Synchronous Rectifier Overvoltage Protection via Current Shunting
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Solution Overview
Problem
Synchronous rectifiers face damage from unintended overvoltage conditions due to parasitic body diodes, which can lead to excessive DC voltage output when switched off, and existing solutions like voltage clamps increase system complexity and cost with additional components.
Innovation Solution
A control unit monitors the DC output voltage and adjusts the operational state of the rectifier's switches to prevent overvoltage by shunting current away from the AC input, eliminating the need for external components like high-voltage capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage clamps (high-voltage capacitors) are used to protect the synchronous rectifier from overvoltage conditions, then the rectifier is protected from damage, but the system complexity and cost increase due to additional external components
Solution Approach 1:
The patent extracts the overvoltage protection function from external voltage clamps and relocates it to the synchronous rectifier's own control unit. The control unit monitors DC output voltage and selectively activates low-side switches to shunt excess current, eliminating the need for external high-voltage capacitors and reducing system complexity while maintaining protection reliability
Solution Approach 2:
The synchronous rectifier performs its own overvoltage protection through the control unit that monitors DC output voltage and activates protection mode by shunting current through low-side switches when overvoltage is detected. This self-service approach eliminates dependency on external protection components and reduces overall system complexity
2Reliability
If voltage clamps (high-voltage capacitors) are used to protect the synchronous rectifier from overvoltage conditions, then the rectifier is protected from damage, but the system cost increases due to additional external components
Solution Approach 1:
The patent extracts the overvoltage protection function from external voltage clamps and relocates it to the synchronous rectifier's own control unit. The control unit monitors DC output voltage and selectively activates low-side switches to shunt excess current, eliminating the need for external high-voltage capacitors and reducing system complexity while maintaining protection reliability
Solution Approach 2:
The control unit is designed to perform multiple functions: normal rectification control and overvoltage protection. By making the control unit universal, the patent eliminates the need for separate external protection components, thereby reducing system cost and simplifying manufacturing
3Ease of operation
If the synchronous rectifier operates with parasitic body diodes acting as passive elements, then the rectifier can function without active control, but the rectifier becomes vulnerable to overvoltage damage from large AC voltage inputs
Solution Approach 1:
The patent implements dynamic switching control where the control unit actively manages the state of MOS switches based on operating conditions. During normal operation, switches are controlled for efficient synchronous rectification; during overvoltage conditions, the control unit activates protection mode by switching low-side devices to shunt current, providing adaptive protection while maintaining ease of operation
Solution Approach 2:
The control unit continuously monitors the DC output voltage and uses this feedback to determine when to activate protection mode. When the monitored voltage exceeds safe thresholds, the control unit responds by activating low-side switches to shunt current, thereby preventing overvoltage damage while allowing passive-like operation under normal conditions
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
This approach effectively protects synchronous rectifiers from overvoltage without external components, reducing system size and cost while maintaining efficient rectification.
Implementation Method 1
a sensing unit configured to detect a voltage level of the DC output
Implementation Method 2
shunt current from the AC input if the voltage level of the DC output does indicate the overvoltage condition
Implementation Method 3
a rectifier configured to rectify a DC output from an AC input
Data Source
AI summary
A circuit is described that includes a rectifier configured to rectify a DC output from an AC input, a sensing unit configured to detect a voltage level of the DC output, and a control unit configured to control the rectifier based on the voltage level of the DC output. The control unit is configured to control the rectifier output by at least controlling the rectifier to rectify the DC output from the AC input if the voltage level of the DC output does not indicate an overvoltage condition at the circuit. In addition, the control unit is configured to control the rectifier based on the voltage level of the DC output by at least controlling the rectifier to shunt current from the AC input if the voltage level of the DC output does indicate the overvoltage condition.