Synchronous Rectifier Input Circuit for Switch-Mode Power Supply
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Solution Overview
Problem
Modern switched-mode power supplies face challenges in miniaturization due to the limitations of input wiring, which reduces reliability, is not reversible, and lacks protection against overvoltage, especially in countries with poor power quality.
Innovation Solution
Replacing two diodes in the rectifier with controllable switches acting as synchronous rectifiers, using IGBTs, and implementing a current-limiting resistor with reduced dimensions, allowing for reversible protection and enhanced safety features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If four diodes are used in the rectifier, then rectification function is provided, but mechanical dimensions and weight are large
Solution Approach 1:
The patent changes the fundamental operating parameters of the rectifier by replacing passive diodes with active controllable switches (MOSFETs or IGBTs). This allows the rectification process to be controlled in synchronization with the mains frequency, enabling current limitation and reduced component stress without compromising the rectification function. The parameter change from passive to active switching enables miniaturization while maintaining reliability.
2Reliability
If resistor Rlimit is used for current limitation, then starting current is limited, but the function is not reversible and reliability is reduced
Solution Approach 1:
The patent transforms the static, irreversible current limitation function of resistor Rlimit into a dynamic, reversible function using controllable switches. The switches can be turned on and off in synchronization with the mains frequency, providing active current limitation during startup that can be dynamically adjusted and reversed when no longer needed. This dynamic approach maintains reliability during startup while preserving full functionality during normal operation.
3Volume of stationary object
If input wiring is reduced in size and components, then miniaturization is achieved, but protection against overvoltage and transient pulses is lost
Solution Approach 1:
The patent implements preliminary protective action by using controllable switches that can be pre-configured to limit current and block overvoltage transients before they damage other components. The switches are controlled to conduct during normal operation but can quickly block transient overvoltage pulses, providing proactive protection. This preliminary protective mechanism is integrated into the miniaturized circuit design, eliminating the need for separate protection components.
4Volume of stationary object
If mechanical dimensions of rectifier diodes are reduced, then miniaturization is achieved, but electrical load stress increases and service life is reduced
Solution Approach 1:
The patent changes the operating parameters of the rectification process by using controllable switches with low on-resistance that can be actively managed. This allows the switches to handle electrical stress more efficiently than passive diodes, reducing peak current stress and thermal loading. The active control enables the switches to operate within optimal parameter ranges, extending service life while allowing for smaller physical dimensions.
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 solution enables miniaturization, increased reliability, and reversible operation, while providing effective protection against overvoltage and reducing component size and costs, allowing for efficient integration into terminal devices.
Implementation Method 1
two controllable switches, which act as synchronous rectifiers and are connected in such a way that they can be switched on and off by alternate forced control. The two controllable switches are thereby alternately switched on and off in the rhythm of the mains frequency
Implementation Method 2
the resistor Rlimit fulfills several functions: It allows a starting current limitation to values below the maximum surge current Isurge of the four diodes of the rectifier
Data Source
AI summary
The invention relates to an input circuit for a logic circuit part, comprising a voltage converter component for conversion of a mains voltage to the required low voltage in order to supply a user with a low voltage. The supply to the input circuit may hence be connected to a mains supply to rectify the mains voltage and an output from the input circuit may be connected to the voltage converter component to provide a rectified input voltage for the voltage converter component. According to the invention, an improved input circuit for a logic circuit part with improved functionality and operating security also permitting an extensive miniaturization and simplified production may be achieved by replacement of at least two of the remaining four diodes in the rectifier part of an input circuit for a logic circuit part by two controllable switches which work as a synchronous rectifier and are connected such as to be switched on and off by alternate forced control.