Isolated Switching Converter Control for Full Zero-Voltage Switching
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Solution Overview
Problem
Existing isolated power supplies face challenges in meeting the higher power delivery requirements of USB PD standards while maintaining high efficiency and low cost, as silicon-based devices approach their theoretical performance limits.
Innovation Solution
An isolated switching converter with a controller that includes a maximum sense circuit, voltage divider, timer, and ON-time control circuit to dynamically adjust the secondary switch's ON-time, ensuring full zero-voltage switching by comparing the current switching cycle's time interval with a predefined threshold, using wide bandgap devices like GaN or SiC to reduce output capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based devices are used in isolated power supplies, then cost is reduced, but performance improvements become difficult as theoretical limits are approached
Solution Approach 1:
The patent changes the material parameter from silicon-based devices to wide bandgap devices (GaN or SiC), which fundamentally alters the electrical characteristics including higher breakdown voltage, lower on-resistance, and higher switching frequency capability. This material parameter change enables achieving higher power density and efficiency while maintaining cost-effectiveness through advanced device physics rather than incremental silicon optimization.
2Power
If higher power delivery is implemented to meet USB PD standards, then power capability increases, but efficiency and size constraints become more difficult to maintain
Solution Approach 1:
The patent employs high-frequency periodic switching action using wide bandgap devices operating at switching frequencies significantly higher than traditional silicon devices. This periodic switching enables higher power delivery while maintaining efficiency through reduced conduction and switching losses, allowing the use of smaller magnetic components and capacitors that would otherwise be required to achieve the same power level.
Solution Approach 2:
By changing the device material parameter to wide bandgap semiconductors, the patent achieves lower on-resistance and higher breakdown voltage, which directly reduces conduction losses and enables higher efficiency at elevated power levels. The higher electron saturation velocity in GaN and SiC also reduces switching losses, maintaining efficiency even as power delivery capability increases.
3Volume of moving object
If higher switching frequency is used to reduce size, then power density increases, but switching losses and electromagnetic interference increase
Solution Approach 1:
The patent changes the switching device material to wide bandgap semiconductors, which enable operation at much higher switching frequencies with lower switching losses compared to silicon devices. The higher electron saturation velocity and lower parasitic capacitance in GaN and SiC devices reduce the energy lost during switching transitions, allowing high-frequency operation that shrinks magnetics and capacitors while maintaining acceptable EMI levels through more efficient switching.
Data Source
AI summary
A controller used in an isolated switching converter with a transformer, a primary switch and a secondary switch, the controller has a maximum sense circuit for providing a first voltage signal representative of a maximum value of a first voltage across the secondary switch, and a timer for starting timing when the first voltage increases to a second voltage signal less than the first voltage signal and stop timing when the first voltage increases to the first voltage signal, and the timing duration of the timer is a first time interval. The secondary switch is turned on for a second ON-time after a current flowing through the secondary switch decreases to zero. The second ON-time of the secondary switch is adjusted so that the first time interval of the next switching cycle is close to a first time threshold.