Synchronous Rectifying Forward Converter Oscillation Control
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Solution Overview
Problem
Conventional synchronous rectifying forward converters experience abnormal and self-excited oscillations due to backflow operations caused by output overvoltage, leading to instability and inability to absorb reverse currents effectively.
Innovation Solution
The implementation of a synchronous rectifying forward converter with a transformer having a primary, secondary, and tertiary winding, along with a choke coil, smoothing capacitor, and synchronized rectifying and commutating switch elements, driven by a sophisticated switching control circuit that includes pulse transformers and a synchronous rectifier element driving circuit to manage ON/OFF timings and control voltages, ensuring reliable operation and preventing oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the main switch element stops switching operation, then the normal operation is maintained, but backflow causes self-excited oscillation on the secondary side
Solution Approach 1:
The patent uses feedback control where the drive signal for the synchronous rectifier elements is continuously monitored and adjusted based on the state of the main switch element and the presence of backflow conditions. This ensures that when backflow occurs, the rectifier elements are properly controlled to prevent self-excited oscillation.
Solution Approach 2:
The patent applies preliminary anti-action by preparing the synchronous rectifier elements to handle backflow conditions before they occur. The drive signal is designed to anticipate backflow events and pre-position the rectifier elements in a state that prevents self-excited oscillation when backflow actually occurs.
2Productivity
If the rectifying-side synchronous rectifier element is turned OFF by inversion of voltage, then the normal rectification is achieved, but during backflow the element remains ON, causing abnormal oscillation
Solution Approach 1:
The patent implements feedback control where the drive signal for the rectifying-side synchronous rectifier element is continuously adjusted based on the operational state. During backflow conditions, the feedback mechanism detects the abnormal state and modifies the drive signal to properly turn OFF the rectifier element, preventing abnormal oscillation while maintaining normal rectification efficiency during standard operation.
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
This configuration effectively prevents abnormal and self-excited oscillations, ensures stable operation, and allows for the absorption of backflow currents without increasing the ON-period of the transformer, thereby maintaining voltage stability and preventing self-excited oscillations.
Implementation Method 1
a transformer (T1) including a primary winding, a secondary winding, and a tertiary winding; a main switch element (Q1) connected in series to the primary winding of the transformer (T1)
Implementation Method 2
a choke coil (L2) connected in series to the secondary winding (N2) of the transformer (T1)
Data Source
AI summary
A first drive control signal regenerating circuit outputs an ON timing drive signal at turn-ON of a main switch element, and a second drive control signal regenerating circuit generates an OFF timing drive signal at turn-OFF of the main switch element. A rectifying switch controlling switch element connected between the gate and source of a rectifying switch element is driven by an output of the second drive control signal regenerating circuit. An output of the first drive control signal regenerating circuit connects to the gate of a commutating switch controlling switch element, which connects to one end of an auxiliary winding, the other end thereof being connected to the gate of a commutating switch element. Accordingly, the rectifying switch element is directly controlled from the primary side.