Switching Mode Power Supply Frequency Control for Dynamic Response
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Solution Overview
Problem
Switching mode power supplies with primary side control face challenges in optimizing switching frequency under no-load conditions, leading to potential undershoot and poor dynamic load response due to limited bandwidth and blindness to output voltage changes before demagnetization.
Innovation Solution
Incorporating a light-load detector and frequency controller with transfer curves to adjust switching frequency based on load conditions, using a sample-and-hold circuit, transconductor, and de-magnetization detector to generate compensation voltage and determine de-magnetization time, thereby optimizing switching frequency and reducing undershoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If switching frequency is reduced under no-load condition to lower switching loss, then power conversion efficiency is improved, but dynamic load response deteriorates due to limited bandwidth and blindness to output voltage changes
Solution Approach 1:
The patent applies preliminary action by detecting light-load conditions in advance and proactively increasing the switching frequency before a sudden load change occurs. The controller detects when the load is light and pre-adjusts the switching frequency to a higher value, so that when a sudden load increase happens, the system is already prepared with adequate bandwidth to respond quickly, preventing undershoot while maintaining efficiency during light-load operation.
2Reliability
If switching frequency is increased to improve dynamic load response, then bandwidth is improved, but switching loss increases reducing power conversion efficiency
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable and adaptive rather than fixed. The controller dynamically changes the switching frequency based on real-time detection of load conditions - using high frequency during light-load conditions to ensure quick response capability, and automatically reducing to low frequency during heavy-load conditions to minimize switching losses and maximize power conversion efficiency.
3Device complexity
If primary side control is used to simplify the control structure, then device complexity is reduced, but measurement precision of output voltage deteriorates due to indirect sensing during demagnetization period
Solution Approach 1:
The patent applies feedback by continuously monitoring the demagnetization period duration and using this information to adjust the switching frequency. The controller measures the time it takes for the transformer to demagnetize, and based on this feedback, dynamically adjusts the switching frequency to optimize both dynamic response and efficiency, creating a closed-loop control system that improves measurement precision while maintaining the simplicity of primary side control.
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 enables better dynamic load response and reduced switching losses by adjusting switching frequency according to load conditions, minimizing undershoot and improving power conversion efficiency.
Implementation Method 1
A transformer comprises primary winding PRM, auxiliary winding AUX and secondary winding SEC, all inductively coupled to one another
Data Source
AI summary
A control method is used in a switching mode power supply to improve dynamic load response and switching loss. A PWM signal is provided to control a power switch and has a switching frequency. A cross voltage of a transformer in the switching mode power supply is detected to provide a de-magnetization time. The switching frequency is controlled in response to a sleep signal and a compensation voltage, which is generated based on an output voltage of the switching mode power supply. The sleep signal is provided in response to the de-magnetization time and a current sense signal, a representative of a winding current of the transformer. The switching frequency is not less than a first minimum value if the sleep signal is deasserted, and not less than a second minimum value if the sleep signal is asserted. The second minimum value is less than the first minimum value.