Non-isolated DC-DC Converter Dual-Stage Overvoltage Protection
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Solution Overview
Problem
Non-isolated DC-DC voltage converters lack effective overvoltage protection mechanisms, particularly in scenarios where a shorted switching element can cause the input voltage to be directly applied to the output, potentially damaging critical loads and violating certification requirements.
Innovation Solution
A dual-stage overvoltage protection scheme is implemented, comprising an external overvoltage comparator circuit and a current-limited power disconnect MOSFET for the first stage, and a fast-responding synchronous buck regulator controller for the second stage, which limits peak voltage and current during faults, ensuring safe operation and automatic recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a non-isolated DC-DC converter is used to reduce cost and complexity, then device complexity and cost are reduced, but overvoltage protection capability deteriorates
Solution Approach 1:
The protection system is divided into two independent stages: an external protection stage with overvoltage comparator and power disconnect MOSFET, and an internal protection stage with synchronous buck regulator controller. This segmentation allows each stage to handle specific protection functions, achieving comprehensive overvoltage protection without requiring a complex isolated transformer structure.
Solution Approach 2:
The power disconnect MOSFET acts as an intermediary component between the input voltage source and the converter circuit. It is controlled by the overvoltage comparator to disconnect input power when overvoltage conditions are detected, providing protection without requiring direct isolation between input and output.
2Speed
If a fast-responding protection scheme is implemented, then overvoltage response speed is improved, but power dissipation increases
Solution Approach 1:
The external overvoltage protection stage operates periodically by detecting overvoltage conditions, activating the power disconnect MOSFET to remove input power, and allowing automatic recovery when the fault condition is removed. This periodic action provides fast protection response while minimizing continuous power dissipation during normal operation.
Solution Approach 2:
The overvoltage comparator continuously monitors the output voltage and prepares to activate the power disconnect MOSFET before damage occurs. By taking preliminary protective action at the external stage, the system prevents the need for continuous high-power dissipation protection mechanisms.
3Reliability
If the bottom synchronous MOSFET is protected during fault conditions, then component reliability is improved, but current limiting capability may be restricted
Solution Approach 1:
The power disconnect MOSFET is sized and configured to provide beforehand cushioning by limiting the maximum current that can flow during fault conditions. This pre-configured current limitation protects the bottom synchronous MOSFET from exceeding its safe operating area without requiring additional complex current limiting circuitry.
Data Source
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AI summary
A non-isolated (transformerless) direct current-to-direct current (DC-DC) power supply includes a voltage converter module that converts DC input voltage having a first voltage level into a DC output having a second voltage level that is less than the first voltage level. An overvoltage protection module (125) interposed between the input voltage source and the input to the DC-DC converter monitors the DC output and removes power from the voltage converter module if the DC output exceeds an overvoltage threshold. A second level of overvoltage protection (130) that responds faster than the power disconnect module is provided within the DC-DC converter PWM controller, providing additional overvoltage protection to the DC-DC converter and preventing application of the input voltage to the converter output.