LED driver circuit: technology upgrade pursues efficiency

The drive circuit is an important part of LED (light-emitting diode) products, and its technical maturity is gradually increasing with the expansion of the LED market . Whether in the field of lighting, backlighting or display panels, the choice of drive circuit technology architecture should match the specific application.

As the backlight of LCD (liquid crystal display), LED's position in portable products is unshakable. Even in the backlight of large-size LCD, LED has begun to challenge the mainstream status of CCFL (Cold Cathode Fluorescent Lamp); As the most critical component of semiconductor lighting, LED is sought after by the market for its aura of energy saving, environmental protection, long life and maintenance-free. However, people have been concerned about how many "supporting actors" are silently contributing behind the dazzling "stars"? The LED driver circuit is such a "behind the scenes".

Drive technology is gradually upgraded

The LED's illumination mechanism is to apply a forward voltage across it to recombine minority carriers and majority carriers in the semiconductor, releasing excess energy, causing photon emission. The main function of the LED driver circuit is to convert the AC voltage into a constant current source, and at the same time complete the matching with the voltage and current of the LED according to the requirements of the LED device. Taking white LEDs as an example, white LEDs require a supply voltage of approximately 3.6 volts to achieve proper brightness control. However, most portable electronic products use lithium-ion batteries as the power source. They are about 4.2 volts after being fully charged, and about 2.8 volts after being safely discharged. Obviously, white LEDs cannot be directly driven by the battery, so a boost circuit is needed. The LED is stably powered continuously throughout the battery life cycle.

In addition, many product designers hope that the brightness of the LED can be changed in different applications, and this task will be handed over to the driver circuit. PWM (Pulse Width Modulation) technology is a traditional dimming method that uses a simple digital pulse to repeatedly switch the LED driver . The system only needs to provide wide and narrow digital pulses to easily change the output current. Thereby adjusting the brightness of the LED. The advantage of this technology is that it can provide high quality white light, as well as simple application and high efficiency, but a fatal shortcoming is that it is easy to generate electromagnetic interference, and sometimes even the noise that can be heard by the human ear. Yan Shiyan, CEO of Beijing Siwang Electronic Technology Co., Ltd. introduced digital dimming technology, which can control LED brightness in real time and avoid electromagnetic interference.

At the same time as "the job" is completed, some manufacturers have integrated some additional functions in the LED driver circuit, such as audio amplifiers. Ling Hui, general manager of China Resources Converse Technology (Shanghai) Co., Ltd., said that many companies are currently engaged in the design of PMU (Power Management Unit), which integrates some analog functions into a single chip as much as possible. Some contributions have been made in saving PCB (printed circuit board) space, improving reliability, reducing costs, etc., but whether this is required or not depends on the needs of the product application.

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