AC Input Voltage Sensing for CrCM Boost Converter Protection
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Solution Overview
Problem
Existing boost power converters face challenges in achieving high switching frequencies and effective over-current protection while maintaining Critical Conduction Mode (CrCM) operation, leading to inefficiencies and limitations in power factor correction.
Innovation Solution
A fully digital, discrete-time control system that senses high-bandwidth bidirectional inductor current in a totem-pole converter, compares it against programmable thresholds, and adjusts synchronous rectifier conduction time based on pulse counting, enabling CrCM control and over-current protection, while allowing for higher switching frequencies and efficient power factor correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing methods are used in boost power converters, then device complexity is reduced, but measurement precision of inductor current is insufficient for high switching frequencies and CrCM control
Solution Approach 1:
The current sensing function is segmented and distributed to individual switches rather than using a centralized sensing method. Each switch has its own current sensing capability, allowing precise measurement of inductor current at different stages of the switching cycle while maintaining modular circuit architecture.
Solution Approach 2:
The patent uses voltage sensing across the switch as an intermediary method to indirectly measure inductor current. By measuring the voltage across the switch during specific time intervals, the system can derive accurate current information without requiring direct current sensors, thus reducing complexity while maintaining precision.
2Productivity
If higher switching frequencies are implemented, then productivity increases, but over-current protection becomes more difficult to achieve effectively
Solution Approach 1:
The system performs preliminary current assessment by sensing voltage across the switch before the switching event occurs. This allows the control logic to predict potential over-current conditions and adjust switching timing or duty cycle in advance, preventing over-current damage while enabling higher switching frequencies.
Solution Approach 2:
The patent implements real-time feedback through continuous voltage sensing across the switch, which provides immediate information about current conditions. This feedback loop allows the control system to dynamically adjust switching parameters to maintain safe operating limits even at elevated switching frequencies.
3Productivity
If CrCM control is implemented with precise current sensing, then power factor correction efficiency improves, but device complexity increases
Solution Approach 1:
The system uses the switch's own voltage characteristics to provide current sensing information needed for CrCM control. The voltage across the switch during conduction naturally provides the information required to determine when the inductor current reaches zero, enabling automatic CrCM operation without requiring additional complex sensing circuits or external components.
Data Source
AI summary
A method of detecting zero crossings in an AC input voltage at an input of a power converter, including measuring, at a first time, a first voltage. If the first voltage is positive, the method may include determining that the first time corresponds to a positive half-cycle of the AC input voltage. If the first voltage is equal to approximately zero: a) determining that the first time corresponds to a negative half-cycle of the AC input voltage; b) turning on a high-side switch of the power converter for a first time period; and c) measuring, during the first time period, a second voltage. If the second voltage is less than a first threshold, turning off the high-side switch and repeating b) and c) after a time delay. If the second voltage is less than a second threshold, maintaining the high-side switch in an ON state for a second time period.