Learn more about LED drivers

LED driver power supply structure

1. What is LED driver power supply?


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. 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 altitudes, 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 essential to dissipate heat from the junction where the power supply is installed inside the luminaire. The power supply's efficiency 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 for delaying the decay of LED lights.


(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 soon.

(4) Driving method

There are two popular ones now: one is a constant voltage source that supplies multiple constant current sources, and each 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 a direct constant current power supply driving method, 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 multi-channel constant current output power supply method will improve 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 the power grid system, and some surges will cause damage to the LED.

(6) Protection function

In addition to the conventional protection functions of the 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. Classification by driver mode


(1) Constant current type

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. If the load resistance is small, the output voltage will be low. The larger the load resistance, the output voltage will be lower. the higher;

Constant current circuits are not afraid of load short-circuit, but the load is strictly prohibited from being completely open-circuited;

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

It should be noted that the maximum current and voltage values used limit the number of LEDs used.

(2) Stabilized voltage

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;

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

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

The brightness will be affected by the rectified voltage change.

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


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

5. Inadequacy of LED power supply


Reasons why LED driver power supplies are defective：

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 considerations are not enough, and there are still certain hidden dangers;

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

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

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

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;

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;

It is the LED driver that 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. to exert; to exert;

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.


Two major categories of LED drive power supplies

The LED driving power supply is a voltage converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Normally: the input of the LED driving power supply includes high-voltage power frequency AC (ie, mains power), low-voltage DC, high-voltage DC, low-voltage high-voltage 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.

Since the performance and conversion efficiency of various LED power supplies with different specifications are different, choosing a suitable and efficient LED dedicated power supply can truly reveal the high-efficiency characteristics of LED light sources. Because the low-efficiency LED power supply itself consumes a large amount of power, the energy-saving characteristics of LED cannot be highlighted in the process of powering the LED. In short, LED power supply plays an important role in the stability, energy saving and lifespan of LED operation.