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Multi-Phase Adaptive On-Time Controlled PFC for Better Light Load Efficiency and EMI Performance

Fig. 1. Adaptive phase angle control.
With the fast growing information technologies, high efficiency and high power density become the two major challenges for AC-DC front-end power supplies in all kinds of distributed power system. For the power factor correction (PFC) stage, the adaptive on-time control was proposed to achieve high efficiency over the whole load range. In order to reduce the EMI noise, the multi-phase interleaving approach is applied to the adaptive on time PFC. Unlike the multi-phase method using other control methods, the phase-shading operation is not needed for the multi-phase adaptive on time control since the light load efficiency has already been greatly improved. Since the switching frequency the adaptive on time control is a variable, the novel adaptive phase angle control is proposed to achieve the best noise cancellation effect. In different frequency range, the phase shift angle is changed accordingly to cancel the noise at 150kHz, which is the starting frequency of EMI standard. Experiment results show that the multi-phase adaptive on time PFC can achieve 50% EMI filter size reduction while keeping high efficiency over the whole load range.

Fig. 2. DM noise comparison.
Fig. 3. Efficiency comparison.
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