QR Flyback Converter Valley Control for Low-Load Efficiency
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Solution Overview
Problem
Previous generations of quasi-resonant (QR) flyback converters experience inefficiency due to increasing switching frequency with decreasing load current, leading to higher power losses and reduced efficiency across varying loads and voltage ranges.
Innovation Solution
A secondary side controller with a programmable valley algorithm is introduced, utilizing an analog-to-digital converter, look-up-table, and pulse width modulator to determine the optimal valley for switching, allowing for incremental or decremental adjustments in switching cycles to maintain high efficiency across a wide range of loads and voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If free running QR mode is used with MOSFET turning on at first valley point, then simplicity of control is improved, but efficiency deteriorates at low loads due to increased switching frequency
Solution Approach 1:
The patent implements dynamic valley selection where the converter can switch between different valley points (first, second, third, etc.) based on operating conditions. The controller dynamically adjusts which valley to use for MOSFET turn-on, transitioning from fixed first-valley operation to adaptive multi-valley operation. This dynamic approach allows optimization of switching frequency and efficiency across different load conditions while maintaining reasonable control complexity.
Solution Approach 2:
The patent changes the operating parameter of valley selection by introducing a programmable valley counter that can be set to different values (first valley, second valley, third valley, etc.). This parameter change allows the system to select optimal valleys based on load conditions, thereby reducing switching frequency and power losses at low loads while maintaining efficiency at higher loads.
2Adaptability or versatility
If switching frequency increases with decreasing load current, then automatic adaptation to load is improved, but efficiency deteriorates due to higher power losses
Solution Approach 1:
The patent implements feedback mechanisms where the controller monitors operating conditions (load current, voltage, temperature) and uses this information to adjust the valley selection and switching frequency. The feedback loop allows the system to adapt to changing load conditions while actively controlling switching frequency to minimize power losses, rather than allowing frequency to increase automatically with decreasing load.
Solution Approach 2:
The patent applies preliminary anti-action by proactively reducing switching frequency before power losses become excessive. The programmable valley algorithm anticipates the relationship between load current and switching frequency, and pre-adjusts the valley selection to prevent the automatic frequency increase that would cause higher losses at low loads.
3Loss of energy
If programmable valley algorithm with multiple components is implemented, then efficiency across varying loads is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal controller architecture that handles multiple functions: valley detection, valley counting, load monitoring, frequency adjustment, and switching control. This multi-functional approach consolidates what could be multiple separate components into a single integrated controller, improving efficiency across varying loads while limiting the increase in device complexity through functional integration.
Solution Approach 2:
The programmable valley algorithm is designed to be self-adjusting based on operating conditions. The controller automatically selects appropriate valleys and adjusts switching frequency without requiring complex external control circuits or manual intervention. This self-service capability reduces the need for additional control components, thereby limiting complexity increase while achieving improved efficiency.
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 ensures high efficiency across a wide range of output loads and voltages, with efficiency greater than 89% for loads over 40% and maintaining efficiency above 84% even at low loads, significantly improving power delivery in applications like USB-PD.
Implementation Method 1
a transformer 104, a first rectifying element or power switch (PS), such as a metal-oxide-silicon field effect transistor (MOSFET 106), on a primary side of the transformer, a second rectifying element
Implementation Method 2
Component Lleak 114 represents a parasitic leakage inductance of the transformer 104, while CP 116 represents a total parasitic capacitance (intra-winding capacitance and stray capacitance) of the primary side of the flyback converter 100. During this time both windings are open, thus, the inductance of the primary side of the transformer 104, LP, resonates with the capacitance at the parasitic capacitance (CP 116).
Data Source
AI summary
A secondary-side-controller for a QR flyback converter and method for operating the same are provided. Generally, the secondary-side-controller includes a driver configured to control a power-switch (PS) on a primary side of converter to turn on the PS when a sinusoidal input voltage to the converter is at one of a plurality of valleys, an analog-to-digital-converter (ADC) to read the input voltage, output voltage, and load current, and generate digital signals based thereon. A valley-controller coupled to the driver, ADC, a look-up-table and a pulse width modulator (PWM) receives the signals from the ADC and using the look-up-table determines at which valley of the plurality of valleys to couple a PWM signal from the PWM to the driver. The valley-controller is operable for each switching cycle of the PS to increment, decrement or leave unchanged the valley at which the PWM signal is coupled from the PWM to the driver.