CrCM Boost Converter Control for Over-Current and High-Frequency PFC
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Solution Overview
Problem
Boost power converters operating in Critical Conduction Mode (CrCM) face challenges in efficiently regulating peak inductor current and preventing over-current conditions, while conventional methods struggle to maintain high switching frequencies and effective power factor correction.
Innovation Solution
A power factor correction circuit that senses high-bandwidth bidirectional inductor current using current-sense resistors, 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 current sharing between phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current sensing methods are used in CrCM boost converters, then the circuit complexity is reduced, but the ability to prevent over-current conditions and enable higher switching frequencies is compromised
Solution Approach 1:
The current sensing function is segmented and distributed to each switch node, with individual current-sense resistors placed in series with each switch. This allows independent monitoring of current at different switching nodes, enabling precise over-current detection and protection while maintaining CrCM operation at higher frequencies.
Solution Approach 2:
Current-sense resistors are introduced as intermediary elements between the inductor and switch nodes. These resistors convert current information into voltage signals that can be processed by the digital controller, enabling high-bandwidth bidirectional current sensing without directly complicating the main power path.
2Productivity
If higher switching frequencies are implemented, then the power converter size is reduced, but the over-current protection capability and CrCM control precision deteriorate
Solution Approach 1:
A digital feedback control system continuously monitors the inductor current through current-sense resistors and compares it against reference thresholds. The controller adjusts the switch duty cycles in real-time to maintain CrCM operation precisely, even at higher switching frequencies, ensuring that the inductor current reaches zero at the end of each switching cycle.
Solution Approach 2:
Over-current protection thresholds are pre-configured in the digital controller, and current monitoring is performed continuously before over-current conditions can develop. The system is prepared to interrupt switching sequences proactively when current approaches unsafe levels, preventing damage while maintaining high-frequency operation.
3Measurement precision
If bidirectional current sensing is implemented, then the power factor correction accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The current sensing function is merged with the existing switch node structure, utilizing the same physical location and control infrastructure. Current-sense resistors are integrated into the switch node circuitry, allowing bidirectional current measurement without adding separate sensing circuits. The digital controller processes both positive and negative current directions using the same hardware platform.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution prevents over-current conditions, enables higher switching frequencies, and ensures efficient power factor correction, maintaining CrCM operation and effective current regulation across varying input voltages.
Implementation Method 1
An apparatus (e.g., implemented as a circuit) to sense high bandwidth bidirectional inductor current in a totem-pole converter (e.g., a bridgeless totem-pole boost PFC converter) using current-sense resistor based per-switch, current-sensing.
Data Source
AI summary
A method of setting a synchronous rectifier on-time value includes determining that a time interval has occurred, receiving a number of triangular current mode (TCM) pulses measured during the time interval, and determining a pulse comparison value equal to a number of switching period pulses during the time interval minus the number of TCM pulses during the time interval. The method also includes increasing the synchronous rectifier on-time if the pulse comparison value is greater than or equal to a threshold and decreasing the synchronous rectifier on-time if the pulse comparison value is less than the threshold.