Current-Sensing Gain Switching Circuit for High-Resolution Power Conversion
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Solution Overview
Problem
Conventional current sensing methods in power factor correction converters face challenges in achieving high resolution while maintaining a small current transformer size, leading to issues with total harmonic distortion and power density, especially at light-load conditions, and existing solutions like shunt resistors or current sensorless control are inefficient or impractical.
Innovation Solution
A current control circuit with a sensor gain switch that selectively connects the primary current to different gain amplifiers, synchronized with controller gain switches, to adjust the current sensing output and prevent core saturation, allowing for high-resolution current measurement with a small current transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large resistance sensing resistor is used in the current transformer secondary side, then current measurement resolution is improved, but the current transformer core saturates and the physical size increases
Solution Approach 1:
The patent applies dynamic gain switching to the current sensing circuit. A gain switch selectively connects different gain amplifiers (first gain amplifier with higher gain, second gain amplifier with lower gain) based on the magnitude of the sensed current. When current is small, the higher gain amplifier is activated to achieve high measurement resolution. When current is large, the lower gain amplifier is activated to prevent core saturation. This dynamic adjustment of gain allows the system to maintain high measurement precision across a wide current range without requiring a large current transformer core.
2Measurement precision
If a large resistance sensing resistor is used, then current measurement resolution is improved, but total harmonic distortion increases at light-load conditions
Solution Approach 1:
The dynamic gain switching mechanism activates the higher gain amplifier specifically during light-load conditions when the sensed current is small. This ensures that the full dynamic range of the ADC is utilized, achieving high current measurement resolution and reducing quantization errors that would otherwise cause high total harmonic distortion. During heavy-load conditions, the lower gain amplifier prevents core saturation while maintaining adequate measurement accuracy.
3Quantity of substance
If a small current transformer is used for high power density, then power density is improved, but current measurement resolution decreases
Solution Approach 1:
The patent enables the use of a small current transformer by dynamically adjusting the gain of the sensing amplifier. The higher gain amplifier compensates for the smaller transformer size by amplifying the weaker signal from the small transformer core, thereby maintaining high measurement resolution despite the reduced transformer size. This allows the system to achieve both high power density and high measurement precision simultaneously.
Solution Approach 2:
The system changes the electrical parameter (gain) of the sensing amplifier based on the operating conditions. By adjusting the gain parameter dynamically, the system optimizes the signal level from the current transformer for the ADC, ensuring high measurement resolution regardless of the transformer size. This parameter adjustment allows small transformers to produce measurement quality comparable to or better than larger transformers without gain adjustment.
4Measurement precision
If gain switching is implemented, then current measurement resolution is improved across wide range, but device complexity increases
Solution Approach 1:
The gain switch serves multiple functions: it selects between different gain amplifiers based on current magnitude, prevents core saturation, and optimizes ADC utilization. The controller integrates the gain switching control logic, combining current sensing, gain selection, and control functions in a unified system. This multi-functionality reduces the need for separate circuits for each function, thereby limiting the increase in overall device complexity.
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 achieves high-resolution current sensing without saturating the current transformer, maintaining power density and efficiency across a wide range of currents, even at light-load conditions, while being cost-effective and practical for implementation.
Implementation Method 1
a current transformer that detects a primary current
Implementation Method 2
a sensor gain switch that selectively connects the primary current to one of a first gain amplifier and a second gain amplifier
Data Source
AI summary
A current control circuit includes a current transformer that detects a primary current, a sensor gain switch that selectively connects the primary current to one of a first gain amplifier and a second gain amplifier to provide a current sensing output, a controller gain switch that selectively connects the current sensing output to one of a first controller amplifier and a second controller amplifier, and a controller that controls switching of the sensor gain switch and the controller gain switch.