PFC ON-Time Control in DCM for High Power Factor
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Solution Overview
Problem
Existing power-factor-correction (PFC) power converters face inefficiencies when operating in discontinuous conduction mode (DCM), particularly due to high switching losses and reduced conversion efficiency at light or no-load conditions.
Innovation Solution
A PFC power converter with a power switch and an inductive device in series, controlled by a power controller with a compensation circuit, adaptation circuit, and ON-time controller. The adaptation circuit ensures a predetermined correlation between the ON time of the power switch, compensation signal, discharge time, and adapted compensation signal, maintaining an average input current proportional to the line voltage even in DCM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PFC circuit operates in critical mode with constant ON-time scheme, then power factor is improved, but switching loss increases significantly at light or no-load conditions
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed constant ON-time scheme to a dynamic control method where the ON-time is adjusted based on real-time detection of inductor current discharge status. The controller dynamically extends or reduces the ON-time of the power switch according to whether the inductor current has fully discharged, allowing the system to adapt to varying load conditions and minimize switching losses while maintaining power factor correction effectiveness.
2Reliability
If the ON time of power switch is kept constant, then power factor correction is achieved, but conversion efficiency decreases at light load conditions
Solution Approach 1:
The patent implements feedback by detecting the discharge status of the inductor current and using this information to adjust the ON-time of the power switch. The controller continuously monitors whether the inductor current has fully discharged before extending the ON-time, creating a closed-loop control system that optimizes conversion efficiency while maintaining power factor correction. This feedback mechanism prevents unnecessary switching cycles that would reduce efficiency at light load conditions.
3Speed
If the switching cycle is shortened to respond to light load conditions, then responsiveness is improved, but switching loss increases
Solution Approach 1:
The patent applies partial action by selectively extending the ON-time only when the inductor current has fully discharged, rather than continuously operating at maximum responsiveness. This partial extension of switching cycle duration reduces the switching frequency and minimizes switching losses, while still maintaining adequate responsiveness to load changes. The system performs the necessary switching action only when conditions permit, avoiding excessive switching that would increase energy loss.
Data Source
AI summary
A PFC power converter includes a power switch and an inductive device. A compensation signal is provided in response to an output voltage of the PFC power converter. An adapted compensation signal is provided in response to an ON time of the power switch and the compensation signal, to make the adapted compensation signal, the ON time, and the adapted compensation signal fit a predetermined correlation. The ON time of the power switch is determined in response to the adapted compensation signal. The PFC power converter is capable of achieving high PF when operating in discontinuous conduction mode.