Cascode Current Sensing Circuit for Leakage-Accurate Detection
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Solution Overview
Problem
Conventional current detecting circuits for semiconductor devices with normally-ON type switching elements, such as those made from GaN and SiC, face challenges in precisely detecting output current due to leakage currents, leading to unreliable current measurement.
Innovation Solution
A current detecting circuit is designed with a normally-ON type switching element and a normally-OFF type switching element in cascode connection, along with a differential amplification circuit that outputs a voltage proportional to the drain-source voltage of the normally-OFF type switching element, allowing precise detection of output current by operating the normally-OFF type switching element in a linear region and using an adjustment circuit to prevent overvoltage and improve reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a normally-ON type switching element is used to achieve high withstand voltage and low energy loss, then the energy efficiency and voltage capability are improved, but the output current detection precision deteriorates due to leakage current
Solution Approach 1:
A normally-OFF type switching element is introduced as an intermediary component between the normally-ON type switching element and the current detection circuit. This intermediary element blocks leakage current from reaching the detection circuit while allowing controlled current to pass through during normal operation, thereby enabling accurate current detection without sacrificing the low energy loss benefits of the normally-ON type switching element
Solution Approach 2:
The switching function is segmented into two distinct elements: a normally-ON type switching element for high voltage blocking and low conduction loss, and a normally-OFF type switching element for precise current control and leakage blocking. This segmentation allows each element to optimize its specific function, with the normally-OFF element dedicated to current detection accuracy by eliminating leakage current interference
2Measurement precision
If a current detecting circuit is designed to precisely detect output current, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The normally-OFF type switching element serves multiple functions simultaneously: it acts as a leakage current block, a controlled current path during operation, and an integral part of the current detection mechanism. This multi-functionality eliminates the need for separate leakage blocking components and simplifies the overall circuit architecture while maintaining high detection precision
Solution Approach 2:
The current detection function is merged with the switching element structure itself. The drain-source voltage of the normally-OFF type switching element directly reflects the output current, combining the switching operation and current sensing into a single integrated component rather than requiring separate sensing circuits
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 enables precise detection of output current while preventing erroneous overcurrent detection and reducing power consumption, enhancing the reliability and simplicity of the semiconductor device's current detecting circuit.
Implementation Method 1
a differential amplification circuit that outputs a voltage according to a voltage between the drain and the source of the second switching element
Data Source
AI summary
According to one embodiment, a current detecting circuit includes: a normally-ON type first switching element that includes a drain, a source, and a gate; a normally-OFF type second switching element including a drain that is connected to the source of the first switching element, a source that is connected to the gate of the first switching element, and a gate; and a differential amplification circuit that outputs a voltage according to a voltage between the drain and the source of the second switching element.