Adaptive Valley Control for Quasi-Resonant Flyback Switching Loss
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Solution Overview
Problem
Existing quasi-resonant flyback switching power supplies face inefficiencies due to high switching loss when bus voltage is high, as fixed frequency control methods fail to optimize efficiency across varying input/output voltages, leading to increased design complexity and cost.
Innovation Solution
A switching cycle adaptive control method partitions bus voltage and output power into different ranges, setting unique reference and power valley numbers for each range, adjusting the PWM signal frequency to minimize switching loss by extending the PWM cycle at high voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed frequency control method is used, then the control is simple, but the switching loss increases when bus voltage is high
Solution Approach 1:
The patent applies dynamics by transitioning from fixed frequency control to adaptive frequency control. The PWM frequency dynamically adjusts based on real-time bus voltage detection, allowing the system to optimize switching frequency for current operating conditions. This resolves the contradiction by making the control frequency variable rather than static, reducing switching loss at high voltages while maintaining simplicity through automated adaptation.
Solution Approach 2:
The patent changes the frequency parameter of the PWM signal based on bus voltage levels. By detecting bus voltage and selecting from multiple preset frequency curves, the system modifies the operating frequency parameter to match voltage conditions. This parameter adaptation reduces switching loss during high-voltage operation while keeping the control structure relatively simple through pre-defined frequency options.
2Adaptability or versatility
If multiple preset fixed frequency-load curves are used, then the adaptability to wide input/output voltages improves, but the design complexity and cost increase
Solution Approach 1:
The system dynamically selects from multiple preset frequency curves based on detected bus voltage and load conditions. Rather than using a single fixed curve, the control adapts by switching between pre-defined frequency-load curves that are optimized for different operating ranges. This provides wide voltage adaptability while keeping design complexity manageable through automated curve selection rather than manual configuration.
Solution Approach 2:
The patent segments the operating range into multiple frequency curves, each optimized for specific voltage and power conditions. By dividing the control strategy into distinct frequency curves (first, second, third curves) with different characteristics, the system achieves adaptability across wide voltage ranges. Each segment handles specific operating conditions, avoiding the need for a single complex curve while reducing overall design complexity through modular frequency options.
3Power
If the PWM frequency is increased to maintain switching performance, then the switching loss increases, but the power delivery improves
Solution Approach 1:
The patent changes the PWM frequency parameter based on bus voltage detection. At high bus voltages, the system automatically reduces frequency to minimize switching loss, while at lower voltages it uses higher frequencies to maintain adequate power delivery. This dynamic parameter adjustment optimizes the trade-off between power delivery capability and switching loss by matching frequency to voltage conditions.
Solution Approach 2:
The system dynamically adjusts PWM frequency rather than using a fixed value. By continuously monitoring bus voltage and adapting frequency in real-time, the system maintains effective power delivery across varying conditions while minimizing switching loss during high-voltage operation. This dynamic approach resolves the contradiction by allowing frequency to flex with operating conditions.
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 method effectively suppresses high switching loss by optimizing the PWM frequency based on varying bus voltages and output powers, enhancing efficiency and reducing design complexity.
Implementation Method 1
acquiring a bus voltage and determining the voltage partition to which the acquired bus voltage belongs
Implementation Method 2
performing closed-loop control on a reference voltage and an output voltage of the switching power supply to acquire an output power
Implementation Method 3
When a current flowing through an energy storage element drops to zero, the parasitic capacitances of the energy storage element and the power switch begins to resonate. When the resonant voltage across the power switch is at its minimum voltage, a main switch is turned on (conduction at valley bottom)
Implementation Method 4
After inductive demagnetization is determined according to the load power, the next pulse-width modulation (PWM) is turned on after passing several valleys
Implementation Method 5
adjusting the frequency of a PWM signal of the switching power supply according to the number of valleys required to pass, so as to adaptively adjust the switching cycle to reduce the switching power consumption
Data Source
AI summary
The provided is a switching cycle adaptive control method for a switching power supply. The method includes: setting a voltage threshold for a bus voltage and forming voltage partitions; acquiring a bus voltage and determining the voltage partition to which the acquired bus voltage belongs; setting a power threshold for an output power of a switching power supply and forming power partitions; performing closed-loop control on a reference voltage and an output voltage of the switching power supply and determining the power partition to which the acquired output power belongs; setting different reference valley numbers P; setting different power valley numbers Q; determining a real-time reference valley number P and a real-time power valley number Q; adding the reference valley number P and the power valley number Q to obtain the number of valleys; and adjusting the frequency of a PWM signal of the switching power supply.