Valley-Edge PFM Controller for Switching Power Supplies
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Solution Overview
Problem
Conventional Pulse Frequency Modulation (PFM) controllers for switching mode power supplies face inefficiencies in power utilization and electromagnetic interference (EMI) due to large turn-on transition losses and fixed switching frequency spectra.
Innovation Solution
A PFM controller that turns on the power transistor at the valley of the resonant voltage ringing waveform, using an oscillator with twice the oscillation frequency to determine control signal timing, reducing turn-on transition losses and introducing random frequency dithering to spread the switching frequency spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the power transistor is turned on at the peak of the resonant voltage ringing waveform, then the control is simple, but large turn-on transition losses occur
Solution Approach 1:
The patent uses an oscillator to generate a reference signal at twice the resonant frequency, which anticipates the valley points of the resonant waveform. By comparing this reference signal with the actual resonant voltage, the control system prepares to turn on the transistor at the optimal moment (valley point) before the resonant cycle completes, thereby reducing turn-on losses while maintaining simple control logic.
Solution Approach 2:
The patent implements a feedback mechanism where the resonant voltage waveform is continuously monitored and compared with a reference signal from an oscillator. This feedback loop enables the system to dynamically identify valley points and adjust the transistor switching timing accordingly, optimizing power efficiency while maintaining simple control architecture.
2Device complexity
If a fixed switching frequency is used, then the control topology is simple, but electromagnetic interference occurs due to concentrated frequency spectrum
Solution Approach 1:
The patent introduces dynamic frequency variation by using an oscillator whose output frequency is modulated based on the resonant waveform detection. Instead of a fixed frequency, the switching frequency dynamically adjusts to follow the resonant characteristics, spreading the spectral energy and reducing EMI while maintaining relatively simple control topology through natural resonance exploitation.
Solution Approach 2:
The patent employs periodic oscillation at twice the resonant frequency to generate timing signals that naturally vary the switching frequency. This periodic action creates intentional frequency modulation that spreads the spectral content over a wider range, reducing concentrated EMI while keeping the control mechanism simple and rhythmically predictable.
3Use of energy by stationary object
If conventional PFM control is used, then the quiescent current is small, but power utilization efficiency is poor due to large transition losses
Solution Approach 1:
The patent changes the critical parameter of switching timing from arbitrary or peak-based to valley-point synchronization. By detecting and locking onto the valley points of the resonant waveform through oscillator comparison, the system transforms the switching parameter to achieve minimal transition losses while preserving the low quiescent current characteristic of conventional PFM 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
This approach reduces power transistor turn-on transition losses and suppresses EMI by randomly changing the switching frequency, enhancing power conversion efficiency and reducing electromagnetic interference.
Implementation Method 1
a resonant ringing voltage waveform often exists when the control pulse is turned off
Implementation Method 2
using an oscillator having twice the oscillation frequency of the resonant ringing waveform for determining the timing of the control signals
Implementation Method 3
introduces random dithering in the power transistor's switching frequency
Data Source
AI summary
A pulse frequency modulation (PFM) controller for controlling a switching mode power supply. The controller includes an output terminal for providing a control signal to turn on and off a current in the power supply to regulate an output of the power supply. A first input terminal receives a feedback signal related to the output of the power supply, the feedback signal exhibiting a ringing waveform when the current in the power supply is turned off. The controller also includes a control circuit configured to provide the control signal in response to the feedback signal. The control signal is adapted to turn on the current in the power supply when the feedback signal is substantially at a valley of the ringing waveform of the feedback signal. In an embodiment, such a PFM controller can reduce turn-on transition loss in a power supply and provides frequency dithering to reduce electromagnetic interference.