LED Lighting Knowledge: LED Driver Power Supply

1,What is an LED driver power supply?

1.The LED driving power supply converts the power supply into a specific voltage and current to drive the LED light-emitting voltage converter. Normally: the input of the LED driving power supply includes high-voltage industrial frequency AC (ie, mains power), low-voltage DC, high-voltage DC, and low-voltage high frequency. AC (such as the output of an electronic transformer), etc. The output of the LED driving power supply is mostly a constant current source that changes the voltage as the LED forward voltage drop value changes.

2.The core components of LED power supply include switching controllers, inductors, switching components (MOSfet), feedback resistors, input filter components, output filter components, etc. According to the requirements of different occasions, there are also input overvoltage protection circuits, input undervoltage protection circuits, LED open circuit protection, overcurrent protection and other circuits.

2, Characteristics of LED driver power supply

1.High reliability. Especially like the driving power supply of LED street lights, it is installed at high altitude, making maintenance inconvenient and expensive.

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 from the junction where the power supply is installed inside the luminaire. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which also reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LED.

3.High power factor. Power factor is the requirement of the power grid for the load. Generally, there are no mandatory indicators for electrical appliances below 70 watts. Although the low power factor of a single electrical appliance with small power will have 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. For 30- to 40-watt LED driving power supplies, it is said that there may be certain index requirements for power factors in the near future.

Beon project: Foshan Metro Line No.1-No.3, Which offered all flood lights with beon drivers

4.Driving methods.  There are currently two popular methods: one is Constant Voltage LED Driver that supplies multiple constant current sources, and each constant current source supplies power to each LED independently. In this way, the combination is flexible. If one LED fails, it will not affect the work of other LEDs, but the cost will be slightly higher. The other is Constant Current LED Driver, with LEDs running in series or parallel. Its advantage is that the cost is lower, but the flexibility is poor. It also needs to solve the problem of a certain LED failure without affecting the operation of other LEDs. These two forms coexisted for some time. The Constant Current LED Driver will be better in terms of cost and performance. Maybe it will be the mainstream direction in the future.

5.Surge protection. LED’s ability to withstand surges is relatively poor, especially its ability to withstand reverse voltage. Strengthening protection in this area is also important. Some LED lights are installed outdoors, such as LED street lights. Due to the switching of the power grid load and the induction of lightning strikes, various surges will invade from the power grid system, and some surges will cause damage to the LED. Therefore, All of our BEON LED driver have certain deficiencies in surge protection. As for the frequent replacement of power supplies and lamps, the LED driving power supply must have the ability to suppress the intrusion of surges and protect the LED from damage.

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

3, It can be divided into two categories according to the driving method.

(1)  Constant current LED Driver:

a. The current output by the constant current drive circuit is constant, but the output DC voltage changes within a certain range with the load resistance. The smaller the load resistance, the lower the output voltage. The larger the load resistance, the lower the output voltage. The voltage will be higher.

b. The constant current circuit is not afraid of the load being short-circuited, but the load is strictly prohibited from being completely open-circuited.

c. Constant current driving circuit is ideal for driving LED, but it is relatively expensive.

d. Pay attention to the maximum current and voltage values used, which limits the number of LEDs used.

(2) Constant voltage LED Driver:

a. When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, but the output current changes with the increase or decrease of the load;

b. The voltage stabilizing circuit is not afraid of the load opening, but it is strictly forbidden for the load to be completely short-circuited.

c. Use a voltage-stabilizing drive circuit to drive LEDs, and each string needs to add a suitable resistor to make each string of LEDs display even brightness;

d. The brightness will be affected by the voltage change from rectification.

4, Current status of LED driver power supply

LED power supply is also a supporting product. The quality of power supply currently on the market is uneven. Based on the inquiry of existing data and the problem of bad lights encountered during project execution, the reasons for the current shortcomings of LED driving power supply are roughly analyzed:

a. The technical staff of companies that produce LED lighting and related products do not know enough about switching power supplies. The power supplies they make can work normally, but some key evaluations and electromagnetic compatibility are not considered enough, and there are still certain hidden dangers.

b. Most LED power supply manufacturers have transformed from ordinary switching power supplies to LED power supplies, and do not have enough understanding of the characteristics and uses of LEDs.

c. There are currently almost no standards for LEDs, and most of them refer to the standards of switching power supplies and electronic rectifiers.

d. Nowadays, most LED power supplies are not unified, so the quantities are mostly relatively small. The purchase quantity is small, the price is high, and the component suppliers are not very cooperative.

e. Stability of LED power supply: wide voltage input, high and low temperature operation, over-temperature, over-voltage protection and other issues have not been solved one by one.

f. First, the overall life of the drive circuit, especially the life of key components such as capacitors at high temperatures, directly affects the life of the power supply.

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

h. Currently, in applications with smaller power (1-5W), the cost of constant current drive power supplies accounts for close to 1/3, which is close to the cost of light sources, which affects market promotion to a certain extent.

5, How to choose high-quality LED driver power supply

5.1 According to the characteristics of LED, please pay attention to the following when selecting the driving power supply:

a. According to the LED current and voltage characteristics, it is ideal to use constant current drive. It can avoid current changes caused by changes in the LED forward voltage, and at the same time, the constant current stabilizes the brightness of the LED.

b. In addition, LED luminous flux is inversely proportional to temperature, so power supply heating should be minimized and a well-designed heat dissipation system should be used. Thereby reducing the working temperature of the LED.

c. In order to ensure the overall life of the LED, the temperature of the LED must be controlled within a certain range.

5.2 According to the power consumption characteristics of the power grid, the requirements of LED characteristics and related LED products, the following points should be considered when selecting LED driving power supply:

a. High reliability

LED products mainly consist of LED chips and power supplies, heat dissipation casings, control circuits, etc. The quality of the LED power supply directly affects the quality of the product. Especially LED street light products, because they are installed at high altitudes, maintenance is inconvenient and costly.

b. High efficiency

LED is an energy-saving product, and the driving power supply must also meet energy-saving requirements. Especially the structure where the power supply is installed inside the lamp is particularly important.

Because the luminous efficiency of LED decreases as the LED temperature increases. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which also reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LED.

c. Constant current drive mode

In order to match the VI characteristics of LED, the LED power supply must use constant current drive.

d. Surge protection

LEDs have poor impact resistance, so protection in this area must be strengthened. Especially for some products installed outdoors, due to the start-up and lightning of the grid load. Therefore, the LED driving power supply must have the ability to suppress surge intrusion and protect the LED from damage.

e. Temperature protection function

In addition to the conventional protection functions of the power supply, it is best to add LED chip temperature negative feedback in the constant current output to prevent the LED chip PN junction temperature from being too high.

f. LED power supply life

The life of the driving power supply is matched with the life of the LED chip as much as possible.

g. Working environment issues

Because the environment in each place is different, it is important to consider the environment of the workplace where LED lamps are used, such as: temperature, humidity, installation location, etc.