Synchronous Rectification Control for Reverse Current in Resonant Converters
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Solution Overview
Problem
Existing switching power source devices with current resonant type converters experience significant power loss due to reverse current flow, especially during light load conditions, which affects efficiency and can lead to circuit malfunctions.
Innovation Solution
A switching power source device with a series resonant circuit incorporating a current resonant inductor and capacitor, where synchronous rectification switch elements are controlled using a maximum on width control circuit and synchronous control circuit to synchronize the on-off timing with the main switch elements, preventing reverse current flow by detecting internal diode conduction and adjusting the on period of the synchronous rectification switch elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification switch elements are used to reduce power loss from forward drop voltage, then power loss due to diode forward voltage is reduced, but reverse current flow occurs causing power loss and circuit malfunction
Solution Approach 1:
The patent implements feedback control by detecting the inter-terminal voltage of synchronous rectification switch elements to determine diode conduction timing. The control circuit uses this feedback information to precisely control the on-off timing of the synchronous rectification switch elements, ensuring they turn off before reverse current occurs while maintaining low conduction loss during normal operation.
Solution Approach 2:
The control circuit performs preliminary action by predicting and preventing reverse current flow. By detecting diode conduction timing through voltage sensing and proactively controlling the switch elements to turn off at the appropriate moment, the system prevents reverse current before it can occur, rather than reacting after the problem arises.
2Productivity
If the on period of synchronous rectification switch elements is extended to improve rectification efficiency, then rectification efficiency is improved, but reverse current flow increases causing power loss
Solution Approach 1:
The patent uses feedback control to optimize the on period duration. By continuously monitoring the inter-terminal voltage to detect diode conduction timing, the control circuit dynamically adjusts the on period length to match actual operating conditions, maximizing rectification efficiency while preventing reverse current flow that would cause power loss.
Solution Approach 2:
The system implements dynamic control of the synchronous rectification switch elements' on period. Rather than using a fixed on period, the control circuit dynamically adjusts the conduction time based on real-time detection of diode conduction timing through voltage sensing, optimizing performance across varying load conditions.
3Loss of energy
If rectification diodes are replaced with synchronous rectification switch elements, then forward drop voltage loss is reduced, but control complexity increases to prevent reverse current
Solution Approach 1:
The patent reduces control complexity through feedback-based automatic control. By using voltage sensing to detect diode conduction timing and automatically controlling the synchronous rectification switch elements based on this feedback, the system eliminates the need for complex timing circuits or external synchronization signals, achieving simple and reliable control.
Solution Approach 2:
The control system performs self-service by using the inherent voltage characteristics of the circuit to generate its own control signals. The inter-terminal voltage of the synchronous rectification switch elements themselves provides the sensing signal needed for control, eliminating the need for separate sensing circuits or external control inputs.
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 effectively eliminates noise and prevents reverse current flow in all operational modes, ensuring stable synchronous rectification and reducing power loss, thereby enhancing the efficiency and reliability of the switching power source device.
Implementation Method 1
a series resonant circuit which includes a current resonant inductor Lr and a current resonant capacitor Cr
Implementation Method 2
a power converting transformer T, a plurality of synchronous rectification switch elements Qs1, Qs2... inducing a current from the series resonant circuit to a secondary side
Implementation Method 3
synchronous rectification switch elements Qs1, Qs2, in which internal diodes Ds are connected in parallel... by detecting a timing of conduction of the internal diodes
Data Source
AI summary
A switching power source device for supplying power to a load includes a series resonant circuit, a plurality of main switch elements or main switch element groups for switching a current path of the series resonant circuit, a transformer for inducing a secondary current from the series resonant circuit, a plurality of synchronous rectification switch elements for rectifying the secondary current, a maximum on width control circuit for ordering a start and a completion of a maximum on width to the synchronous rectification switch element in synchronization with a timing of turning on the main switch elements or the main switch element groups, and a synchronous control circuit. The circuit controls an on period of the synchronous rectification switch element so as to turn on the synchronous rectification switch element in synchronization with a particular timing, and turn off in synchronization with another timing.