Cross-Coupled Current Sense Circuit for Low-Load Accuracy
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Solution Overview
Problem
Current power switching apparatuses face limitations in achieving accurate current sense, particularly at low load currents due to error amplifier offset, which affects the reliability and efficiency of smart power switching circuits in diverse load applications.
Innovation Solution
The implementation of a power switching circuit arrangement that includes a cross-coupling switching module to switch between modes, allowing the offset introduced by the error amplifier to be either added or subtracted from the current sense feedback, enabling offset compensation by averaging measurements taken in different modes, thereby improving current sense accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If error amplifier offset is present in current sense feedback, then the circuit can operate with simple structure, but current sense accuracy deteriorates at low load currents
Solution Approach 1:
The patent applies periodic action by switching the error amplifier between two modes (first mode and second mode) at different times. In the first mode, the error amplifier provides normal current sense feedback with its offset. In the second mode, the error amplifier is reconfigured to provide feedback with opposite polarity, effectively reversing the offset. By periodically alternating between these two modes and averaging the measurements, the offset component cancels out while the actual current signal remains, thereby improving current sense accuracy without requiring a completely different circuit architecture.
2Measurement precision
If offset compensation techniques are applied, then current sense accuracy improves, but device complexity increases
Solution Approach 1:
The patent utilizes feedback by taking measurements in both modes and computing an average value. The feedback mechanism involves using the measured current sense signals from both modes to calculate the compensated current value. By feeding back the averaged result, the system achieves offset compensation while maintaining a relatively simple circuit structure that leverages the existing error amplifier and control logic.
3Measurement precision
If two points calibration is used, then current sense accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements self-service by enabling the power switching apparatus to perform its own offset compensation internally through mode switching and averaging. The system automatically compensates for its own error without requiring external calibration equipment or complex manufacturing processes. This self-compensating mechanism reduces manufacturing complexity and cost while maintaining high current sense accuracy across different production units.
Data Source
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AI summary
A power switching apparatus (70) comprises a power switching circuit arrangement (30, 72) comprising an input (32) connectable to a power supply, a first output (34) connectable to a load, a second output (36) arranged to provide a sense current depending on a load current flowing through the load, a power switching device (38), a sense device (40), and a difference amplification device (42), which comprises a first (44) and a second (46) amplifier input, at least one amplifier output (48) connected to a current sense feedback loop (50, 52, 54) arranged to reduce a difference of potentials between the first and the second amplifier input. A first terminal of the power switching device and a first terminal of the sense device are connected to the input and a second terminal (56) of the power switching device and a second terminal (58) of the sense device are coupled to a first cross-coupling switching module (60). The module is arranged to connect, depending on a mode signal, in a first mode the second terminal of the power switching device to the first input of the difference amplification device and the second terminal of the sense device to the second input of the difference amplification device and in a second mode the second terminal of the power switching device to the second input of the difference amplification device and the second terminal of the sense device to the first input of the difference amplification device.