FET Overcurrent Protection via Drain-Source Voltage Rate Detection
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Solution Overview
Problem
Conventional overcurrent protection power supply apparatuses are inadequate for high voltage DC power sources, as they fail to effectively protect MOSFETs from excessive currents and heat generated due to electromagnetic energy accumulation, leading to potential damage during ground faults in electric vehicles or hybrid vehicles.
Innovation Solution
An overcurrent protection power supply apparatus using a Field Effect Transistor (FET) with a control circuit that detects drain-source voltage and its increasing rate to initiate overcurrent protection, ensuring timely shutdown and preventing FET damage, even at high voltage DC power sources like 500V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional overcurrent protection power supply apparatus is used with high voltage DC power source, then the apparatus can supply power to load, but the MOSFET cannot protect against excessive current and heat during ground faults
Solution Approach 1:
The protection circuit performs preliminary detection of drain-source voltage and its increasing rate to predict overcurrent conditions before they occur. By monitoring the rate of change (dVds/dt), the circuit can initiate protection actions in advance, turning off the MOSFET before excessive current and heat damage occur during ground faults.
Solution Approach 2:
The protection circuit continuously monitors the drain-source voltage and feeds back the increasing rate information to the control circuit. This feedback mechanism enables real-time adjustment of the MOSFET gate voltage, allowing the system to respond dynamically to changing conditions and prevent overcurrent damage.
2Reliability
If the protection operating time is reduced for high voltage systems, then the MOSFET can be protected from overcurrent, but the detection and response speed must be increased
Solution Approach 1:
The invention replaces conventional current-based detection methods with voltage-based detection. By monitoring drain-source voltage and its rate of change instead of directly measuring current, the system achieves faster detection response. The voltage signal changes more rapidly than current, enabling the protection circuit to react faster to ground fault conditions.
Solution Approach 2:
The protection circuit changes the detection parameter from current magnitude to voltage increasing rate (dVds/dt). This parameter transformation allows the system to detect overcurrent conditions faster, as the voltage across the MOSFET changes more rapidly during ground faults than the current itself, reducing the protection operating time required.
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 effectively prevents major overcurrents and heat-related damage to FETs, allowing their safe use in high voltage DC power systems by accurately detecting and responding to voltage and current changes during ground faults.
Implementation Method 1
a drain-source voltage generated between a drain and a source of the FET by flowing of a drain current through the FET
Data Source
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AI summary
An object of the present invention is to inexpensively and surely protect a FET against an overcurrent, via which electric power is supplied from a high-voltage DC power source to a load. Electric power is supplied from a high-voltage DC power source 63 to a load 66 via a FET 60. A drain-source voltage detecting circuit 2 detects a drain-source voltage VDS of the FET 60. A first overcurrent protection signal generating circuit 7 outputs a first overcurrent protection signal based on the drain-source voltage VDS of the FET 60. A second overcurrent protection signal generating circuit 8 outputs a second overcurrent protection signal based on a gradient increase (increasing rate) of the drain-source voltage VDS of the FET 60. A control circuit 16 turns off the FET 60 to protect the FET 60 against an overcurrent when the first overcurrent protection signal is output from the first overcurrent protection signal generating circuit 7 or the second overcurrent protection signal is output from the second overcurrent protection signal generating circuit 8.