Deep interpretation of OFweek: LED constant current drive and constant current IC inventory

LED constant current drive introduction


Since the LED is a characteristic sensitive semiconductor device and has a negative temperature characteristic, it needs to be stably operated and protected during the application process, thereby generating a driving concept. LED devices have almost strict requirements for driving power. Unlike ordinary incandescent bulbs, LEDs can be directly connected to 220V AC mains. The LED is a low voltage drive of 2 to 3 volts. It is necessary to design a complicated conversion circuit. LED lamps for different purposes must be equipped with different power adapters. In the international market, foreign customers have very high requirements for efficiency conversion, effective power, constant current accuracy, power supply life and electromagnetic compatibility of LED drive power . To design a good power supply, these factors must be considered comprehensively because the power supply is in the entire luminaire. The role is just as important as the human heart.

The LED drive 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 drive 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 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.

LED constant current drive

When using LEDs as displays or other lighting devices or backlights, they need to be driven with constant current. The main reasons are:

1. Avoid driving current exceeding the maximum rating and affect its reliability.

2. Obtain the expected brightness requirements and ensure the brightness and chromaticity of each LED

3. It can effectively avoid lightning strike, grid surge, over current, over voltage protection, and improve LED life.

There is a problem:

To deal with the heat dissipation problem, the heat dissipation problem will not affect the LED life.

At present, LEDs are all driven by DC, so a power adapter, that is, an LED driver, needs to be added between the mains and the LEDs. Its function is to convert AC mains into DC power for suitable LEDs. According to the power consumption rules of the power grid and the driving characteristics of the LED, the following points should be considered when selecting and designing the LED driver power supply:

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 especially important for structures where the power supply is installed in the luminaire. Since the luminous efficiency of the LED decreases as the temperature of the LED increases, the heat dissipation of the LED is very important. The power supply 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.

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