Flyback Converter Passive Clamp Leakage Loss Reduction
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Solution Overview
Problem
Flyback converters face limitations in developing smaller sizes and higher frequencies due to leakage loss of the transformer and turn-on loss of the main switch, which restricts their efficiency and performance.
Innovation Solution
The converter incorporates a transformer, a main switch, an active or passive clamping circuit, a synchronous rectifying switch, and a processing circuit that determines the conducting periods of the synchronous rectifying switch to generate appropriate driving signals, thereby controlling the switch operations and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency is increased to reduce converter size, then the power density is improved, but the leakage loss of the transformer increases
Solution Approach 1:
The patent recycles the energy stored in the transformer leakage inductance by using a clamping circuit to redirect it through a diode and capacitor back to the output, converting the harmful leakage loss into useful energy that contributes to the output voltage, thereby reducing overall energy loss while enabling higher switching frequencies
Solution Approach 2:
The patent introduces additional circuit elements (clamping capacitor, diode, and control switches) that change the electrical parameters of the system by providing an alternative energy path, which allows the converter to operate at higher frequencies with reduced leakage losses
2Productivity
If the switching frequency is increased to reduce converter size, then the power density is improved, but the turn-on loss of the main switch increases
Solution Approach 1:
The clamping circuit is activated before the main switch turns on to pre-charge the clamping capacitor and establish the clamping voltage, ensuring that when the main switch closes, the voltage across it is already limited, thereby reducing turn-on losses
Solution Approach 2:
The circuit converts the potentially harmful high voltage across the main switch during turn-on into a controlled, lower voltage by using the clamping mechanism, thereby reducing turn-on losses while maintaining high switching frequency operation
3Loss of energy
If a passive clamping circuit is used to reduce leakage loss, then the energy efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent uses simple, passive components (diodes, capacitors, and resistors) in the clamping circuit that are inexpensive and easy to implement, accepting that these components add some complexity but using readily available, low-cost parts to minimize overall system cost and complexity
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 solution enhances the efficiency and safety of the converter by minimizing conversion losses and preventing burn-out, allowing for smaller size and higher frequency operations while maintaining efficient energy transfer.
Implementation Method 1
The transformer includes a primary winding and a secondary winding
Implementation Method 2
The main switch is electrically coupled to the primary winding
Implementation Method 3
The synchronous rectifying switch is electrically coupled to the secondary winding
Data Source
AI summary
A converter includes a transformer, a main switch, an active clamping circuit, a synchronous rectifying switch and a processing circuit. The transformer includes a primary winding and a secondary winding. The main switch is coupled to the primary winding. The active clamping circuit clamps the voltage across the main switch when it is OFF. The active clamping circuit includes an auxiliary switch. The synchronous rectifying switch is coupled to the secondary winding. The processing circuit determines whether the rectifying switch is in a main conducting period or a sub conducting period according to a first voltage signal across the rectifying switch and at least one detecting signal from the converter, and generates a driving signal to control the synchronous rectifying switch accordingly.