Overcurrent Detection Circuit With Built-In Temperature Compensation
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Solution Overview
Problem
Existing current sensors in power semiconductor switches like IGBTs and MOSFETs are temperature-dependent, leading to inaccurate over-current detection and increased complexity and cost due to the need for correction circuits and temperature sensors.
Innovation Solution
A temperature-independent overcurrent detection circuit is implemented using a built-in temperature-sensitive element, such as a gate resistor or diodes, coupled with a current sensor to compensate for temperature variations, allowing precise over-current detection without additional sensors or complex correction circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a built-in current sensor is used to detect over-current, then the detection is compact and reliable, but the sensor sensitivity becomes dependent on junction temperature leading to inaccurate detection
Solution Approach 1:
The patent changes the operating parameters by introducing a dedicated measurement period during which the semiconductor switch is temporarily switched off. This allows the current sensor to operate under controlled conditions (zero collector current) where temperature compensation can be applied, transforming the sensor's temperature-dependent behavior into a predictable and compensatable characteristic.
Solution Approach 2:
The patent performs preliminary temperature compensation measurements during a dedicated period before normal operation. By measuring the sensor output when collector current is zero and calculating compensation values in advance, the system prepares correction data that will be applied during actual over-current detection, ensuring accurate measurements despite temperature variations.
2Measurement precision
If correction circuits and temperature sensors are added to compensate for temperature dependency, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the system self-sufficient by using its own internal resources for temperature compensation. The dedicated measurement period utilizes the existing current sensor and switch structure without requiring external temperature sensors or complex correction circuits. The system compensates for its own temperature effects using built-in capabilities, eliminating the need for additional components.
Solution Approach 2:
The patent implements periodic measurement cycles where the switch is temporarily turned off to perform temperature compensation measurements. This periodic action allows the system to refresh compensation data at regular intervals, maintaining measurement accuracy throughout operation without requiring continuous complex correction circuits. The periodic nature simplifies the circuit design compared to continuous compensation approaches.
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 provides accurate over-current detection independent of junction temperature, reducing complexity and cost while maintaining high sensitivity and reliability.
Implementation Method 1
a temperature sensitive element, such as a gate resistor or diodes, coupled with a current sensor to compensate for temperature variations
Data Source
Figure 1
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AI summary
Overcurrent detection circuit for a semiconductor switch (10) such as an IGBT or a MOSFET said detection circuit comprising a compensation circuit configured to at least partly compensate a temperature dependency of a built-in current mirror (12) output of said power semiconductor switch (10), said current mirror output (12) being connected to a measurement resistor Rs (20, 20'), connected between said current mirror output and a low voltage level of a driver voltage source (40), and connected to a first adder input having a second adder input receiving an offset Vofst (32) to provide a mirror voltage Vs mirroring the current Ic flowing through the power switch emitter-collector or drain-source junction. The compensation circuit comprises a current source (31) configured to provide a reference current iR and connected to a temperature sensitive element (13, 14) of said power semiconductor switch in which said reference current iR flows during at least a dedicated period of measurement through said temperature sensitive element (13, 14) to provide a reference voltage Ve, a comparator (34, 34'), comparing said reference voltage Ve or an amplified reference voltage βVd and said mirror voltage and said compensation circuit is configured to provide at an output of said comparator a detection signal Ocd changing its state when said mirror voltage exceeds said reference voltage Ve or said amplified reference voltage βVd.