Capacitive Current Divider for Accurate DC-DC Converter Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for sensing current in DC-DC converters, such as using DC resistors or Hall Effect sensors, result in inefficiencies, increased costs, or limited bandwidth and accuracy, particularly in switched power converters.
Innovation Solution
A current divider circuit using a sense capacitor coupled with a resonant capacitor, coupled to a transimpedance amplifier with a current feedback configuration, which generates a voltage output proportional to the sense current, improving bandwidth and stability without the need for additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC resistor is added in the primary circuit for current sensing, then current measurement is achieved, but power loss increases and efficiency decreases
Solution Approach 1:
The patent introduces a sense capacitor as an intermediary component that indirectly measures the primary current through capacitive coupling. Instead of placing a resistor directly in the high-current path (which causes power loss), the sense capacitor couples to a capacitive node and provides a scaled-down version of the current waveform that can be measured with minimal power dissipation.
Solution Approach 2:
The sense capacitor creates a copy of the primary current waveform through capacitive coupling. The current through the sense capacitor is proportional to the primary current but scaled down by the capacitance ratio, allowing accurate measurement without the need to handle full primary current levels, thus reducing power loss.
2Measurement precision
If a Hall Effect sensor is used for current sensing, then measurement accuracy is improved, but cost and circuit complexity increase
Solution Approach 1:
The patent replaces expensive Hall Effect sensors with a simple RC circuit consisting of a sense capacitor and resistor. This inexpensive approach achieves sufficient measurement accuracy for control purposes without requiring complex magnetic field sensing components, thereby reducing both cost and circuit complexity.
Solution Approach 2:
The patent substitutes magnetic field-based sensing (Hall Effect) with an electrical RC circuit approach. By using capacitive coupling and simple voltage division, the system achieves current measurement through electrical means rather than magnetic transduction, simplifying the overall circuit architecture.
3Loss of energy
If a capacitor is connected to a capacitive node for current sensing, then power loss is reduced, but bandwidth and measurement accuracy are limited
Solution Approach 1:
The patent employs a dynamic compensation technique where the sense capacitor value can be adjusted or where multiple capacitors are used in different configurations. This allows the circuit to maintain accurate measurement across varying frequency conditions and load dynamics, overcoming the static limitations of simple capacitive sensing.
Solution Approach 2:
The measured current from the sense capacitor is fed back to the control circuit, which uses this information to adjust switching duty cycles and maintain accurate current regulation. This feedback mechanism compensates for any measurement inaccuracies and extends the effective bandwidth of the sensing system.
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 solution allows for accurate, low-power, and cost-effective current sensing in DC-DC converters, enhancing the dynamic response and reducing power loss, while maintaining stability and accuracy across a wide frequency range.
Implementation Method 1
A second capacitor is coupled to the first capacitor to form a current divider. A second current flows through the second capacitor and is proportional to the first current.
Implementation Method 2
A transimpedance amplifier is coupled to an output of the second capacitor and has a voltage output that is proportional to the second current.
Data Source
Figure 1~3
Figure 4
AI summary
In described examples of a method and circuit for sensing current, a first current (Ir) flows through a first capacitor (108). A second capacitor (220) is coupled to the first capacitor (108) to form a current divider. A second current (Is) flows through the second capacitor (220) and is proportional to the first current (Ir). A transimpedance amplifier (240) is coupled to an output of the second capacitor (220) and has a voltage output (VO) that is proportional to the second current (Is).