According to the rules of the electricity grid and the characteristics of the LED drive power requirements, the selection and design of LED drive power to take into account the performance characteristics of the nine requirements and try to optimize LED design.
1. What is the LED drive power
LED drive power to convert the power supply to a specific voltage and current to drive the LED light voltage converter, typically: LED drive power input including high frequency alternating current (ie electricity), low-voltage direct current, high voltage direct current, low-voltage high-frequency AC (such as electronic transformer output) and the like. The LED drive power output to be the most value with the LED forward voltage variations change in voltage constant current source. LED power supply core components include switching controller, inductor, switching components (MOSfet), the feedback resistor, the input filter components, the output of the filter element, and so on. Depending on the situation, we should also have input overvoltage protection, input under-voltage protection circuit, LED open circuit protection, overcurrent protection circuit.
2, LED drive power features
(1) High reliability
Especially as LED street lamp drive power, installed at high altitude, convenient maintenance, maintenance cost is also large.
(2) high efficiency
LED energy-saving products, power supply efficiency is higher. For the power junction cooling installation in the fixture is very important. High-efficiency power supply, its small power consumption, heat in the fixture is small, it reduces the temperature rise of the lamp. Advantageously LED light failure delaying.
(3) high power factor
Grid power factor load requirements. Usually 70 watts of electrical appliances, there is no mandatory targets. Although it is not a single low-power electrical power factor has little effect on the grid, but at night the use of a large amount of lighting, similar load is too concentrated, the grid will produce more serious pollution. For 30 watts to 40 watts of LED drive power, it is said in the near future, perhaps would have some power factor aspects of the indicator.
(4) Drive mode
Now prevailing in two ways: one is a constant source for multiple constant current source, constant current source for each channel individually to each LED power supply. In this way, the combination of flexible, all the way LED failure does not affect other LED's work, but the cost will be slightly higher. The other is a direct constant current power supply is "Branch Hui Bao" to change the drive mode used, LED in series or parallel operation. It has the advantage of low cost little, but flexibility is poor, but also to solve a LED failure does not affect other LED running issue. These two forms coexist for some time. Multi-channel constant current output power supply, in terms of cost and performance will be better. Perhaps the future direction of the mainstream.
(5) surge protection
LED anti-surge capacity is relatively poor, especially anti-reverse voltage capability. Strengthen the protection of this area is also important. Some LED lights installed in the outdoors, such as LED lights. Since the start grid load rejection, and lightning induction, from the grid system will invade a variety of surge, surge can cause some damage to the LED. Therefore Analysis "in Section Hui Bao" drive power surge protection should have a certain lack, as for the power supply and frequent replacement lamps, LED drive power surge suppression have invasive capacity LED is not damaged protection.
In addition to regular power protection features, the best increase in the constant current output LED temperature negative feedback to prevent LED overheating; To meet safety and electromagnetic compatibility requirements.
3, by driving classification
(1) constant current
Constant current drive circuit output is constant, while the output DC voltage but with the load resistance of different sizes vary within a certain range, the load resistance is small, the output voltage is low, the greater the load resistance, the output voltage higher;
Constant load short circuit is not afraid, but non-load completely open;
Drive LED constant current drive circuit is ideal, but the relatively high price;
It should be noted that to withstand the maximum current and voltage values to use, it limits the number of LED's use.
(2) Regulators formula
When the voltage regulator circuit parameters to determine the output voltage is fixed, and the current output has changed as the load increases or decreases;
Regulator circuit is not afraid of open load, but the load is completely non-short-circuit;
In regulator drive circuit drives LED, each string need only add an appropriate resistor so that each string of LED display brightness average;
Brightness will be affected by changes in the voltage from the rectifier.
4, the overall constant current and constant road works by the advantages and disadvantages
Compared with the overall constant current, constant current by road although more disadvantages, cost is relatively high. But it can really protect and extend the life of the LED LED, so by way of constant current is the future trend.