PFC Burst Mode Control Without AC Input Voltage
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Solution Overview
Problem
Digital power supply controllers face challenges in implementing average current mode CCM-DCM power factor correction (PFC) control during burst mode without AC input voltage measurements, due to resource conflicts and safety requirements that limit the availability of AC input voltage measurements.
Innovation Solution
A digital controller that operates the PFC stage in continuous-conduction mode (CCM) using a current control loop during steady-state and in discontinuous-conduction mode (DCM) during burst mode using a voltage control loop, with an adaptive loop that modifies the voltage control loop based on the output of the voltage mode controller to maintain power within predetermined limits, and adjusts the DC equivalent value of the AC input voltage measurement to ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC input voltage measurement is used for current mode control during steady-state, then current regulation accuracy is improved, but during burst mode the measurement may not be available due to resource conflict with AC detection feature
Solution Approach 1:
The patent segments the control operation into two distinct modes: current mode control for steady-state operation and voltage mode control for burst mode operation. This segmentation allows each mode to use the most appropriate control strategy available for its specific operating conditions, resolving the contradiction by ensuring current regulation accuracy when measurements are available and maintaining adaptability when they are not.
Solution Approach 2:
The patent dynamically switches between current mode control and voltage mode control based on the operating mode (steady-state vs. burst mode). This dynamic adaptation allows the system to optimize performance for each specific condition, maintaining current regulation accuracy during steady-state while ensuring proper operation during burst mode when AC input voltage measurements may not be available.
2Device complexity
If a single pin is used for both AC input voltage measurement and AC detection, then pin count is reduced, but AC input voltage measurement may not be available during burst mode due to resource conflict
Solution Approach 1:
The patent makes the single pin universal by allowing it to serve both AC input voltage measurement and AC detection functions. The pin is configured to perform AC input voltage measurement during steady-state mode and AC detection during burst mode, eliminating the need for separate pins while ensuring the appropriate function is available when needed.
Solution Approach 2:
The pin's function is dynamically changed based on the operating mode. During steady-state, the pin is configured for AC input voltage measurement to support current mode control. During burst mode, the pin is reconfigured for AC detection to meet safety requirements. This dynamic reconfiguration resolves the resource conflict while maintaining both functionalities.
3Adaptability or versatility
If voltage mode control is used during burst mode without AC input voltage measurements, then adaptability is improved, but power regulation precision may deteriorate
Solution Approach 1:
The patent segments the regulation precision requirements by control mode: current mode control provides high precision current regulation during steady-state, while voltage mode control provides adequate power regulation during burst mode. The segmentation allows each mode to meet its specific precision requirements without compromising the other.
Solution Approach 2:
The patent implements feedback mechanisms in both control modes to maintain regulation precision. During steady-state, current mode feedback ensures accurate current regulation. During burst mode, voltage mode feedback with adaptive on-time adjustment ensures stable power regulation despite the lack of AC input voltage measurements, thus maintaining adequate precision in both modes.
Data Source
AI summary
A method of operating a power supply having a PFC stage and an LLC converter coupled to the PFC stage includes: operating the PFC stage in CCM in a steady-state mode of the power supply using a current mode controller, by implementing a current control loop which has AC input voltage measurements as an input; operating the PFC stage in DCM for at least part of a burst mode of the power supply using a voltage mode controller, by implementing a voltage control loop which does not have AC input voltage measurements as an input; and modifying the voltage control loop if an output of the voltage mode controller in burst mode and which is proportional to power in average current mode control falls outside a predetermined range.