First, let's talk about what is LED driving power? It can convert the power supply into a specific voltage and current to drive the LED voltage converter. Generally, the input of LED driving power includes high-voltage power frequency AC (that is, mains power), low-voltage DC, high-voltage DC, low-voltage high-frequency AC (Such as the output of an electronic transformer). The output of the LED driving power is mostly a constant current source that can change the voltage as the forward voltage drop of the LED changes.
LED power supply core components include switching controllers, inductors, switching components (MOSfet), feedback resistors, input filter devices, output filter devices, and so on. 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.
Classification by driving method
(1) Constant current
The output current of the constant current drive circuit is constant, but the output DC voltage changes within a certain range with the size of the load resistance. The smaller the load resistance, the lower the output voltage, and the larger the load resistance, the higher the output voltage. The higher
Constant current circuit is not afraid of load short circuit, but it is strictly forbidden that the load is completely open circuit;
Constant current drive circuit is ideal for driving LED, but the price is relatively high;
Pay attention to the maximum current and voltage value used, which limits the number of LEDs used.
After the parameters of the voltage stabilization circuit are determined, the output voltage is fixed, but the output current changes with the increase and decrease of the load;
The voltage stabilization circuit is not afraid of the open circuit of the load, but it is strictly forbidden to completely short the load;
Drive the LEDs with a voltage-stabilized drive circuit. You need to add a suitable resistor for each string to make each string of LEDs display the average brightness;
Brightness is affected by voltage changes from rectification.
Characteristics of LED drive power
(1) High reliability
It is particularly like a driving power source for LED street lights, which is installed at a 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 should be high. It is important for the heat dissipation of the junction where the power supply is installed in the luminaire. The efficiency of the power supply is high, its power consumption is small, the heat generation in the lamp is small, and the temperature rise of the lamp is reduced. 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 are no mandatory indicators for household appliances below 70 watts. Although the power factor of a single consumer with a small power is lower, it has little effect on the power grid. However, at night, the amount of lighting is large, and similar loads are too concentrated, which will cause serious pollution to the power grid. For 30W to 40W LED drive power, it is said that in the near future, there may be certain index requirements for the power factor.
(4) Driving method
There are two kinds of traffic now: 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 LED failures along the way will 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". The LEDs run in series or in parallel. Its advantage is lower cost, but poor flexibility. It also needs to solve the problem of one LED failure, which does not affect the operation of other LEDs. These two forms coexist for a period of time. Multi-channel constant current output power supply method will be better in terms of cost and performance. Maybe the mainstream direction in the future.
(5) Surge protection
The anti-surge capability of LED is relatively poor, especially the anti-reverse voltage capability. It is also important to strengthen this protection. 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 LEDs. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have some shortcomings 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 function, it is best to add negative feedback of LED temperature to the constant current output to prevent the LED temperature from becoming too high; it must meet the requirements of safety regulations and electromagnetic compatibility.
The advantages and disadvantages of the overall constant current and road-by-channel constant current working methods
Compared with the overall constant current, although the constant current from one channel to another has more disadvantages, the cost is also higher. However, it can truly protect the LED and extend the life of the LED, so constant current is the future trend.