Quasi-Resonant Converter Frequency Jitter via Dynamic Capacitance
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Solution Overview
Problem
In quasi-resonant converters, implementing effective frequency jitter to reduce electromagnetic interference (EMI) is challenging due to the limited spread of switching frequencies during discontinuous conduction mode, which restricts the effectiveness of jittering techniques.
Innovation Solution
A power converter with a power switch and a time-varying capacitance coupled in parallel, where the capacitance adds frequency jitter to the switching frequency, comprising a first portion that varies with the input voltage and a second portion that is a time-varying function, allowing for a wider frequency range and reduced switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frequency jitter is implemented in quasi-resonant converters, then electromagnetic interference (EMI) is reduced, but the switching frequency spread is limited due to discontinuous conduction mode constraints
Solution Approach 1:
The patent implements dynamic capacitance adjustment during the discontinuous conduction mode period. A control circuit dynamically modifies the capacitance value in parallel with the power switch, which dynamically changes the resonant frequency. This dynamic adjustment allows the switching frequency to spread over a wider range while maintaining quasi-resonant operation, thereby reducing EMI without being constrained by fixed frequency limitations.
Solution Approach 2:
The patent changes the capacitance parameter during operation to achieve frequency jitter. By varying the capacitance value in parallel with the power switch during discontinuous conduction mode, the resonant frequency is shifted, creating frequency spread. This parameter change approach enables effective EMI reduction while overcoming the limited frequency range problem through controlled capacitance modulation.
2Device complexity
If fixed capacitance is used in parallel with power switch, then circuit simplicity is maintained, but frequency jitter range is insufficient for effective EMI reduction
Solution Approach 1:
The patent transitions from fixed capacitance to dynamic capacitance adjustment. The control circuit dynamically modifies the capacitance value during discontinuous conduction mode, enabling frequency jitter with sufficient spread range for effective EMI reduction. This dynamic approach maintains reasonable circuit simplicity while achieving the required frequency variation for EMI mitigation.
Solution Approach 2:
The patent implements variable capacitance parameter during operation to achieve adequate frequency jitter range. By controlling the capacitance value to change during discontinuous conduction mode, the system achieves sufficient frequency spread for EMI reduction while maintaining practical circuit implementation through controlled parameter modification.
3Loss of energy
If switching frequency is kept constant for efficient operation, then power efficiency is optimized, but EMI cannot be effectively reduced through frequency spreading
Solution Approach 1:
The patent implements periodic capacitance adjustment during each discontinuous conduction mode period. The control circuit periodically modifies the capacitance value, creating frequency jitter that spreads the switching frequency over time. This periodic action maintains overall power efficiency by operating within the resonant mode while effectively reducing EMI through frequency spreading across multiple switching cycles.
Solution Approach 2:
The patent introduces dynamic capacitance modulation during discontinuous conduction mode to create frequency jitter. This dynamic adjustment allows the system to maintain efficient resonant operation while spreading the switching frequency, thereby reducing EMI without significantly compromising power efficiency. The dynamic control ensures operation remains within optimal efficiency ranges while achieving EMI reduction.
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 effectively introduces frequency jitter to the quasi-resonant converter, reducing EMI and improving power efficiency by varying the oscillation period of the resonant waveform, thereby spreading the switching frequency across a larger range and minimizing switching losses.
Implementation Method 1
a resonant waveform of substantially sinusoidal oscillation of decreasing amplitude appears at the secondary winding and across the power switch due to the built-in inductance and capacitance in the converter
Implementation Method 2
a time-varying capacitance coupled in parallel to the power switch. The time-varying capacitance adds a frequency jitter to the frequency of the converter
Data Source
AI summary
A power converter includes a power switch controlling current flow in the power converter and a variable capacitance coupled in parallel to the power switch. The variable capacitance is configured to add a frequency jitter to the power converter.