Resonant Converter Current Sensing via Capacitor Voltage Sampling
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Solution Overview
Problem
Conventional resonant converters face challenges in cost-effective current sensing due to the use of current transformers, which incur high costs and induce significant power loss when using sensing resistors.
Innovation Solution
A resonant converter design incorporating a current sensing circuit that samples the voltage at one end of the resonant capacitor, performs high-pass filtering, and limits negative voltages to provide a current sensing signal, eliminating the need for additional sensing devices in the resonant tank circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current transformer is used for sensing resonant current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current sensing function from the traditional current transformer approach and implements it through voltage sampling of the resonant capacitor. By sampling the voltage across the resonant capacitor and processing it through filtering and rectification circuits, the system obtains current information without requiring a current transformer, thus reducing device complexity while maintaining measurement capability
Solution Approach 2:
The patent creates a voltage copy of the resonant current information by sampling the capacitor voltage, which is proportional to the current. This voltage copy is then processed through filtering and rectification to reproduce the current waveform characteristics, enabling current sensing without direct current measurement
2Measurement precision
If a sensing resistor is used for current sensing, then measurement precision is improved, but power loss increases
Solution Approach 1:
The patent introduces the resonant capacitor voltage as an intermediary parameter to sense the resonant current. Instead of directly measuring current through a sensing resistor, the system measures the voltage across the capacitor, which is naturally present in the resonant circuit and provides current information without introducing additional power loss
3Measurement precision
If a current transformer is used, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent replaces the expensive current transformer with inexpensive passive components including capacitors, resistors, and diodes arranged in filtering and rectification circuits. These components are significantly cheaper than current transformers while achieving the same current sensing function through voltage sampling and signal processing
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 approach reduces power loss and costs associated with resonant current sensing while accurately characterizing the current flowing through the resonant tank circuit, enhancing efficiency and reliability.
Implementation Method 1
The resonant tank circuit receives the square wave signal and generates an approximately sinusoidal resonant current
Implementation Method 2
performs high-pass filtering, and limits negative voltages to provide a current sensing signal
Data Source
AI summary
A resonant converter has a first transistor, a second transistor, a third transistor, a fourth transistor, a transformer, a resonant tank, a rectifier circuit and a current sensing circuit. The transformer comprises a primary winding and a first sampling winding at a primary side, and a secondary winding at a secondary side. The resonant tank circuit is coupled between the first switching node and the second switching node and comprises a resonant capacitor, a resonant inductor and a magnetizing inductance of the primary winding coupled in series. The rectifier circuit is coupled between the first end of the secondary winding and the second end of the secondary winding. The current sensing circuit is used to receive the first capacitor voltage sampling signal and provide a current sensing signal based on the first capacitor voltage sampling signal.