Frequency Jittering Circuit for Switching Power Supply EMI Reduction
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Solution Overview
Problem
Conventional switching mode power supplies generate strong electromagnetic interference (EMI) due to fixed switching frequencies, and existing frequency jittering methods require large capacitors, making them costly and impractical for chip circuit integration.
Innovation Solution
A frequency jittering circuit that modulates the hysteretic band of an oscillator using a hysteretic band modulator and gain circuit to generate a clock with a jittering frequency, allowing the switching frequency of a power supply to vary by adjusting the upper limit of the hysteretic band over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixed switching frequency is used in a switching mode power supply, then the power supply operates efficiently, but strong electromagnetic interference (EMI) noise is generated at the switching frequency and its harmonics
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The oscillator circuit continuously varies the switching frequency around a central value, transforming the static frequency operation into dynamic frequency modulation. This frequency variation distributes the EMI energy across a broader spectrum, reducing peak noise levels while maintaining overall power supply efficiency.
Solution Approach 2:
The patent implements periodic action through the oscillator circuit that periodically modulates the switching frequency. The frequency varies in a periodic manner, creating a triangular waveform pattern that continuously shifts the switching frequency up and down. This periodic frequency modulation effectively spreads EMI energy over time and frequency, reducing concentrated noise emissions.
2Object-generated harmful factors
If frequency jittering is implemented by adjusting charging and discharging currents in the oscillator circuit, then EMI emission is reduced, but a huge capacitor is required which increases cost and reduces chip circuit integration
Solution Approach 1:
The patent applies parameter changes by modifying the oscillator's operating parameters (resistances and voltages) rather than changing the capacitor size. The frequency modulation is achieved by varying the charging and discharging currents through controlled changes in resistance values and voltage levels, allowing frequency jittering without requiring large capacitor values. This maintains small component sizes suitable for chip integration.
Solution Approach 2:
The patent uses a simplified oscillator circuit design that copies the essential frequency modulation function without requiring the complex large-capacitor-based implementation. By replicating the frequency variation effect through alternative circuit topology with smaller components, the patent achieves the same EMI reduction benefit with reduced complexity and better integrability.
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 effectively reduces EMI by distributing noise energy across a broader band, improving EMI performance while minimizing the need for large capacitors, thus being more cost-effective and suitable for chip circuit integration.
Implementation Method 1
the voltage Vosc on the capacitor C-osc is lower than a lower limit VREF1
Implementation Method 2
a comparator 102 will trigger a comparison signal COMP1 to a set input S of a flip-flop 110 when the voltage Vosc on the capacitor C-osc is lower than a lower limit VREF1
Data Source
AI summary
A frequency jittering circuit modulates a hysteretic band of an oscillator such that the clock generated by the oscillator has a jitter frequency, and thus a switching mode power supply operative on the clock will have a jittering switching frequency.