Capacitive Current Sensor Circuit for Low-Loss Power Converters
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Solution Overview
Problem
Conventional current sensors in power converters waste significant power, which is a concern for high-efficiency converters.
Innovation Solution
A low-loss current sensor using a capacitive current divider and a differentiator circuit with a sensing capacitor and resistor, allowing for current sensing with virtually zero energy dissipation, integrated into a power converter with dynamically controlled switches for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional current sensor using a shunt resistor is used to measure current, then current measurement is achieved, but significant power is wasted
Solution Approach 1:
The patent introduces a capacitor as an intermediary element to sense current indirectly. Instead of measuring current directly through a resistive shunt, the capacitor senses the voltage across it which is proportional to the current flowing into the node. This intermediary approach allows current measurement without the continuous power dissipation of a shunt resistor.
Solution Approach 2:
The patent replaces the conventional resistive current sensing mechanism with a capacitive sensing mechanism combined with a differentiator circuit. The differentiator circuit processes the capacitive voltage signal to produce a current-proportional output, substituting the mechanical/electrical resistive measurement approach with an electronic differentiation approach that consumes minimal power.
2Loss of energy
If AC currents are minimized to maintain high efficiency, then power wastage is reduced, but current sensing capability must be maintained
Solution Approach 1:
The patent utilizes the periodic nature of switching operations in power converters. The differentiator circuit is configured to process signals during specific switching intervals, extracting current information during dead times when AC currents are naturally minimized. This periodic sampling approach maintains measurement capability while operating during low-power-loss intervals.
Solution Approach 2:
The patent makes the existing circuit capacitances (such as MOSFET output capacitances) serve dual purposes: they function as part of the power conversion process and simultaneously serve as the sensing element for current measurement. This self-service approach eliminates the need for separate high-power sensing components.
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 power wastage, maintaining high efficiency across varying load conditions, including at light loads, by minimizing AC currents and optimizing switch timings and dead times.
Implementation Method 1
a differentiator circuit having an input connected to the circuit capacitor and adapted to generate an output signal, which is proportional to the current flowing into the circuit capacitor
Implementation Method 2
a differentiator circuit having an input connected to the circuit capacitor and adapted to generate an output signal, which is proportional to the current flowing into the circuit capacitor
Data Source
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AI summary
A low-loss current sensor for use with a circuit containing a capacitor to sense a current flowing into a node in the circuit is provided. The current sensor includes a differentiator circuit having an input connected to the circuit capacitor and adapted to generate an output which is proportional to the current flowing through the circuit capacitor. The novel use of a capacitive current divider allows the sensor to sense current with virtually no power dissipation.