Flyback Converter Light Load Efficiency Control
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Solution Overview
Problem
Traditional isolated switching converters face inefficiencies under no load and light load conditions, with limited no load efficiency and delayed responses to load transients due to reliance on auxiliary winding feedback, which results in undershoots in output voltage.
Innovation Solution
The proposed solution involves an isolated switching converter with a transformer having primary, secondary, and auxiliary windings, where the secondary controller acts as a master under light load conditions, generating a negative secondary current to control the primary switch, eliminating the need for feedback signals and allowing the primary switch to be fully turned off at zero output current, enhancing efficiency and response times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the converter operates in traditional mode with auxiliary winding feedback, then feedback control is achieved, but no load efficiency is limited because the main switch must remain on to provide feedback information
Solution Approach 1:
The patent implements dynamic mode switching between traditional feedback control and voltage control based on load conditions. Under light load, the system transitions to voltage control mode where the secondary switch is turned on after the primary switch turns off, allowing the primary switch to remain fully off and eliminating energy loss while maintaining output voltage regulation through direct voltage sensing rather than auxiliary winding feedback
Solution Approach 2:
The patent changes the control parameter from auxiliary winding voltage feedback to direct output voltage sensing under light load conditions. By monitoring the output voltage directly and controlling the secondary switch accordingly, the system achieves accurate voltage regulation without requiring the main switch to be on, thereby improving no-load efficiency while maintaining control reliability
2Power
If the converter works in DCM under light load, then switching frequency is low, but response to load transients is delayed causing output voltage undershoot
Solution Approach 1:
The patent implements preliminary action by having the secondary controller proactively turn on the secondary switch immediately after the primary switch turns off during light load conditions. This generates negative secondary current that quickly establishes voltage regulation, preparing the system to respond instantly to load transients before they cause voltage undershoot, thereby improving response speed without requiring high switching frequency
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 enhances no load efficiency and eliminates output voltage undershoots by directly controlling the secondary switch based on output voltage, enabling prompt responses to load transients without relying on feedback signals.
Implementation Method 1
a transformer having a primary winding, a secondary winding and an auxiliary winding, wherein the primary winding is configured to receive an input voltage, the secondary winding is coupled to provide an output voltage to a load
Data Source
AI summary
An isolated switching converter includes a transformer having a primary winding, a secondary winding and an auxiliary winding, a primary switch coupled to the primary winding, a secondary switch coupled to the secondary winding, and a feedback circuit coupled to the auxiliary winding to generate a feedback signal indicative of the output voltage. Under normal operation, the primary switch is controlled based on the feedback signal and the secondary switch is controlled based on the status of the primary switch. Under light load condition, the secondary switch is controlled based on the output voltage. The secondary switch is turned on to generate a negative secondary current flowing through the secondary winding and turned off when the negative secondary current reaches a secondary current threshold. The primary switch is turned on based on a negative primary current and turned off when the primary current reaches a primary current threshold.