Knowledge summary of LED driving power

1, what is led drive power ?

LED drive power supply to convert the supply of power supplies to a specific voltage current to drive LED light-emitting voltage converter, usually: LED drive power input including high-voltage frequency exchange (ie, mains), Low-voltage DC, high-voltage DC, low-voltage high-frequency communication (such as the output of electronic transformers). And the output of LED drive power is mostly the constant current source which can change the voltage with the positive pressure drop value of the LED. LED power supply core components include switch controller, inductor, switch components (MOSFET), feedback resistors, input filter devices, output filter devices and so on.


According to the requirements of different occasions, but also have input overvoltage protection circuit, input undervoltage protection circuit, led open circuit protection, over-current protection and other circuits.

  

2, the characteristics of LED driving power


(1) High reliability


Especially like LED street lamp driving power, installed in high altitude, maintenance inconvenient, maintenance costs are also large.


(2) High efficiency LED is energy-saving products, the efficiency of driving power is high. It is very important for the power supply to be installed in the lamp in the junction cooling. The efficiency of the power supply is high, its power consumption is small, the heat in the lamp is small, and the temperature rise of the lamp is lowered.


It's good for slowing down the LED's light decay.


(3) High power factor Power factor is the requirement of power grid to load. General 70 Watts below the electric device, there is no mandatory indicator. Although the power of a small number of electrical power is not very small impact on the power grid, but the use of lighting at night, the same kind of load too concentrated, the network will produce more serious pollution.


For the 30 Watts ~40 Watt LED drive power, it is said that in the near future, may have a certain index requirements for power factors.


(4) Drive mode There are two kinds of current: one is a constant pressure source for a number of constant current source, each constant current source alone to each led power supply. This way, the combination of flexible, LED fault, does not affect the work of other LEDs, but the cost will be slightly higher. The other is the direct constant current power supply is the "Zhong Ke hui Bao" modified by the driving mode, LED series or parallel operation. Its advantages are low cost, but the flexibility is poor, but also to solve an LED fault, does not affect other led operation problems. These two forms coexist in a period of time. Multi-channel constant current output power supply mode, in terms of cost and performance will be better.


Maybe it's the next major direction.


(5) Surge protection LED surge resistance 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 streetlights. Due to the power grid load and lightning induction, from the grid system will invade a variety of surges, some surges will lead to damage to the LED.


Therefore, the analysis of "Zhong Ke hui bao" drive power in the surge protection should have a certain lack, and as for the power and lamps frequent replacement, LED drive power supply to inhibit surge intrusion, protect the LED is not damaged ability.


(6) Protection function In addition to the normal protection function, it is best to increase the LED temperature negative feedback in constant current output to prevent the LED temperature from being too high; to meet the requirements of safety and electromagnetic compatibility.


  

  

3, by the driving mode classification


(1) constant-current


Constant current drive circuit output is constant, and the output of DC voltage with the load resistance of different sizes within a certain range of changes in the load resistance is small, output voltage is low, the higher the load resistance, the higher the output voltage;


Constant current circuit is not afraid of load short circuit, but strictly prohibit the load completely open;


The constant current drive circuit drives the LED is ideal, but relatively high price;


Attention should be paid to the maximum withstand current and voltage value, which limits the number of LEDs used.


(2) Regulated type


When the parameters of the voltage stabilizing circuit are determined, the output voltage is fixed, and the output current is changed with the increase and decrease of the load.


Voltage regulator Circuit is not afraid of the load open, but strictly prohibited load short circuit;


To stabilize the driving circuit to drive the LED, each string needs to be coupled with the appropriate resistor to make each LED display brightness average;


The brightness is affected by the voltage changes that are rectified.


4. The advantages and disadvantages of the whole constant current and the way constant current working method Compared with the whole constant current phase, the Lu Henglui is more difficult and the cost is higher.


But it can really play to protect the LED and prolong the life of the LED, so the constant flow by road is the future trend.


5, the lack of LED power supply


LED Drive power supply there is a shortage of reasons:


The production of LED lighting and related products of the company's technical personnel on the switching power supply is not enough to make a power supply can be normal work, but some critical assessment and electromagnetic compatibility is not enough, or have a certain hidden trouble;


Most of the LED power production enterprises from the ordinary switching power supply to do the LED power supply, the characteristics of the LED and the use of knowledge is not enough;


At present, there are few standards about LEDs, most of them are reference switching power supply and electronic rectifier standards; Now most of the LED power supply is not unified, so most of the volume is relatively small.


The purchase quantity is small, the price is high, moreover the component supplier also does not cooperate very much;


LED power supply Stability: wide voltage input, high temperature and low temperature work, over temperature, over-voltage protection problems are not one by one to solve;


First, the whole life of the driving circuit, especially the key devices such as: capacitance at high temperature directly affect the life of the power supply;


Is the LED driver should challenge a higher conversion efficiency, especially in the drive high-power led when more so, because all the power is not as the output of light as heat dissipation, power conversion efficiency is too low, the impact of the LED energy-saving effect of the play; At present, in the application of Small power (1-5w), the proportion of constant current drive power supply is nearly 1/3, which has been close to the cost of light source, and has influenced the market promotion to some extent.