The embedded boost power factor correction (PFC), which is realized by a storable duty cycle control method, has been verified that it can achieve good performance when the input voltage is standard sinusoidal signal. But the input current can not keep the good sinusoidal waveform all the time when the amplitude of the input voltage changes. In order to solve the problem, this paper presents a duty cycle adjustment strategy for embedded boost power factor correction. This strategy can adjust the duty cycle data synchronously when the amplitude of the input voltage changes. Its test results show that the adjustment strategy can achieve better performance to make the input current follow the shape and phase of the input voltage. The proposed duty cycle adjustment strategy can get the embedded boost power factor correction more effective and practical.
This paper proposes a new digital constant-current control method for high-power LED drive based on buck-boost topology. In this control system, buck-boost topology is used as the power conversion. The output voltage can be either higher or lower than the input voltage in buck-boost topology. Therefore, it solves the problem that in the buck topology the input voltage is required to be always higher than the output voltage. Furthermore, according to the input and output parameters, the duty cycle data which are used to maintain output current constant can be calculated in advance, and stored in the embedded chip. Thus, it can reduce the calculation of the embedded chip and solves the problem that the existing digital constant-current controllers need the high-speed analog-to-digital converter. In addition, in order to reduce the error generated in above calculation, the double threshold feedback circuit is used to fine-tune the duty cycle and makes the output current more steady and accurate. Meanwhile, due to adopting full-digital control, the brightness and flicker frequency of load LED can be conveniently regulated by modifying the system firmware. Therefore, this method can apply to the device of illumination, lighting decoration, visible light communication and so on.
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