Current Detection Circuit Using Drain-Voltage Division
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Solution Overview
Problem
Current semiconductor devices with normally-on-type switching elements face challenges in accurately detecting output currents due to manufacturing variations in on-resistance, which affect the reliability of current detection.
Innovation Solution
A current detection circuit is designed with a normally-on-type switching element and a normally-off-type switching element in series, along with a division circuit that uses the drain voltages of both elements to accurately detect output currents by canceling out variations in on-resistance through a specific dimension ratio and constant current source configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a normally-on-type switching element is used in a semiconductor device, then high voltage resistance and low loss are achieved, but accurate detection of output current becomes impossible 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 can be completely turned off to block leakage current, while still allowing the output current to be measured through its source terminal, thus resolving the conflict between maintaining low loss operation and achieving accurate current detection.
2Strength
If a normally-on-type switching element is used, then high voltage resistance is achieved, but manufacturing variations cause characteristic variations such as on-resistance
Solution Approach 1:
The invention changes the operational parameters of the switching elements by using a normally-off-type switching element whose on-resistance can be precisely controlled and matched to the normally-on-type switching element. This parameter matching approach compensates for manufacturing variations and enables accurate current detection despite variations in individual device characteristics.
3Measurement precision
If current detection is implemented in a semiconductor device with normally-on-type switching elements, then output current monitoring is achieved, but reliability is reduced due to leakage current and manufacturing variations
Solution Approach 1:
The invention implements a feedback mechanism where the current detection circuit monitors the output current through the normally-off-type switching element and provides this information to the control circuit. The control circuit can then adjust the gate voltage of the normally-on-type switching element to maintain reliable operation, compensating for leakage current effects and manufacturing variations through continuous feedback control.
Data Source
AI summary
A current detection circuit includes normally-on-type and a first normally-off-type switching elements with main current paths that are connected in series, and a second normally-off-type switching element that has a source and a gate that are connected to a source and a gate of the first normally-off-type switching element and a drain that is connected to a constant current source, and executes a division process by using drain voltages of the two normally-off-type switching elements.