Switching Controller Frequency Hopping EMI Reduction
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Solution Overview
Problem
Power converters using pulse width modulation generate high-frequency signals that result in significant electric and magnetic interference (EMI), necessitating the use of EMI filters which increase power consumption and costs.
Innovation Solution
A switching controller with frequency hopping capability, utilizing a first oscillator for generating a pulse signal and a pattern generator with a programmable capacitor to modulate the switching frequency, eliminating the need for EMI filters by limiting the maximum on-time of the switching signal through a maximum duty-cycle signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse width modulation is used to convert AC power source to regulated voltage, then power conversion efficiency is improved, but electric and magnetic interference (EMI) increases
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The switching controller dynamically adjusts the switching frequency within a range (e.g., 60kHz-100kHz) based on operating conditions, allowing the system to maintain high conversion efficiency while reducing EMI by avoiding fixed high-frequency operation.
Solution Approach 2:
The patent changes the frequency parameter of the switching signal from a constant high value to a variable value within a specified range. This parameter change allows the power converter to achieve both high efficiency (through optimized switching) and reduced EMI (through frequency variation), directly resolving the technical contradiction.
2Object-generated harmful factors
If EMI filter is added to reduce electric and magnetic interference, then EMI is reduced, but power consumption increases and cost increases
Solution Approach 1:
The patent extracts the EMI reduction function from the traditional EMI filter approach and implements it directly in the switching controller through frequency modulation. By taking out the need for external EMI filtering and incorporating EMI mitigation capabilities into the switching control itself, the system reduces both EMI and the associated power consumption and cost overhead.
Solution Approach 2:
The switching controller performs self-service by inherently reducing EMI through its frequency modulation capability without requiring external EMI filters. The controller serves dual purposes: power conversion control and EMI mitigation, eliminating the need for separate EMI reduction components and their associated power consumption.
3Productivity
If switching frequency is increased to improve power conversion efficiency, then conversion efficiency is improved, but EMI increases
Solution Approach 1:
The patent applies dynamics by implementing a dynamic switching frequency that adapts to operating conditions. Rather than using a fixed high frequency, the controller dynamically adjusts the frequency within an optimized range, maintaining high conversion efficiency when needed while reducing EMI when possible, thus resolving the contradiction between efficiency and EMI.
Data Source
AI summary
A switching controller having switching frequency hopping for a power converter includes a first oscillator generating a pulse signal and a maximum duty-cycle signal for determining a switching frequency of a switching signal, a pattern generator having a second oscillator and generating a digital pattern code in response to a clock signal, a programmable capacitor coupled to the pattern generator and the first oscillator for modulating the switching frequency of the switching signal in response to the digital pattern code, and a PWM circuit coupled to the first oscillator for generating the switching signal in accordance with the maximum duty-cycle signal. A maximum on-time of the switching signal is limited by the maximum duty-cycle signal. The switching signal is utilized to switch a transformer of the power converter.