MOSFET Ground Bypass Circuit for Motor Control Protection
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Solution Overview
Problem
Existing electric motor systems face damage due to ground disconnection events, where large currents from the power circuitry flow through the control circuitry, exceeding its capacity, leading to destruction, especially in applications where high reliability and safety are critical.
Innovation Solution
A circuit with power MOSFETs in a common-source arrangement is configured to bypass current between two grounds during a ground disconnection event, protecting the control circuitry by activating when a voltage differential exceeds a threshold, using low-power components to extend the common mode range without the need for expensive high-power diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground disconnection protection is implemented using traditional high-power diodes, then the control circuitry is protected from large currents, but the cost and device complexity increase significantly
Solution Approach 1:
The patent changes the electrical parameters of the protection circuit by using power MOSFETs with specific threshold voltages that allow them to operate in a linear region during ground disconnection events. This enables the MOSFETs to handle high currents while maintaining a controlled voltage drop, replacing the need for expensive high-power diodes with lower-cost MOSFETs that can be operated in their linear region.
Solution Approach 2:
The patent introduces an intermediary protection circuit composed of power MOSFETs configured in a common-source arrangement between the power ground and control ground. This intermediary circuit activates during ground disconnection events to provide a safe current path, mediating between the high-current power circuitry and the sensitive control circuitry without requiring direct connection or expensive protective components.
2Reliability
If high-power diodes are used for ground protection, then current bypass capability is achieved, but the cost increases
Solution Approach 1:
The patent employs power MOSFETs that are generally less expensive than high-power diodes capable of handling the same current levels. The MOSFETs are configured to operate in their linear region during protection events, allowing them to function as disposable protective elements that can be replaced if needed, rather than requiring expensive high-power diodes with high reverse voltage ratings.
Solution Approach 2:
The patent changes the operational parameters by biasing the power MOSFETs to operate in their linear region rather than saturation region, allowing them to function as variable resistors during ground disconnection events. This parameter change enables the use of lower-cost MOSFETs instead of expensive high-power diodes while maintaining the necessary current handling capability.
3Adaptability or versatility
If the common mode range is extended using traditional methods, then the voltage differential tolerance increases, but the device complexity and cost increase
Solution Approach 1:
The patent makes the power MOSFETs perform multiple functions: they serve as both the main switching elements in the half-bridge topology and as the ground protection elements simultaneously. The same MOSFETs that control motor phase currents also provide ground disconnection protection when configured in the common-source arrangement, eliminating the need for separate protection components and extending the common mode range without additional complexity.
Solution Approach 2:
The patent merges the ground protection function with the existing power MOSFETs in the half-bridge topology. By configuring the MOSFETs in a common-source arrangement between the two grounds, the invention combines the current handling capability of the power MOSFETs with the ground protection function, thereby extending the common mode range without adding separate protection circuits or components.
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
This solution effectively protects the control circuitry from large currents during ground disconnection events, providing a wider common mode range while maintaining isolation and reducing the risk of damage, especially in automotive and safety applications, using low-cost, low-power components.
Implementation Method 1
configured to turn on during a ground disconnection event in an electric motor system, allowing a current to pass between the first ground and the second ground, the current bypassing a control circuit
Data Source
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AI summary
In a circuit for ground disconnection protection, the circuit includes power transistor elements in a common-source arrangement (511, 512) coupled between a first ground (272) and a second ground (274). The power transistor elements (511, 512) are configured to turn on during a ground disconnection event (310) in an electric motor system. This allows a current (530) to pass between the first ground (272) and the second ground (274), bypassing a control circuit (210).