Constant duty cycle controlled discontinuous conduction mode (DCM) flyback power factor correction (PFC) converter has the advantage of high power factor (PF) and the disadvantage of low efficiency. While, constant on-time (COT) controlled critical conduction mode (CRM) flyback PFC converter has the exact opposite features, besides its switching frequency varies in a line cycle, and the variation range is very large, which complicates the electromagnetic interference (EMI) design. In order to obtain both benefits of these two control methods, an adaptive off-time (AOT) control technique for DCM flyback PFC converter is proposed in this paper. By utilizing the output voltage and the amplitude of line voltage to adjust the off-time of the main switch, the magnetizing current of transformer exactly operates in CRM when the rectified input voltage gets the peak. Thus, the root-mean-square (RMS) current of the main switch and the diode, as well as the conduction loss can be effectively reduced, and high efficiency can be obtained. The proposed control technique also can achieve theoretical unity PF over universal input voltage range of 90_264VAC. Moreover, its variation range of switching frequency is greatly reduced compared to that of COT control. A 60W prototype has been fabricated and tested in the laboratory and experimental results are presented to verify the effectiveness of the proposed method.
- Adaptive control
- Flyback converter
- Power factor
Figure 1. Block Diagram And Key Waveforms Of Aot Controlled Dcm Flyback Pfc Converter.
EXPECTED SIMULATION RESULTS:
Figure 2. The Rms Current Of The Main Switch And The Diode Of Flyback Pfc Converter With The Aforementioned Three Control Methods For Different Vin.
Figure 3. The Peak Current Of The Main Switch And The Diode Of Flyback Pfc Converter With The Aforementioned Three Control Methods For Different Vin.
Figure 4. Bode Plot Of Aot Control Loop.
This paper proposes an adaptive off-time controlled DCM flyback PFC converter. According to the output voltage and the amplitude of line voltage, the proposed controller adaptively adjusts the off-time of the main switch, so that the magnetizing current of the transformer can exactly operate in CRM. This operation mode can effectively reduce the conduction loss of the main switch and increase efficiency, and on the other hand, similar with constant duty cycle control, the duty cycle and the switch period of AOT control remains fixed during each line cycle, therefore, theoretical unity PF and sinusoidal input current can be also obtained over universal input voltage range. Moreover, the variation range of the switching frequency of AOT control strategy is greatly narrowed compared to that of COT control, which will bring potential convenience in the input filter design. A 60W experimental prototype has been built to verify the theoretical analysis. Experimental results show the minimal PF of AOT control and constant duty cycle control is 0.994, which is significantly higher the minimal PF 0.92 of COT control, and the highest efficiency of AOT control and COT control is 87.6%, which is obviously higher than the highest efficiency 86.5% of constant duty cycle control.
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