Resonant Flyback Half-Bridge Control for Light-Load Current Reduction
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Solution Overview
Problem
Existing resonant flyback power converters suffer from low power efficiency during light load conditions and inability to vary output voltage, with high circulating currents causing power loss and inefficiency.
Innovation Solution
A resonant flyback power converter with a switching control circuit that includes a half-bridge circuit, a transformer, and a resonant capacitor, utilizing a current-sense device to generate driving signals for efficient magnetizing and discharging, with over-current protection mechanisms to prevent transistor damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed minimum SL on-time is used to discharge the resonant capacitor, then the resonant capacitor can be properly discharged, but high circulating current is generated during light load causing power loss
Solution Approach 1:
The patent applies dynamics by making the SL on-time adjustable rather than fixed. The control circuit dynamically adjusts the SL on-time based on load conditions: during light load, the SL on-time is reduced or eliminated to prevent high circulating current and power loss, while during heavy load, the SL on-time is extended to ensure proper resonant capacitor discharge. This dynamic adjustment resolves the contradiction between reliable capacitor discharge and energy efficiency.
Solution Approach 2:
The patent changes the parameter of SL on-time duration based on operating conditions. By monitoring load current or power level, the control circuit adjusts the SL pulse width parameter: reducing it during light load to minimize circulating current and power loss, and increasing it during heavy load to ensure complete resonant capacitor discharge. This parameter adaptation resolves the technical contradiction.
2Use of energy by moving object
If the switching frequency is decreased to save power during light load, then power consumption is reduced, but power efficiency remains low due to circulating current
Solution Approach 1:
The patent uses periodic action by implementing discontinuous conduction mode (DCM) with adjustable switching frequency. During light load, the switching frequency is reduced and the converter operates in DCM, where the secondary current completes its cycle before the next switching cycle begins. This periodic operation with extended off-time eliminates circulating current while maintaining acceptable power consumption, resolving the contradiction between power consumption and power efficiency.
Solution Approach 2:
The patent applies dynamics by making the switching frequency adjustable based on load conditions. The control circuit dynamically changes the switching frequency: lowering it during light load to reduce power consumption while using DCM to eliminate circulating current, and raising it during heavy load to maintain adequate power transfer. This dynamic frequency adjustment resolves the contradiction between power consumption and power efficiency.
3Reliability
If over-current protection is added to prevent transistor damage, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies feedback by implementing current sensing that monitors the primary switching current and provides feedback to the control circuit. The control circuit compares the sensed current against predetermined thresholds and automatically adjusts switching or triggers protection actions when over-current conditions are detected. This feedback mechanism provides reliable transistor protection while keeping the control circuit relatively simple by using straightforward threshold comparison logic.
Solution Approach 2:
The patent applies self-service by making the protection circuit monitor its own operating conditions and automatically take protective action without external intervention. The current sensing circuit continuously monitors the switching current and the control circuit automatically shuts down or adjusts operation when over-current is detected, providing self-protecting functionality that improves reliability without requiring complex external protection circuits.
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
Improves power efficiency during light load operations by reducing circulating currents and providing over-current protection, ensuring reliable operation and reduced power loss.
Implementation Method 1
a resonant capacitor (20) connected in series with the transformer (10) and coupled to the half-bridge circuit for resonant discharge
Implementation Method 2
a transformer (10) and a resonant capacitor (20) which are connected in series and are coupled to the half-bridge circuit
Data Source
AI summary
A resonant flyback power converter includes: a first and a second transistors which form a half-bridge circuit for switching a transformer and a resonant capacitor to generate an output voltage; a current-sense device for sensing a switching current of the half-bridge circuit to generate a current-sense signal; and a switching control circuit generating a first and a second driving signals for controlling the first and the second transistors. The turn-on of the first driving signal controls the half-bridge circuit to generate a positive current to magnetize the transformer and charge the resonant capacitor. The turn-on of the second driving signal controls the half-bridge circuit to generate a negative current to discharge the resonant capacitor. The switching control circuit turns off the first transistor when the positive current exceeds a positive-over-current threshold, and/or, turns off the second transistor when the negative current exceeds a negative-over-current threshold.