DC/DC Converter Soft Stop Control for Overvoltage Prevention
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Solution Overview
Problem
DC/DC converters face challenges in preventing overvoltage and overcurrent during stop operations, leading to inefficiencies and potential damage, particularly due to parasitic capacitance and ON resistance issues in self-driving systems.
Innovation Solution
The implementation of a DC/DC converter design that includes a transformer, main and auxiliary MOS transistors, synchronous rectification MOS transistors, and a refluxing MOS transistor, controlled by a controller to manage input and output currents, employing soft stop operations and ON-ON overlap times to alleviate dead time and prevent overvoltage and overcurrent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a self-driving system is used in the DC/DC converter, then the device complexity is reduced, but overvoltage and overcurrent occur during stop operations due to parasitic capacitance and ON resistance
Solution Approach 1:
The patent introduces a controller as an intermediary between the primary and secondary sides to manage the stop operation sequence. The controller coordinates the shutdown of the main MOS transistor, synchronous rectification MOS transistor, and refluxing MOS transistor, preventing overvoltage and overcurrent by ensuring proper timing and sequence of transistor shutdown, thus resolving the reliability issue while maintaining controlled complexity
Solution Approach 2:
The patent applies preliminary action by stopping the main MOS transistor before stopping the synchronous rectification MOS transistor and refluxing MOS transistor during shutdown. This pre-planned sequence of operations prevents overvoltage and overcurrent from occurring in the first place, addressing the reliability concern through proactive control
2Loss of energy
If dead time is reduced in the switching operation, then the power conversion efficiency is improved, but overvoltage occurs in the drains of synchronous rectification MOS transistor and refluxing MOS transistor
Solution Approach 1:
The patent applies dynamics by making the dead time adjustable rather than fixed. The controller dynamically adjusts the dead time between switching operations based on operating conditions, allowing the system to optimize efficiency when possible while preventing overvoltage when necessary, thus resolving the contradiction between efficiency and overvoltage prevention
Solution Approach 2:
The patent changes the parameter of dead time based on operating conditions. By varying the dead time duration, the system can achieve high efficiency during normal operation while preventing overvoltage conditions during transient states or shutdown, addressing both the efficiency improvement and overvoltage prevention requirements
3Ease of operation
If the synchronous rectification MOS transistor and refluxing MOS transistor are stopped simultaneously with the main MOS transistor, then the stop operation is simplified, but overcurrent occurs in the refluxing MOS transistor
Solution Approach 1:
The patent applies preliminary action by stopping the main MOS transistor before stopping the synchronous rectification MOS transistor and refluxing MOS transistor. This pre-planned sequence prevents overcurrent in the refluxing MOS transistor by ensuring that energy has already been dissipated or redirected before the reflux path is closed, thus preventing harmful overcurrent while maintaining relatively simple control logic
Data Source
AI summary
A DC/DC converter includes: a transformer; a main MOS transistor connected in series between a primary side inductance of the transformer and a ground potential; a synchronous rectification MOS transistor connected in series between a secondary side inductance of the transformer and the ground potential; a refluxing MOS transistor connected between a secondary side output of the transformer and the ground potential; and a controller. If an operation is stopped, the controller stops the main MOS transistor and stops the synchronous rectification MOS transistor and the refluxing MOS transistor after a lapse of a predetermined period of time.