Switch Driving Circuit for Power Steering with Reverse Polarity Protection
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Solution Overview
Problem
Conventional electrically driven power steering systems using relays to control the flow of large currents face challenges with relay size and safety when the battery is connected in reverse polarity, leading to potential short-circuits due to parasitic diodes.
Innovation Solution
A switch driving circuit using two N-channel MOSFETs series connected in opposite directions, with a half-bridge configuration and protection diodes to prevent reverse current flow, ensuring safe operation and reducing the size of the power steering apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a relay is used as a switch to control large current flow, then the switch can reliably open and close the electrical path, but the apparatus size increases due to the large relay required
Solution Approach 1:
The patent replaces the mechanical relay system with a semiconductor-based switch circuit using MOSFETs. This substitution eliminates the need for a large mechanical relay while maintaining the ability to control large currents (several tens A to 100 A) required for motor operation, thereby reducing apparatus size while preserving switch reliability.
Solution Approach 2:
The patent changes the operating parameters of the switching element from mechanical (relay) to semiconductor (MOSFET), enabling the switch to handle large currents with a much smaller physical footprint. The MOSFETs are configured to operate in saturation region for efficient high-current switching, achieving both compact size and reliable performance.
2Volume of moving object
If a switch circuit using N-channel MOSFETs is used instead of a relay, then the apparatus size is reduced, but short-circuits may occur when the battery is connected in reverse polarity due to parasitic diodes
Solution Approach 1:
The patent applies preliminary anti-action by configuring the two N-channel MOSFETs in series with opposite orientations before any fault condition occurs. This configuration, combined with protection diodes, preemptively prevents reverse current flow that would otherwise occur if the battery were connected in reverse polarity, thereby blocking the harmful effect before it can cause a short-circuit.
Solution Approach 2:
The patent introduces protection diodes as intermediary elements between the MOSFETs and the power source. These diodes act as mediators that allow normal current flow in the forward direction while blocking reverse current, thus protecting the MOSFETs from damage due to reverse polarity connection without affecting the compact switch circuit design.
3Reliability
If protection measures are added to prevent reverse polarity damage, then circuit safety is improved, but the device complexity increases
Solution Approach 1:
The patent merges the protection function into the existing switch circuit structure by using the same MOSFETs that control the motor current. The two MOSFETs in series with opposite orientations serve dual purposes: normal motor control and reverse polarity protection. This integration eliminates the need for separate protection circuits, maintaining reliability while minimizing additional complexity.
Solution Approach 2:
The switch circuit achieves multi-functionality where the same components (MOSFETs and protection diodes) perform both the primary function of motor current control and the secondary function of reverse polarity protection. This universal design allows a single circuit to handle multiple functions without proportionally increasing complexity, as the protection features are built into the normal operating structure.
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 short-circuits and reduces the apparatus size by blocking reverse current flow, protecting the inverter circuit and motor while allowing for efficient control of the electrical path.
Implementation Method 1
short-circuits due to parasitic diodes
Data Source
Figure 1
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AI summary
A switch driving circuit electrically opens and closes a switch circuit (5) including two N-channel type semiconductor switching elements (6a, 6b) series connected in opposite directions, thereby electrically opening and closing an electrical path between a DC power supply (4) and an inverter circuit (1). The switch driving circuit (38) has a reference potential point in common with the inverter circuit (1) and supplies an opening/closing control signal to the switch circuit (5). The switch driving circuit (38) includes a half bridge circuit including two semiconductor switching elements (10, 11) series connected between a driving power supply and the reference potential point. Two protection diodes (13, 14) are connected in parallel to the semiconductor switching elements (10, 11) respectively. At least one current blocking diode (39, 42, 43) is configured to block current from flowing from the reference potential point through the diode (39, 42, 43) to the switch circuit (5) side when the DC power supply (4) is connected to the inverter circuit (1) in reverse polarity.