LED drive power features and classification details
Published time: 2019-11-07
1. What is the LED driver?
The LED driving power source converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Usually, the input of the LED driving power source includes high-voltage power frequency AC (ie, mains), low-voltage DC, high-voltage DC, low-voltage high-frequency. AC (such as the output of an electronic transformer). The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes. The core components of the LED power supply include a switch controller, an inductor, a switching component (MOSfet), a feedback resistor, an input filter component, an output filter component, and the like. According to different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
2, LED drive power features
(1) High reliability
Especially like the driving power supply of LED street lamps, it is installed at high altitude, the maintenance is inconvenient, and the maintenance cost is also large.
(2) High efficiency
LED is an energy-saving product, and the efficiency of driving the power supply is high. It is very important to dissipate heat from the power supply installed in the fixture. The power source has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.
(3) High power factor
The power factor is the load requirement of the grid. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the power factor of a single power consumer with low power has little effect on the power grid, the amount of lighting used at night is large, and the similar load is too concentrated, which will cause serious pollution to the power grid. For 30 watts to 40 watts of LED driver power, it is said that in the near future, there may be certain indicators for power factors.
(4) Drive mode
There are two types of traffic: 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 all the LED faults do not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, which is the driving mode adopted by “Zhongke Huibao”. The LEDs operate in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and it is necessary to solve a certain LED failure without affecting the operation of other LEDs. These two forms coexist for a while. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
(5) Surge protection
The ability of LED to resist surge is relatively poor, especially the ability to resist reverse voltage. It is also important to strengthen protection in this area. Some LED lights are installed outdoors, such as LED street lights. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have a certain lack of surge protection, and as the power supply and lamps are frequently replaced, the LED drive power supply should have the ability to suppress the intrusion of surges and protect the LED from damage.
(6) Protection function
In addition to the conventional protection function, it is better 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 can be divided into two categories:
(1) Constant current type
a, the current output of the constant current drive circuit is constant, and the output DC voltage varies within a certain range according to the magnitude of the load resistance. The load resistance is small, the output voltage is low, and the load resistance is larger. The voltage will be higher.
b. The constant current circuit is not afraid of load short circuit, but it is forbidden to completely open the load.
c. The constant current drive circuit drives the LED, which is ideal, but relatively high in price.
d. Pay attention to the maximum withstand current and voltage value used, which limits the number of LEDs used.
(2) Voltage regulation
a. When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, and the output current changes as the load increases or decreases;
b. The voltage regulator circuit is not afraid of the load open circuit, but it is forbidden to completely short the load.
c. Drive the LED with a voltage-stabilized driving circuit, and each string needs to be added with a suitable resistor to make each string of LEDs display brightness average;
d. The brightness will be affected by the rectified voltage change.
4. For LED street lamp driving power supply Currently, the constant current source power supply on the market is divided into two types: the overall constant current and the constant current through the road.
Overall constant current and constant current
Advantages and disadvantages
1. The cost is relatively low.
2. Electromagnetic compatibility is easy to handle.
3. LED light source panels are easy to design and can be directly connected in parallel.
4. Overall efficiency can reach more than 90%
5. Wiring is easy, the light source board only needs 2 wires. 1. The consistency of the VF value of the LED is very high, otherwise the current will be unbalanced and thus damaged. 1. The VF consistency requirements for LEDs are not high, and the current is very average for each channel. LED work is more reliable.
1. The cost is relatively high.
2. Electromagnetic compatibility is not easy to handle.
3. Overall efficiency is not high up to 85%
4. Wiring is easy, the light source board only needs 2 wires.
It can also be seen from the above comparison that although the constant current is relatively high, the cost is 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 high stability constant current source power supply, specifically:
4.1 High stability, high power factor.
4.2 Long life, at least 5,000 hours or more.
4.3 Higher overall efficiency.
4.4 Superior environmental adaptability. Such as working environment temperature -20-60 degrees lightning strike 4KV and so on.
4.5 Waterproof rating should be above IP66.
To solve the above requirements, the following problems should be solved.
a. To meet high power factor and efficiency, LLC efficiency is relatively high, but not stable enough. Because it works by the leakage inductance of the transformer. The positive and synchronous synchronous rectification efficiency is also relatively high, but the current forward synchronous rectification technology is more complicated. Quasi-resonant plus synchronous rectification is relatively low in efficiency, but the stability is good and the scheme is mature. So choose quasi-resonant plus synchronous rectification.
b. Because the quasi-resonant plus synchronous rectification scheme can not be without electrolytic capacitors. Therefore, the design and component selection margin is relatively large, and the life expectancy is higher. At the same time, in order to meet the requirements of the working environment, the components used must be at least -20-105 degrees of temperature resistance.
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 glued to meet the IP protection level.
5, the status quo of LED power supply
LED power supply is also an accessory product. At present, the power quality of the market is uneven. According to the query of existing data and the problem of bad lights encountered in project execution, the reasons for the current shortage of LED driver power are analyzed.
a. The technical personnel of the company producing LED lighting and related products have insufficient understanding of the switching power supply, and the power supply can work normally, but some key evaluations and electromagnetic compatibility considerations are not enough, and there are certain hidden dangers.
b. Most LED power supply manufacturers are transforming from ordinary switching power supply to LED power supply. It is not enough to know the characteristics and use of LED.
c. At present, there are almost no standards for LEDs, most of which are based on the standards of switching power supplies and electronic rectifiers.
d. Most of the LED power supplies are not unified now, so most of them are relatively small. The purchase volume is small, the price is high, and the component suppliers are not very cooperative.
e, LED power supply stability: wide voltage input, high temperature and low temperature work, over temperature, over voltage protection and other issues are not resolved.
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