Switch Unit Turn-Off Protection for Freewheeling Current Control
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Solution Overview
Problem
In applications with large normal operating currents, such as motor driving and audio amplifier circuits, switching devices face issues with excessive power consumption, overheating, and circuit damage when turned off, due to freewheeling currents flowing through body diodes, leading to undesirable parasitic device conduction and electron/hole injection.
Innovation Solution
A switch unit turn-off protection circuit is implemented, comprising a freewheeling direction detecting circuit and a freewheeling mode regulating circuit, which detects the freewheeling current direction and thresholds to selectively turn on switching devices instead of body diodes, reducing power consumption and preventing overheating by managing freewheeling currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If switching devices are switched from on to off in applications with large normal operating currents, then the switching devices can be turned off to adjust power transmission, but excessive power consumption and overheating occur due to freewheeling currents flowing through body diodes
Solution Approach 1:
The patent introduces an intermediary circuit (freewheeling current redirect circuit) that mediates the path of freewheeling currents. Instead of allowing currents to flow directly through the body diodes of switching devices, the intermediary circuit provides an alternative path using auxiliary switching devices and inductors, thereby reducing power consumption and heat generation in the main switching devices.
Solution Approach 2:
The patent changes the operational parameters of the switching circuit by introducing auxiliary switching devices that can be controlled to change the freewheeling current path. By dynamically adjusting which switching devices are on or off based on current direction and magnitude, the system optimizes power consumption and prevents overheating while maintaining power transmission control.
2Stability of the object's composition
If freewheeling currents are allowed to flow through body diodes of switching devices, then the circuit can maintain current continuity, but parasitic devices may mis-conduct and cause circuit damage due to excessive current
Solution Approach 1:
The patent introduces auxiliary switching devices as intermediaries to control the freewheeling current path. These auxiliary devices prevent excessive currents from flowing through the body diodes of main switching devices, thereby preventing parasitic device mis-conduction and circuit damage while maintaining current continuity through controlled paths.
Solution Approach 2:
The patent implements a control circuit that monitors the state of switching devices and freewheeling current conditions, and provides feedback to adjust the operation of auxiliary switching devices. This feedback mechanism ensures that freewheeling currents are properly managed to maintain current continuity while preventing harmful effects on circuit reliability.
3Device complexity
If body diodes are used for freewheeling in switching devices handling large currents, then the circuit structure remains simple, but overheating and circuit damage occur due to excessive power dissipation
Solution Approach 1:
The patent introduces auxiliary switching devices and inductors as intermediary components to create a controlled freewheeling path. While this increases device complexity slightly, it dramatically reduces power dissipation and overheating by preventing excessive currents from flowing through the body diodes of main switching devices.
Solution Approach 2:
The patent changes the operational parameters by controlling auxiliary switching devices to manage freewheeling current paths dynamically. This parameter control optimizes the balance between circuit complexity and thermal management, reducing overheating while maintaining reasonable circuit structure.
Data Source
AI summary
A turn-off protection circuit and a turn-off protection method for a switch unit. The switch unit may include a first set of switching devices coupled between a first circuit node and an output node, and a second set of switching devices coupled between a second circuit node and the output node. The turn-off protection circuit may compare a first circuit node potential at the first circuit node and/or a second circuit node potential at the second circuit node with a switch node potential at the output node to detect a the flow direction of the a freewheeling current when the switch unit is turned off, and turn on and maintain the first set of switching devices or the second set of switching devices on depending on the flow direction of the freewheeling current until the freewheeling current is reduced to a predetermined safe current threshold.