Synchronous Rectifier Driving Circuit Parasitic Inductor Compensation
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Solution Overview
Problem
In synchronous rectifying switching power supplies, accurately sampling the real drain-source voltage between the drain and source terminals of the ideal transistor is challenging due to the voltage drop across the parasitic inductor, leading to inefficient turn-off moments and reduced efficiency.
Innovation Solution
A driving circuit that regulates the drain-source detecting voltage at a first reference voltage when it reaches a second reference voltage, where the first reference voltage is lower than the second, to accurately control the synchronous rectifier's turn-off moment and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the drain-source detecting voltage VDSS is used to control the turn-off moment of the synchronous rectifier, then the turn-off control is simplified, but the turn-off moment becomes inaccurate due to the voltage drop across the parasitic inductor
Solution Approach 1:
The patent introduces an intermediary processing stage between the drain-source detecting voltage VDSS and the turn-off control. A processing circuit calculates the real drain-source voltage VDS by compensating for the voltage drop across the parasitic inductor. This intermediary calculation ensures accurate turn-off moment detection while keeping the overall control system manageable.
Solution Approach 2:
The patent replaces direct voltage threshold comparison with a computational approach. Instead of directly comparing VDSS with a threshold voltage, the system uses a processing circuit to compute the real drain-source voltage VDS by subtracting the parasitic inductor voltage drop from VDSS, then compares the computed VDS with the threshold. This substitution of mechanical/electrical direct comparison with computational processing resolves the accuracy issue.
2Measurement precision
If the turn-off moment is advanced to compensate for parasitic inductor voltage drop, then the real drain-source voltage reaches the reverse voltage threshold more accurately, but the synchronous rectifier turns off earlier causing reduced efficiency
Solution Approach 1:
The patent implements a feedback mechanism where the processing circuit continuously monitors the drain-source detecting voltage VDSS, calculates the real drain-source voltage VDS by compensating for parasitic inductor effects, and uses this feedback information to determine the precise turn-off moment. This feedback loop ensures the synchronous rectifier turns off at the optimal moment when VDS reaches the reverse voltage threshold, maximizing efficiency while maintaining accurate threshold detection.
3Reliability
If traditional voltage regulation methods are used to prevent false triggering, then the drain-source detecting voltage is regulated at the preset value, but the on-resistance of the synchronous rectifier increases reducing efficiency
Solution Approach 1:
The patent replaces traditional voltage regulation methods that directly control VDSS with a computational substitution approach. Instead of regulating VDSS to prevent false triggering, the system calculates the real drain-source voltage VDS by compensating for parasitic inductor voltage drop in software/mathematical processing. This substitution allows accurate threshold detection without increasing the synchronous rectifier's on-resistance, thereby maintaining efficiency while preventing false triggering.
Data Source
AI summary
A driving circuit and driving method for driving a synchronous rectifier. When a drain-source detecting voltage between a drain terminal and a source terminal of the synchronous rectifier reaches a second reference voltage, the driving voltage applied at a gate terminal of the synchronous rectifier is decreased to regulate the drain-source detecting voltage to a first reference voltage. The first reference voltage is lower than the second reference voltage. And when the drain-source detecting voltage reaches an off reference voltage, the synchronous rectifier is turned off.