Power Equalization Circuit for Transformer Cross-Regulation
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Solution Overview
Problem
In power converters operating in discontinuous conduction mode, cross-regulation of multiple output voltages worsens during light load conditions, leading to voltage drift and potential power insufficiency, especially when used to power critical circuits like primary side controllers.
Innovation Solution
A power equalization circuit comprising a threshold detection circuit, timer circuit, overdrive current source, and commutator circuit that connects transformer windings to ground to equalize output voltages and prevent primary MOSFET switch activation during equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the converter operates in discontinuous conduction mode to conserve energy during light load operation, then energy efficiency is improved, but cross-regulation between multiple outputs worsens and output voltages drift
Solution Approach 1:
The patent implements periodic action by using a drift timer to periodically trigger equalization cycles. When the timer expires (indicating light load DCM operation has been occurring), the system activates commutator circuits to periodically equalize output voltages. This periodic intervention maintains cross-regulation stability without requiring continuous operation, thus preserving energy efficiency while preventing voltage drift.
Solution Approach 2:
The patent introduces intermediary components including drift timer circuits, commutator circuits, and equalization switches that mediate between the conflicting requirements. These intermediaries detect the DCM state and actively equalize output voltages by redirecting energy between outputs, serving as a bridge between energy conservation goals and voltage stability requirements.
2Loss of energy
If the switching frequency is reduced to maintain high efficiency in DCM operation, then energy loss is reduced, but output voltage stability deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where output voltages are continuously monitored and compared against reference values. The error signals generated feed back to control the commutator circuits and equalization process, ensuring that voltage stability is maintained through closed-loop control rather than relying solely on fixed-frequency switching.
Solution Approach 2:
Instead of maintaining high-frequency switching for stability, the system uses periodic equalization actions triggered by the drift timer. This allows the system to operate at lower frequencies for efficiency while periodically correcting voltage deviations through controlled energy redistribution among outputs.
3Reliability
If additional commutator circuits and control circuits are added to equalize power, then cross-regulation improves, but device complexity increases
Solution Approach 1:
The patent applies self-service principles where the power converter uses its own output energy to drive the commutator circuits and equalization process. The system equalizes its own outputs by redirecting energy from higher-voltage outputs to lower-voltage outputs using the existing transformer windings and commutator switches, without requiring external intervention or additional complex control infrastructure.
Solution Approach 2:
The commutator circuits are designed to serve multiple functions: they enable equalization of multiple output voltages, provide feedback signaling to the primary side controller, and can operate with existing transformer windings. This multi-functionality reduces the need for separate dedicated equalization hardware, thereby limiting the increase in device complexity.
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
The solution effectively reduces cross-regulation issues and maintains stable output voltages across multiple isolated outputs, ensuring reliable operation even during light load conditions by periodically equalizing power and preventing primary MOSFET switch activation during the process.
Implementation Method 1
a transformer with a main primary winding for receiving a power signal to be converted, and a main secondary winding for providing a converted power signal
Implementation Method 2
When the MOSFET switch is closed in a flyback converter, the current through the main primary coil of the transformer rises, increasing the energy stored in the transformer
Data Source
AI summary
A power equalization circuit in a transformer-based device having a plurality of isolated voltage outputs is provided. The circuit comprises: a threshold detection circuit configured to receive an error signal derived from a selected voltage at one of the isolated voltage outputs, and to determine whether the selected voltage is above a voltage threshold based on the error signal; a timer circuit configured to activate a wait signal after a maximum voltage drift time has expired since the selected voltage rose above the voltage threshold, and to activate a wink signal coincident with the wait signal; an overdrive current source configured to drive an error current to an overdriven value in response to the wait signal; and a commutator circuit connected to a transistor winding associated with the selected isolated voltage output, the commutator being configured to connect a transformer secondary winding to ground in response to the wink signal.