Switching Power Supply with Secondary Switching Elements
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Solution Overview
Problem
Existing full-bridge switching power supply devices experience high switching loss due to the slow operation of high-voltage N-channel MOS-type FETs, leading to significant energy inefficiency and heat generation.
Innovation Solution
A full-bridge switching power supply device configuration with a secondary switching element that turns on for a predetermined time during the on/off periods of the primary switching elements, utilizing a transformer with a single primary coil and multiple secondary coils, and a control circuit that adjusts the on/off timing based on detected voltage and current differences to minimize switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high-voltage N-channel MOS-type FETs are used as switching elements, then the device can operate at high voltage, but the switching speed becomes slow and switching loss increases significantly
Solution Approach 1:
The patent divides the switching function into two separate stages: primary switching elements (Q1-Q4) that handle voltage transformation through the transformer, and secondary switching elements (Q5-Q10) that handle the actual power switching at lower voltage. This segmentation allows each stage to use switching elements optimized for its specific voltage level and speed requirements, resolving the contradiction between high voltage operation and fast switching speed.
Solution Approach 2:
The transformer serves as an intermediary device between the primary switching stage and the secondary switching stage. It isolates the high-voltage primary circuit from the low-voltage secondary circuit, enabling the use of fast-switching low-voltage FETs in the secondary stage without being constrained by high-voltage limitations, thus reducing overall switching loss while maintaining high voltage capability.
2Device complexity
If a simple circuit with reduced number of components is used, then device complexity is lowered, but switching loss increases due to slow switching elements
Solution Approach 1:
The circuit is segmented into primary and secondary switching stages with distinct functions. The primary stage uses a simple full-bridge configuration with 4 switching elements, while the secondary stage adds 6 controlled rectifying elements. This segmentation allows the overall circuit to achieve low switching loss through the secondary stage's fast switching, while the primary stage maintains simplicity, balancing complexity and efficiency.
Solution Approach 2:
The secondary switching elements (Q5-Q10) serve multiple functions: they act as controlled rectifiers, voltage regulators, and switching elements simultaneously. This multi-functionality allows the circuit to achieve sophisticated power control and low switching loss without proportionally increasing circuit complexity, as these elements perform several critical roles in the power conversion process.
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 significantly reduces switching loss by using faster secondary switching elements, improving efficiency and reducing heat generation, while allowing power supply to multiple loads with a single device.
Implementation Method 1
a transformer having a single primary coil and an N (N is an integer of 1 or above) number of secondary coils
Implementation Method 2
a rectifier circuit configured to rectify a commercial AC voltage to be converted into a DC voltage
Data Source
AI summary
Provided is a switching power supply device having a very small switching loss, which includes a rectifier circuit for rectifying a commercial AC voltage, a full-bridge circuit having first to fourth switching element, a transformer having a single primary coil and an N number of secondary coils, an N number of rectifying and smoothing circuits, an output detecting circuit for detecting at least one of voltage and current output from each rectifying and smoothing circuit, and a control circuit. Each rectifying and smoothing circuit includes a rectifying unit, a secondary switching element for controlling an output of the rectified voltage, and a smoothing unit for smoothing the rectified voltage, and the control circuit turns on each secondary switching element during a predetermined time.