Switching Power Supply Sensing Circuit for Zero-Crossing and Overvoltage
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Solution Overview
Problem
Existing switching power supplies require additional pins for valley switching and have limited overvoltage protection, which can lead to safety issues and are not conducive to integrated design due to the reliance on a single stage of overvoltage protection.
Innovation Solution
A control circuit that utilizes a multiplexed detection pin to transmit sampling signals for inductor current, overcurrent, zero-crossing, and overvoltage information, allowing for integrated second-stage overvoltage protection without additional pins, using a combination of current sampling, differential, and voltage divider circuits to generate signals for control and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional pins are used for valley switching and overvoltage protection, then the protection functionality is improved, but the device complexity and pin quantity increase
Solution Approach 1:
The auxiliary winding is configured to provide multiple functions: it detects zero-crossing moments for valley switching control, generates overvoltage protection signals, and provides feedback for power factor correction. This multi-functional use of a single component eliminates the need for additional pins while maintaining comprehensive protection and control capabilities
Solution Approach 2:
The patent combines valley switching detection, overvoltage protection, and power factor correction functions into a single auxiliary winding and its associated detection circuit. By merging these functions that would traditionally require separate pins, the design achieves comprehensive protection without increasing pin quantity or device complexity
2Device complexity
If a single stage of overvoltage protection is used, then the device complexity is reduced, but the reliability and safety are insufficient
Solution Approach 1:
The control circuit dynamically adjusts switching control signals based on real-time detection of auxiliary winding signals. The circuit can adaptively respond to different operating conditions, load changes, and voltage variations, providing flexible and robust protection that effectively functions as multiple protection stages without the physical complexity of separate stages
3Measurement precision
If separate circuits are used for current sampling, zero-crossing detection, and overvoltage protection, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The detection circuit is segmented into functional modules that process different aspects of the auxiliary winding signal: zero-crossing detection module for valley switching, overvoltage detection module for protection, and power factor correction module for optimization. Each module maintains its detection precision while the overall structure remains integrated and compact
Solution Approach 2:
The auxiliary winding serves as an intermediary component that provides a single signal source containing information about current, voltage, and timing. This intermediary signal is then processed by the control circuit to extract multiple parameters, achieving precise measurement without requiring separate sensing circuits for each parameter
Data Source
AI summary
A control circuit for a switching power supply, can include: a sampling circuit configured to obtain an inductor current and a drain-source voltage of a main power transistor in a power stage circuit, in order to generate a sampling signal; where the control circuit generates an inductor current sampling signal according to the sampling signal during an on-period of the main power transistor; and where during an off-period of the main power transistor, the control circuit generates a zero-crossing signal of the inductor current and an overvoltage signal of an output voltage of the switching power supply according to the sampling signal.