Totem Pole PFC Synchronous Rectification for Freewheeling Loss Reduction
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Solution Overview
Problem
Totem pole power factor correction (PFC) systems lack a hardware-driven solution for synchronous rectification, leading to high system losses and reduced efficiency during freewheeling.
Innovation Solution
A synchronous rectification drive method and drive circuit for totem pole PFC, which includes providing specific PWM signals to control the switching transistors based on sampling voltages and predetermined voltages, thereby reducing losses during freewheeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a body diode is used for freewheeling in totem pole PFC, then the circuit structure is simple, but system losses are high and efficiency is reduced
Solution Approach 1:
The patent changes the operating parameters of the switching transistors by introducing synchronous rectification control. During freewheeling, the body diode is replaced by controlled switching of the transistor, changing the conduction state from passive diode to active transistor, thereby reducing voltage drop and power loss while maintaining circuit structure simplicity
Solution Approach 2:
The patent substitutes the passive body diode with an active switching transistor controlled by PWM signals. This replacement transitions from a passive mechanical-like component to an electronically controlled component, enabling precise control of current flow and significant reduction in conduction losses during freewheeling operation
2Loss of energy
If synchronous rectification control is implemented, then system efficiency is improved, but control complexity increases
Solution Approach 1:
The patent implements feedback control by detecting the state of switching transistors and adjusting PWM signals accordingly. The control circuit monitors transistor states and provides feedback to optimize the timing and duration of synchronous rectification, achieving efficient loss reduction while managing control complexity through intelligent feedback mechanisms
Solution Approach 2:
The patent employs periodic PWM signals to control the switching transistors during freewheeling. By using periodic control actions synchronized with the AC input cycle, the system achieves efficient synchronous rectification without requiring complex continuous control, thereby balancing efficiency improvement with acceptable control complexity
3Loss of energy
If PWM signals are provided to control switching transistors during freewheeling, then switching losses are reduced, but control circuit complexity increases
Solution Approach 1:
The patent makes the drive circuit universal by using the same PWM control mechanism for both main switching and synchronous rectification phases. The control circuit performs multiple functions including main switch control, synchronous rectification control, and freewheeling management, thereby reducing switching losses without proportionally increasing complexity through multi-functional integration
Data Source
AI summary
A synchronous rectification drive method and drive circuit for totem pole PFC are provided. The drive method includes: in a positive half-cycle, providing a first pulse width modulation (PWM) signal to the second switching transistor, switching on the fourth switching transistor, switching off the first and the third switching transistor first, and when a sampling voltage is greater than a predetermined first voltage, providing a second PWM signal to the first switching transistor, where the second PWM signal is opposite to the first PWM signal; and in a negative half-cycle, providing a third PWM signal to the first switching transistor, switching on the third switching transistor, switching off the second and the fourth switching transistor first, and when the sampling voltage is less than a predetermined second voltage, providing a fourth PWM signal to the second switching transistor, where the fourth PWM signal is opposite to the third PWM signal.