Synchronous Rectifier Control for Isolated Power Converter
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Solution Overview
Problem
Existing isolated power converters face efficiency losses due to diode rectifiers and synchronous rectifiers, particularly during startup and light load operations, leading to reverse current issues and circulating currents in parallel configurations.
Innovation Solution
A power converter circuit with a control circuit that operates synchronous rectifiers synchronously with primary switches during high inductor current and switches to a bidirectional mode at lower inductor current, allowing energy transfer in both directions and minimizing conduction losses, with the option to switch to a diode mode to prevent reverse current under low input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectifiers are used with complementary timing to primary switches, then conduction resistance is minimized and rectifier efficiency is improved, but reverse current can be transferred from secondary side to primary side causing damage to internal circuit components
Solution Approach 1:
The patent applies dynamics by making the synchronous rectifier timing mode adjustable rather than fixed. The control circuit dynamically switches between synchronous timing mode (for heavy loads) and non-synchronous timing mode (for light loads), optimizing performance while preventing reverse current damage. This resolves the contradiction by adapting the timing strategy to actual operating conditions rather than using a static complementary timing approach.
Solution Approach 2:
The patent changes the timing parameter of the synchronous rectifiers based on load conditions. When the timing relationship between synchronous rectifiers and primary switches is changed from complementary to non-complementary (desynchronized), reverse current flow is prevented while maintaining acceptable rectification efficiency. This parameter adjustment resolves the contradiction between minimizing conduction loss and preventing component damage.
Data Source
AI summary
An apparatus comprises a power converter circuit and a control circuit. The power converter circuit includes a primary circuit side and a secondary circuit side. The primary circuit side includes a plurality of primary switches, and the secondary circuit side includes a plurality of synchronous rectifiers and an inductor. The control circuit is configured to operate the synchronous rectifiers synchronously with the primary switches when inductor current at the inductor is greater than or equal to a reference inductor current, and operate the synchronous rectifiers in a bidirectional mode when the inductor current is less than the reference inductor current, wherein energy is delivered from the primary side to the secondary side and from the secondary side to the primary side during the bidirectional mode.