LED drive power is a voltage converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Generally, the input of the LED drive power 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 electronic transformers), etc. The output of the LED drive power supply is mostly a constant current source that can change the voltage as the LED forward voltage drop changes. The following provides some knowledge about LED drive power for those who are new to the industry.
1. What is LED drive power
The LED drive power supply converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Generally, the input of the LED drive 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 drive power supply is mostly a constant current source that can change the voltage as the LED forward voltage drop changes. The core components of the LED power supply include switching controllers, inductors, switching components (MOSfet), feedback resistors, input filter components, output filter components, etc. According to the requirements of different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
2. Characteristics of LED drive power
(1) High reliability
Especially like the driving power supply of LED street lamps, it is installed at high altitude, which is inconvenient for maintenance and the cost of maintenance is also large.
(2) High efficiency
LED is an energy-saving product, 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 beneficial to delay the light 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 LED drive power of 30 watts to 40 watts, it is said that in the near future, there may be certain index requirements for power factors.
(4) Drive method
There are currently 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 individually. 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, that is, "Zhongke Huibao" changed to the driving mode, LED series or parallel operation. 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 multi-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
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 regard. Some LED lights are installed outdoors, such as LED street lights. Due to the induction of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause damage to the LED. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have some deficiencies in terms of surge protection. As for the frequent replacement of power supplies and lamps, the LED drive 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 functions of the power supply, 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. Classification by driving method
(1) Constant current type
The current output by the constant current drive 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 larger the load resistance, the output voltage is The higher
The constant current circuit is not afraid of short circuit of the load, but it is strictly forbidden to completely open the load;
Constant current drive circuit is ideal for driving LED, but relatively high price;
It should be noted that the maximum withstand current and voltage values ​​used, which limits the number of LEDs used.
(2) Voltage regulator
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;
The voltage-stabilizing circuit is not afraid of open circuit of the load, but it is strictly forbidden to completely short-circuit the load;
The LED is driven by a voltage-regulated driving circuit, and each string needs to be added with an appropriate resistance to make each string of LED display brightness average;
The brightness will be affected by the voltage change from the rectification.
4. The advantages and disadvantages of the overall constant current and channel-by-channel constant current working methods
Compared with the overall constant current, the channel-by-channel constant current has more disadvantages and higher cost. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.
5. Insufficient LED power supply
Reasons for the shortage of LED drive power:
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;
Most LED power supply manufacturers 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;
At present, there are almost no standards for LEDs, most of which refer to the standards of switching power supplies and electronic rectifiers;
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;
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;
The first is the overall life of the drive circuit, especially the key components such as: the life of the capacitor at high temperature directly affects the life of the power supply;
LED drivers should challenge higher conversion efficiency, especially when driving high-power LEDs, because all the power that is not used as light output is dissipated as heat, and the power conversion efficiency is too low, which affects the LED energy-saving effect. Play
At present, in the applications with low power (1-5W), the proportion of the cost of constant current drive power supply is close to 1/3, which is close to the cost of the light source, which has affected the market promotion to a certain extent.
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