Frequency Modulation Device for Switching Mode Power Supply EMI Reduction
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Solution Overview
Problem
Switching mode power supplies (SMPS) generate switching noise that causes electro-magnetic interference (EMI), leading to operational disturbances in peripheral devices, and existing solutions to mitigate this issue, such as using filters, increase production costs.
Innovation Solution
A frequency modulation device comprising a counter, latch unit, reference signal generator, and PWM oscillator that generates an oscillator signal with varying slopes, allowing for irregular modulation of the operational frequency to reduce EMI by synchronizing with the switching operation of the SMPS, thereby minimizing harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filters are added to the SMPS to prevent EMI, then EMI protection is improved, but production cost increases
Solution Approach 1:
The patent converts the harmful switching noise into a beneficial frequency modulation signal. The switching noise characteristics are captured and transformed into a modulation waveform that irregularly varies the operating frequency, thereby dispersing harmonic energy and reducing EMI without requiring additional filtering components.
Solution Approach 2:
The patent changes the operating frequency parameter dynamically by modulating it with the switching noise-derived waveform. This causes the switching frequency to vary irregularly over time, spreading the harmonic spectrum and reducing peak EMI emissions, thus eliminating the need for costly filters.
2Stability of the object's composition
If the switching frequency is kept constant for stable operation, then operational stability is improved, but EMI increases due to fixed harmonics
Solution Approach 1:
The patent introduces dynamics into the previously static switching frequency. By modulating the frequency with the switching noise waveform, the operating point becomes time-variant while maintaining system stability. This dynamic frequency adjustment disperses harmonic energy across a broader spectrum, reducing concentrated EMI emissions.
Solution Approach 2:
The patent employs periodic modulation of the switching frequency using the switching noise itself as the modulation source. This periodic variation in frequency creates a spreading effect on the harmonic spectrum, reducing peak EMI while maintaining overall operational stability through controlled frequency excursions.
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 frequency modulation device effectively reduces EMI by continuously varying the switching frequency, minimizing harmonic interference and reducing the need for additional filtering devices, thus lowering production costs and improving operational stability of SMPS.
Implementation Method 1
The PWM oscillator includes a capacitor, a first comparator for comparing the first reference signal and the oscillator signal, a second comparator for comparing the second reference signal and the oscillator signal, a source-current source for charging the capacitor, a sync-current source for discharging the capacitor
Data Source
AI summary
The present invention relates to a frequency modulation device and a switching mode power supply using the frequency modulation device. To prevent electro-magnetic interference (EMI), it is required to slightly vary a switching operation frequency in an SMPS operation. In some embodiments, at least one first signal having a predetermined cycle is generated, a second signal corresponding to a level of a first signal is generated at a turn-off time of a switch, a first reference voltage having at least two different levels is generated according to the second signal, and an oscillator signal for increasing along a first slope during a first period and decreasing along a second slope during a second period between the first reference voltage and a second reference voltage having a level that is different from the first reference voltage is generated.