Motor Relay Gate Cutoff for MOSFET Short-Circuit Detection
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Solution Overview
Problem
Conventional motor driving devices face challenges in reliably detecting short-circuit abnormalities in N-channel MOSFETs, particularly due to the difficulty in fully disconnecting the MOSFETs and distinguishing between normal and abnormal voltage levels, which affects the accuracy of abnormality detection and safe operation of the motor system.
Innovation Solution
The implementation of a power relay control unit with gate cutoff relays and a control unit that shares gate control lines with motor relays, allowing for effective turning on and off of the power relay, ensuring the MOSFETs are fully turned off and enabling accurate abnormality detection by creating a clear voltage difference for comparator analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If N-channel MOSFETs are used in the power relay, then the switching speed and efficiency are improved, but the reliability of short-circuit abnormality detection deteriorates due to difficulty in fully disconnecting the MOSFETs
Solution Approach 1:
A gate cutoff relay is introduced as an intermediary component between the control unit and the N-channel MOSFET gate. This relay includes a P-channel MOSFET that can fully disconnect the gate voltage, ensuring complete turn-off of the N-channel MOSFET. The gate cutoff relay acts as a mediator that overcomes the limitation of N-channel MOSFETs not being able to fully disconnect, thereby enabling reliable short-circuit abnormality detection while maintaining the switching speed benefits of N-channel MOSFETs.
2Device complexity
If the gate control line is shared between motor relays and power relay control unit, then the device complexity is reduced, but the measurement precision of voltage difference for abnormality detection deteriorates
Solution Approach 1:
The gate control function is segmented into two distinct parts: the motor relay control and the power relay control unit. Although they share a common gate control line, the power relay control unit includes a dedicated gate cutoff relay that can independently control the power relay MOSFET gate voltage. This segmentation allows the system to maintain low complexity through line sharing while ensuring detection precision through independent voltage control capability when abnormality detection is required.
3Measurement precision
If the power relay is fully turned off for abnormality detection, then the detection accuracy is improved, but the operational time and response speed deteriorate due to complete disconnection
Solution Approach 1:
The gate cutoff relay is activated periodically or on-demand to fully turn off the power relay MOSFET for short-circuit abnormality detection, rather than maintaining continuous disconnection. This periodic action allows the system to achieve high detection accuracy when needed while minimizing the loss of operational time. The control unit can quickly reactivate the MOSFET after detection, ensuring that the complete disconnection duration is minimized and does not significantly impact overall system response time.
Data Source
AI summary
The present disclosure provides a motor driving device. The motor driving device includes a control unit operable to output gate signals to gates of motor relays. The gate signals are inputted to a power relay control unit operable to switch whether to apply an output voltage to a gate of the power relay.