LED drive power basics!

1. What is the LED driver power supply?

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

LEDs are energy-saving products, and the efficiency of driving power supplies 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 grid's load requirements. 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 LEDs to withstand surges is relatively poor, especially against reverse voltage capability. 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, the power supply preferably increases 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. Classified by driving method

(1) Constant current type

The output current of the constant current driving circuit is constant, and the DC voltage of the output varies within a certain range according to the magnitude of the load resistance. The load resistance is small, the output voltage is low, the load resistance is larger, and the output voltage is also The higher;

The constant current circuit is not afraid of load short circuit, but it is forbidden to completely open the load;

The constant current drive circuit is ideal for driving LEDs, but it is relatively expensive; it should be noted that the maximum current and voltage values used limit the number of LEDs used.

(2) Voltage regulator

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;

The voltage regulator circuit is not afraid of the load open circuit, but it is forbidden to completely short the load;

Driving the LED with a voltage-stabilized driving circuit, each string needs to be added with a suitable resistor to make each string of LEDs display brightness average;

The brightness is affected by the rectified voltage changes.

4. Advantages and disadvantages of overall constant current and path-by-channel constant current operation

Compared with the overall constant current, the constant current is more disadvantageous and the cost is higher. But it can really protect the LED and extend the life of the LED, so the constant current is the future trend.

5, the shortage of LED power supply

LED driver power supply currently has insufficient reasons:

The technicians 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;

Most LED power supply manufacturers are transforming from ordinary switching power supply to LED power supply, and the characteristics and usage of LED are not enough;

At present, there are almost no standards for LEDs, and most of them are standards for reference switching power supplies and electronic rectifiers;

Most 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;

The stability of the LED power supply: wide voltage input, high temperature and low temperature operation, over temperature, over voltage protection and other issues are not solved one by one;

The first is the overall life of the driver circuit, especially the key components such as: the life of the capacitor at high temperatures directly affects the life of the power supply;

LED drivers should challenge higher conversion efficiency, especially when driving high-power LEDs, because all power that is not used as light output is dissipated as heat, and the power conversion efficiency is too low, which affects the energy-saving effect of LEDs. Play

At present, in the application of low power (1-5W), the proportion of constant current driving power supply has been close to 1/3, which is close to the cost of the light source, which has affected the market to some extent.