Soft Switching Synchronous Rectification Chopper Circuit
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Solution Overview
Problem
Conventional single-ended forward converters experience efficiency loss, generate noise, and require complex control circuits due to hard switching, while LLC resonant converters face issues with off-resonance and measurement errors, especially when handling weak signals.
Innovation Solution
A switching power supply apparatus with a synchronous rectification step-up/down chopper circuit, including a main switching element, choke coil, buffer capacitor, and commutation element, where the choke coil's inductance allows current flow in both directions within one cycle, and a switching control circuit provides complementary ON/OFF control with deadtime, along with a polarity detection circuit and ON-retention control, to achieve soft switching and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hard switching is used in single-ended forward converter, then the converter structure is simple and control is easy, but switching loss increases and efficiency decreases
Solution Approach 1:
The patent applies dynamic switching control where the main switching element and commutation element are complementarily turned ON/OFF with deadtime control. This dynamic operation allows the circuit to transition between different switching states, enabling soft switching conditions to be achieved while maintaining a relatively simple converter structure based on the single-ended forward topology.
Solution Approach 2:
The patent changes the switching mode parameter from hard switching to soft switching by introducing a commutation element and buffer capacitor. This parameter change in the switching operation mode reduces switching loss and improves efficiency while maintaining the basic converter structure.
2Device complexity
If hard switching is used in single-ended forward converter, then the converter structure remains simple, but noise generation increases
Solution Approach 1:
The dynamic complementary switching control of the main switching element and commutation element creates soft switching conditions that reduce electromagnetic interference and noise generation. The deadtime control ensures proper timing that prevents simultaneous conduction and reduces switching transients that cause noise.
Solution Approach 2:
The commutation element and buffer capacitor act as intermediary components that facilitate soft switching operation. These intermediary elements smooth the switching transitions and reduce the generation of noise and surge voltages while maintaining the basic converter structure.
3Loss of energy
If LLC resonant converter is used to achieve soft switching, then switching loss is reduced and efficiency is improved, but control circuit complexity increases
Solution Approach 1:
The patent extracts the resonance circuit components (L1, C1) from the traditional LLC resonant converter configuration and integrates them into a simplified control scheme. By taking out the complex frequency modulation control and using fixed frequency operation with duty cycle control, the patent reduces control circuit complexity while maintaining soft switching benefits.
Solution Approach 2:
The patent replaces the complex LLC resonant control circuitry with a simpler control approach using basic PWM control and deadtime generation. This substitution uses simpler, more economical control components while achieving the same soft switching effect, reducing overall system complexity.
4Reliability
If LLC resonant converter operates at variable frequency to maintain resonance, then soft switching is maintained, but measurement precision deteriorates due to off-resonance effects
Solution Approach 1:
The patent uses dynamic duty cycle control at fixed frequency to maintain soft switching operation. By dynamically adjusting the duty cycle of the main switching element while operating at a fixed resonant frequency, the system maintains reliable soft switching without the frequency variation that causes measurement errors and off-resonance effects.
Solution Approach 2:
The circuit uses the inherent resonance characteristics of the LC tank to automatically maintain soft switching conditions. The inductor L1 and capacitor C1 form a resonant circuit that naturally provides the soft switching environment, eliminating the need for complex frequency modulation control and avoiding measurement precision deterioration.
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 enables high-efficiency, low-noise operation with simplified control circuits, preventing surge voltages and allowing the use of low-withstand voltage semiconductor elements, while maintaining efficiency and reducing measurement errors, even under varying input and output conditions.
Implementation Method 1
a series circuit including a main switching element 14 and a choke coil 18 is connected in parallel with an input power supply 12
Implementation Method 2
a series circuit including a buffer capacitor 20 and a commutation element 16 is connected in parallel with the choke coil 18
Implementation Method 3
a synchronous rectifying element 108 and a flywheel-side synchronous rectifying element 110
Data Source
AI summary
A switching power supply apparatus is configured of, as a primary-side circuit, a synchronous rectification step-up/down chopper circuit including a main switching element (14), a commutation element (16), a choke coil (18), and a buffer capacitor (20). As a secondary-side circuit, to a secondary winding provided to the choke coil, a series circuit including a rectifying element and an output capacitor is connected. An inductance of the choke coil is set to have a predetermined value so that a choke coil current IL flowing through the choke coil flows in both of a positive direction and a negative direction across zero in one cycle of switching when an output current is equal to or smaller than a maximum output current. A switching control circuit performs control of complementarily turning the main switching element and the commutation element ON/OFF in a switching cycle by providing a deadtime, thereby performing soft switching.