Resonant Tank Current Sensing Circuit for High-Side Loss Reduction
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Solution Overview
Problem
Current current sensing methods in resonant tanks of switching power supplies face inefficiencies and limitations, particularly due to ohmic losses in resistor-based sensing and the inability of capacitor-based sensing to operate on the high side, leading to reduced efficiency and complex control circuits that increase costs.
Innovation Solution
A passive RC network comprising a sensing capacitor and resistor is used to accurately sense resonant tank current on both the high and low sides, enabling efficient and lossless current detection through differential voltage sampling across the resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistor-based sensing is used to detect resonant tank current, then current detection can be implemented, but ohmic losses occur that reduce converter efficiency
Solution Approach 1:
The patent introduces a capacitor as an intermediary element to sense the resonant tank current indirectly. Instead of placing a resistor directly in the current path (which causes ohmic losses), the capacitor is connected in parallel with the resonant capacitor, and the voltage across this sensing capacitor is proportional to the resonant tank current. This intermediary approach allows accurate current detection without the energy losses associated with direct resistive sensing.
2Loss of energy
If capacitor-based sensing is used to avoid ohmic losses, then efficiency improves, but the sensing circuit cannot operate on the high side requiring complex control circuits
Solution Approach 1:
The patent creates a universal sensing circuit that can operate on both the high side and low side of the converter. By designing the capacitor-based sensing circuit with appropriate switching control, the same basic topology can be applied regardless of whether the resonant tank is located on the high side or low side, eliminating the need for different sensing approaches and reducing overall system complexity.
Solution Approach 2:
The patent employs dynamic switching control to enable the capacitor-based sensing circuit to function in high-side applications. Through coordinated switching of the semiconductor devices, the sensing capacitor is selectively connected to the appropriate nodes during different switching intervals, allowing it to capture the resonant tank current information even when positioned on the high side where direct capacitive sensing would otherwise be infeasible.
3Ease of manufacture
If simple sensing circuits are used to reduce costs, then manufacturing cost decreases, but measurement precision and reliability are compromised
Solution Approach 1:
The patent uses inexpensive passive components (capacitors and resistors) to construct the sensing circuit, replacing complex and expensive active sensing solutions. The sensing circuit relies on basic RC network elements that are inexpensive, readily available, and easy to manufacture, while still providing accurate current measurement through the voltage-proportional relationship across the sensing capacitor.
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 method allows for precise and efficient detection of resonant tank current, ensuring stable converter operation, preventing overcurrent, and reducing costs by simplifying control schemes, thereby enhancing the reliability and efficiency of power converters.
Implementation Method 1
Through the resonance of Cr and Lr, a power device can be enabled to achieve ZVS and ZCS
Implementation Method 2
a voltage across the sense resistor is proportional to a current in the resonant circuit
Data Source
AI summary
A circuit is disclosed. The circuit includes a first semiconductor switch connected to a second semiconductor switch at a switch node, an input voltage coupled to the first semiconductor switch, a ground coupled to the second semiconductor switch, a resonant circuit coupled to the first and second semiconductor switches, the resonant circuit having an inductor in series with a resonant capacitor coupled to the input voltage, and a sense resistor, where a voltage across the sense resistor is proportional to a current in the resonant circuit. In one aspect, the circuit further includes a sense capacitor coupled between the resonant capacitor and the sense resistor. In another aspect, inductor is coupled in parallel with a resonant capacitor.