Load Drive Device Dual Pre-Driver Overcurrent Protection
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Solution Overview
Problem
Existing load drive devices face issues with switching loss during normal operation and overcurrent protection, leading to potential damage of the output transistor due to rapid switching and excessive counter voltages generated during overcurrent protection operations.
Innovation Solution
A load drive device with a pre-driver that has a first drive unit for normal operation switching and a second drive unit for slower switching during overcurrent protection, along with an overcurrent protection circuit and a mask time generation circuit to manage the output transistor's switching, reducing switching loss and protecting the transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output transistor is rapidly switched on/off during normal operation, then switching speed is improved, but switching loss increases
Solution Approach 1:
The pre-driver dynamically changes its driving characteristics based on operating conditions. During normal operation, it provides rapid switching with strong drive capability. During overcurrent protection, it transitions to a softer switching mode with reduced drive strength, preventing excessive counter voltage while still achieving protection function.
Solution Approach 2:
The invention changes the driving parameters of the output transistor by using a dual-structure pre-driver with different drive capabilities. The first drive unit provides high-speed switching parameters during normal operation, while the second drive unit provides controlled, slower switching parameters during overcurrent protection to reduce voltage spikes.
2Reliability
If the output transistor is rapidly switched off during overcurrent protection, then protection response is improved, but excessive counter voltage damages the transistor
Solution Approach 1:
The mask time generation circuit activates the second drive unit in advance before the overcurrent protection fully kicks in. This preliminary action prepares the output transistor for a controlled shutdown, preventing the generation of excessive counter voltage that would otherwise damage the transistor during rapid cutoff.
Solution Approach 2:
The second drive unit acts as an intermediary between the overcurrent protection signal and the output transistor. It mediates the shutdown process by providing a controlled, gradual gate voltage reduction instead of an abrupt cutoff, thereby preventing excessive counter voltage while still achieving protection.
3Device complexity
If a single pre-driver is used for both normal operation and overcurrent protection, then device complexity is reduced, but switching performance deteriorates
Solution Approach 1:
The pre-driver is segmented into two distinct drive units: a first drive unit for normal operation providing rapid switching, and a second drive unit for overcurrent protection providing controlled shutdown. This segmentation allows each unit to be optimized for its specific function, maintaining high switching performance while adding protection capability.
Solution Approach 2:
The pre-driver achieves multi-functionality by combining two drive units that can operate in different modes. The first drive unit handles normal high-speed switching, while the second drive unit handles protection scenarios. Together, they provide a universal pre-driver structure that handles both normal operation and abnormal protection conditions effectively.
Data Source
AI summary
The load drive device of the present invention comprises a load drive unit for switching on/off output current that flows to an inductive load; and an overcurrent protection circuit for detecting whether the output current is in an overcurrent state, wherein the load drive unit has an output transistor connected to one end of the inductive load; and a pre-driver for generating a control signal of the output transistor in accordance with an input signal, and the pre-driver has a first drive unit for switching on/off the output transistor during normal operation; and a second drive unit for switching off the output transistor more slowly than the first drive unit during overcurrent protection operation.