Current Detecting Circuit Leakage Compensation GaN
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Solution Overview
Problem
Conventional current detecting circuits using normally-ON switching elements, such as those made from GaN or SiC, face challenges in precisely detecting output currents due to leakage currents, which affects the reliability and accuracy of current detection in power source circuits, especially in applications like AC/DC converters.
Innovation Solution
A current detecting circuit is designed with a normally-ON type switching element and two normally-OFF type switching elements, where the drain voltages of these elements are compared using a comparison circuit to generate a detection signal, allowing for precise detection of output currents by controlling the reference current and adjusting the ON resistances of the switching elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a normally-ON switching element is used in a power source circuit, then high withstand voltage and low loss are achieved, but output current detection precision deteriorates due to leakage current
Solution Approach 1:
The patent segments the current detection function by separating the normally-ON switching element (which handles high voltage and generates leakage current) from the detection circuit. A normally-OFF switching element is introduced to create a dedicated detection path that is electrically isolated from the leakage current of the main power path, enabling precise current measurement without interference.
Solution Approach 2:
The normally-OFF switching element acts as an intermediary between the high-voltage power path and the low-voltage detection circuit. It transfers a proportional current from the main power path to the detection circuit while blocking the harmful leakage current, thus mediating between the conflicting requirements of high power efficiency and precise measurement.
2Reliability
If a normally-ON switching element is used to achieve high withstand voltage, then reliability for high-voltage applications is improved, but current detection accuracy deteriorates
Solution Approach 1:
The circuit is segmented into a high-voltage power path using the normally-ON switching element for reliable high-voltage operation, and a separate low-voltage detection path using the normally-OFF switching element for accurate current measurement. This segmentation allows each part to optimize its function without compromising the other.
Solution Approach 2:
The detection function is extracted from the main power path by introducing a separate detection branch with the normally-OFF switching element. This extracted detection path operates independently from the high-voltage power path, eliminating the interference of leakage current while maintaining the reliability benefits of the normally-ON switching element.
3Power
If leakage current from normally-ON switching element is present, then high-voltage power conversion is enabled, but phase matching for power factor improvement becomes inaccurate
Solution Approach 1:
The normally-OFF switching element serves as an intermediary that creates a clean detection path for measuring the actual output current phase. By blocking the leakage current while allowing proportional current transfer, it enables accurate phase detection necessary for power factor correction in high-voltage AC/DC converters.
Solution Approach 2:
The patent replaces the direct electrical connection method (which is contaminated by leakage current) with a controlled current transfer mechanism using the normally-OFF switching element. This substitution creates a clean signal path for phase detection, enabling accurate power factor correction control.
Data Source
AI summary
According to an embodiment, a current detecting circuit includes: a normally-OFF type second switching element that is cascode-connected to a normally-ON type first switching element that includes a drain for outputting an output current; a normally-OFF type third switching element that is connected in parallel to the second switching element and whose drain is connected to a variable current source; and a comparison circuit that outputs a detection signal in accordance with a comparison result between a drain voltage of the second switching element and a drain voltage of the third switching element.