Semiconductor Drive Circuit Short Circuit Detection Without Sense Cell
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Solution Overview
Problem
Existing drive circuits for semiconductor elements, such as those described in Japanese Patent Laying-Open No. 2013-123329 and No. 2009-225506, face challenges in determining a short-circuited state without a sense cell and struggle with accurate detection due to small opposite current flow and reliance on specific reference values within a short circuit detection period.
Innovation Solution
A drive circuit comprising a controller, gate voltage detector, gate current detector, signal generation circuit, comparators, and a short circuit determination unit, which generates differential amplification and delay signals to compare with reference values, allowing for easy and high-speed determination of a short-circuited state without requiring a sense cell or shunt resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sense cell and shunt resistor are used to determine short circuit without increasing breakdown voltage, then the drive circuit can determine short circuit state, but the drive circuit cannot be applied to semiconductor elements without sense cell
Solution Approach 1:
The invention extracts the short circuit detection function from the semiconductor element's internal sense cell and implements it externally using only the gate voltage and gate current that are already available at the drive circuit output. This eliminates the requirement for a sense cell while maintaining short circuit detection capability.
Solution Approach 2:
The invention uses gate voltage and gate current as intermediary parameters to indirectly detect the short circuit state of the semiconductor element. Instead of directly measuring collector current or using internal sense cells, the drive circuit monitors the relationship between gate voltage and gate current to determine short circuit conditions.
2Reliability
If gate current detection is used to determine short circuit, then the drive circuit can detect short circuit state, but accurate determination is difficult when opposite current flow is small and detection must occur within short circuit detection period
Solution Approach 1:
The invention changes the detection parameters from absolute gate current values to the relationship between gate voltage and gate current. By monitoring how gate current responds to gate voltage changes and comparing it against expected characteristics, the drive circuit can accurately detect short circuit conditions even when opposite current flow is small or occurs within a brief detection period.
Data Source
AI summary
A drive circuit includes: a signal generation circuit; a comparator; a comparator; and a short circuit determination unit. The signal generation circuit is configured to generate, as an output signal, a differential amplification signal of a voltage detection signal indicating a gate voltage of a semiconductor element and a delay signal of the voltage detection signal. The comparator is configured to compare a value of the differential amplification signal with a first reference voltage value. The comparator is configured to compare a voltage value indicating a gate current with a second reference voltage value. The short circuit determination unit is configured to determine whether or not the semiconductor element is in a short-circuited state, based on a result of comparison by each of the comparators, and generate a determination signal indicating a determination result.