Synchronous Rectifier Feedback Control to Prevent Cross-Conduction
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Solution Overview
Problem
Current synchronous rectification technologies in switching power supply circuits face challenges in preventing simultaneous conduction between the primary and secondary circuits, especially under dynamic loads and rapid input voltage switching, leading to reliability issues and potential breakdowns.
Innovation Solution
A synchronous rectification switching power supply circuit with a monitoring circuit that real-time monitors the operating conditions of the secondary side output rectification circuit, controlling the primary switching transistor to be on only when the secondary side is in an off state, thereby preventing conduction during the 'on' period of the secondary synchronous rectifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous rectification control techniques (slope detection, integration) are used to distinguish primary PWM switching waveforms from transformer excitation waveforms, then the ability to prevent simultaneous conduction is improved under normal conditions, but reliability deteriorates under extremely large dynamic loads and rapid input voltage switching
Solution Approach 1:
The patent implements a feedback mechanism where the controller receives real-time status information from the synchronous rectifier tube and adjusts the primary switching transistor control accordingly. The controller determines whether the synchronous rectifier tube is in conduction state and forbids activation of the primary switching transistor during this period, creating a closed-loop control system that adapts to varying load conditions and prevents simultaneous conduction reliably.
Solution Approach 2:
The patent applies preliminary action by proactively determining the conduction state of the synchronous rectifier tube before allowing the primary switching transistor to activate. The controller uses status information from the synchronous rectifier tube to preemptively prevent simultaneous conduction by controlling the primary switching transistor based on real-time conditions, rather than reacting after the problem occurs.
2Reliability
If preventive measures based on assumptions are implemented in the synchronous rectifier controller, then simultaneous conduction is avoided under those specific conditions, but the measures fail when assumptions do not hold, leading to primary switching transistor turn-on during secondary synchronous rectifier 'on' period
Solution Approach 1:
The patent replaces assumption-based preventive measures with a feedback-based control system. The controller continuously receives actual status information from the synchronous rectifier tube and adjusts control decisions based on real conditions rather than predefined assumptions. This feedback mechanism ensures reliable prevention of simultaneous conduction across varying operating conditions without requiring complex assumption-based logic.
3Loss of energy
If low closure resistance switching transistor is used to replace diode for rectification, then circuit closure loss is reduced and efficiency is improved, but reliability deteriorates and simultaneous conduction becomes more prone to occur
Solution Approach 1:
The patent maintains the low closure resistance switching transistor for efficient rectification while adding a feedback-based control system that monitors the synchronous rectifier tube status and prevents simultaneous conduction. The controller uses real-time status information to reliably control the primary switching transistor, ensuring that the efficiency benefits of low closure resistance are achieved without sacrificing reliability.
Data Source
AI summary
In a synchronous rectification switching power supply circuit and a control method for a primary switching transistor and an electronic device, one end of a first switching transistor is coupled to a transformer, and the other end thereof is grounded; a second end and a third end of the transformer are respectively coupled to a first end of the first capacitor and a first end of the second switching transistor; a second end of a second switching transistor is coupled to a second end of a first capacitor; a first resistor is connected in parallel with the first capacitor; and a monitoring circuit is coupled to the switching transistor control unit in such a manner that the operating condition of the secondary side output rectification circuit is monitored in real-time by the monitoring circuit.