost is also relatively high. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.
To achieve a higher stability of the constant current source power supply, specifically:
1 High stability and high power factor.
2 Long life, at least 5000 hours.
3 Higher overall efficiency.
4 Super environmental adaptability. Such as working environment temperature -20-60 degrees lightning strike 4KV and so on.
5 The waterproof rating must be above IP66.
For the above requirements, the following problems should be solved.
a. To meet high power factor and efficiency, LLC efficiency is relatively high, but it is not stable enough. Because it works by the leakage inductance resonance of the transformer. The efficiency of forward synchronous rectification is also relatively high, but the current technology of forward synchronous rectification is relatively complicated. Compared with the above two, quasi-resonance and synchronous rectification have slightly lower efficiency, but good stability and mature solutions. So choose quasi-resonant plus synchronous rectification.
b. Because the scheme of quasi-resonance plus synchronous rectification cannot be without electrolytic capacitors. Therefore, electrolytic capacitors with a relatively large margin in design and component selection and a long life are selected. At the same time
, in order to meet the requirements of the working environment, the components used must be at least -20-105 degrees temperature resistant.
c. In order to meet the requirements of electromagnetic compatibility and lightning strike at the input end, it is necessary to add lightning protection circuit and EMC filter circuit. Some high-frequency places still need to be shielded.
d. The power supply is filled with glue to meet the requirements of IP protection.
5. Status of LED power supply
LED power supply is also a supporting product. At present, the quality of power supply in the market is uneven. According to the query of existing data and the problem of bad lights encountered in the implementation of the project, the reasons for the current shortage of LED driver power are roughly analyzed:
a. The technical personnel of the company producing LED lighting and related products do not have enough understanding of the switching power supply, and the power supply made can work normally, but some key evaluations and electromagnetic compatibility considerations are not enough, and there are still certain hidden dangers.
b. Most LED power supply manufacturing enterprises are converted from ordinary switching power supplies to make LED power supplies, and their understanding of the characteristics and use of LEDs is not enough.
c. At present, there are almost no standards for LEDs. Most of them refer to the standards of switching power supplies and electronic rectifiers.
d. Most LED power supplies are not unified now, so most of them are relatively small. Small purchases result in high prices, and component suppliers are not very cooperative.
e. Stability of LED power supply: wide voltage input, high and low temperature operation, over temperature, over voltage protection and other issues have not been solved one by one.