LED lighting LED driver power supply technology analysis

The key to the design of a good LED lighting product lies in heat dissipation, driving power supply, and light source. Heat dissipation is particularly important. The heat dissipation effect directly affects the life quality of the lighting product. The life of the driving power supply itself and the stability of the output current and voltage also have a great impact on the overall life quality of the product. The light source is the core part of the entire product.

LED driver power supply is also a supporting product. The quality of power supplies on the market is uneven. Here is some relevant knowledge about LED driver power supply.

1. What is LED driver power supply?

LED driver power is a voltage converter that converts power supply into a specific voltage and current to drive the LED to emit light. Under normal circumstances: the input of LED driver power includes high-voltage industrial frequency AC (i.e., mains), low-voltage DC, high-voltage DC, low-voltage high-frequency AC (such as the output of an electronic transformer), etc. The output of LED driver power is mostly a constant current source that can change the voltage as the forward voltage drop of the LED changes. The core components of LED power supply include switch controller, inductor, switch components (MOSfet), feedback resistor, input filter device, output filter device, etc. According to the requirements of different occasions, there are also input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.

2. Characteristics of LED driver power supply

(1) High reliability: Especially for LED street lamp drivers, which are installed at high altitudes, maintenance is inconvenient and the cost of maintenance is high.

(2) High-efficiency LED is an energy-saving product, and the efficiency of the driving power supply must be high. It is very important to dissipate heat when the power supply is installed in the lamp. The higher the efficiency of the power supply, the less power it consumes, and the less heat it generates in the lamp, which reduces the temperature rise of the lamp. This is beneficial to delaying the light decay of the 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 below 70 watts. Although a low power factor of a single low-power electrical appliance has little impact on the power grid, the large amount of lighting used at night and the concentration of similar loads will cause serious pollution to the power grid. It is said that there may be certain index requirements for power factor for 30-40 watt LED driver power supplies in the near future.

(4) Drive mode

There are two common methods now: one is to use a constant voltage source to supply multiple constant current sources, and each constant current source supplies power to each LED separately. This method has flexible combination, and the failure of one LED does not affect the operation of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, which is the driving method adopted by "Zhongke Huibao", and the LEDs are connected in series or in parallel. Its advantage is that the cost is lower, but the flexibility is poor, and the problem of a certain LED failure not affecting the operation of other LEDs must be solved. These two forms coexisted 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 will be the mainstream direction in the future.

(5) Surge protection

LEDs are relatively poor at resisting surges, especially 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 start-up of the grid load and the induction of lightning strikes, various surges will invade from the grid system, and some surges will cause damage to the LEDs. Therefore, it is analyzed that the driver power supply of "Zhongke Huibao" should have certain deficiencies in surge protection. As for the frequent replacement of power supplies and lamps, the LED driver power supply must have the ability to suppress the intrusion of surges and protect the LEDs from damage.

(6) Protection function

In addition to the conventional protection functions of the power supply, it is best to add LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it must comply with safety regulations and electromagnetic compatibility requirements.

3. Classification by driving mode

(1) Constant current type The output current of the constant current drive circuit is constant, while the output DC voltage varies 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 constant current circuit is not afraid of load short circuit, but it is strictly forbidden to completely open the load. The constant current drive circuit is ideal for driving LEDs, but the price is relatively high. Attention should be paid to the maximum current and voltage used, which limits the number of LEDs used.

(2) Voltage stabilization type: After the various parameters in the voltage stabilization circuit are determined, the output voltage is fixed, while the output current changes with the increase or decrease of the load; the voltage stabilization circuit is not afraid of open circuit load, but it is strictly forbidden to have a complete short circuit of the load; when driving the LED with a voltage stabilization drive circuit, each string needs to be added with a suitable resistor so that the brightness of each string of LEDs can be even; the brightness will be affected by the voltage change from the rectification.

4. Advantages and disadvantages of overall constant current and channel-by-channel constant current working modes

Compared with the overall constant current, although the channel-by-channel constant current has more disadvantages and higher cost, it can truly protect the LED and extend the life of the LED, so the channel-by-channel constant current is the future trend.

5. Insufficient LED power supply

The technical staff of the company producing LED lighting and related products do not have enough understanding of switching power supplies. The power supplies they make 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 have transformed from ordinary switching power supplies to LED power supplies, and they do not have enough understanding of the characteristics and use of LEDs; there are almost no standards for LEDs at present, and most of them refer to the standards of switching power supplies and electronic rectifiers; most LED power supplies are not unified, so the quantity is relatively small. The purchase volume is small, the price is high, and the component suppliers are not very cooperative; the stability of LED power supplies: wide voltage input, high and low temperature operation, over-temperature, over-voltage protection and other problems have not been solved one by one.

The first is the overall life of the drive circuit, especially the life of key components such as capacitors at high temperatures, which directly affects the life of the power supply; the second is that the LED driver should challenge higher conversion efficiency, especially when driving high-power LEDs, because all power that is not output as light is dissipated as heat, and the low power conversion efficiency affects the energy-saving effect of the LED; currently in applications with lower power (1-5W), the proportion of the constant current drive power cost is close to 1/3, which is close to the cost of the light source, affecting market promotion to a certain extent.