LED lighting has become the focus of everyone's attention because of its high energy saving, long life and environmental protection. In recent years, the high-brightness LED light source has experienced rapid advancement in its manufacturing technology, and its production cost has been declining. Nowadays, the use of LED light source as a high-brightness, high-efficiency, energy-saving, carbon-free energy-saving lighting source has become a global mass. Demand, an emerging industry that manufactures LED lighting is on the rise, the industry chain is getting better and better, and technology is being updated every day.
BP2808 basic working principle
The BP2808 is a constant current control chip that specifically drives LED light sources. The BP2808 operates in a continuous current mode step-down system. The chip controls the peak current and ripple current of the LED source to achieve a constant average current of the LED source. The chip implements constant current control, analog dimming, and PWM dimming with very few external components. The system application voltage ranges from 12VDC to 600VDC, and the duty cycle can be up to 100%. It is suitable for AC 85V-265V wide voltage input, mainly used for non-isolated LED lamp power drive system. The BP2808 uses a patented source drive and constant current compensation technology to make the current driving the LED source constant, varying less than ±3% from AC 85V-265V. Combined with BP2808 patented drive system application circuit, the 18W LED fluorescent lamp practical solution has a system efficiency higher than 90% in the range of AC 85V-265V. In the AC 85V-265V input range, the BP2808 can drive LED light source arrays from 3W to 36W, so it is widely used in E14/E27/PAR30/PAR38/GU10 and other LED and LED fluorescent lamps.
The BP2808 features multiple LED protection features including LED open circuit protection, LED short circuit protection, and over temperature protection. Once a system failure occurs, the power system automatically enters the protection state until the fault is removed and the system automatically re-enters the normal operating mode. Multiplexed DIM pins allow for LED analog dimming, PWM dimming, and dynamic temperature protection of the fixture system. The BP2808 is available in an SOP8 package.
Typical design of LED fluorescent lamp application
There are many kinds of LED light source strips for LED fluorescent lamps. At present, non-isolated schemes are dominant because of their high efficiency, small size and low cost, while the majority of LED fluorescent controllers are used to drive LED fluorescent lamps. . In fact, traditional fluorescent fluorescent lamps are non-isolated solutions.
Taking the AC176V-264V full-voltage input as an example, BP2808 is used as the main chip to design a multi-string and multi-integrated LED fluorescent lamp with low power and multiple LED light sources. The block diagram of the whole system scheme is shown in Figure 1. The whole circuit is protected by surge/lightning protection, EMI filtering, full bridge rectification, passive power factor correction (PPFC), starting voltage (including feedforward compensation, feed power supply after power on, drive softening), constant current compensation, PWM control, source drive, LED light source array, and sampling resistor, Toff time setting, energy storage inductor, freewheeling diode and other components.
Figure 1: Block diagram of the 18W LED fluorescent system design.
The LED light source array is designed as a 0.06W white LED (SMT or straw hat) with 24 series and 12 series parallel schemes, driving 288 low power WLEDs with a total power of 18W. The design circuit of the constant voltage source of the full voltage 18W LED fluorescent switch is shown in Figure 2. The functions of each part are marked by the red letter. The anti-lightning and EMI filtering in the figure constitutes an EMC circuit, and the feed current is realized by using a rectifying diode that has been implemented inside the chip.