DC-DC Power Supply Frequency Modulation for EMC Noise Suppression
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Solution Overview
Problem
In-vehicle electronic equipment experiences electromagnetic compatibility (EMC) issues due to radiation noise emitted from switching power supplies, which do not meet CISPR 25 standards, primarily because the current flowing in power supply cables drastically changes during switching operations.
Innovation Solution
A direct current power supply apparatus is designed with a current stabilizing circuit connected before or after the DC-DC converter, incorporating a variable frequency oscillating circuit and oscillating control circuit to manage the switching frequency, and a spectrum diffusion function to distribute electromagnetic noise across a broader frequency band, thereby reducing peak values and meeting EMC standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a switching power supply (DC-DC converter) is used to convert direct current voltage, then power supply efficiency is improved and voltage decrease is prevented, but electromagnetic radiation noise is emitted and conducted noise rides on the power supply cable
Solution Approach 1:
The patent applies spectrum diffusion by modulating the switching frequency of the DC-DC converter to vary slightly over time, transforming the concentrated narrowband noise into distributed wideband noise. This frequency parameter change ensures that the total noise energy remains constant while the peak spectral density is reduced, maintaining power conversion efficiency while improving electromagnetic compatibility
Solution Approach 2:
The patent introduces a current stabilizing circuit as an intermediary component between the power supply cable and the DC-DC converter. This circuit stabilizes the input current to the converter, preventing drastic current changes during switching operations that cause radiation noise, thereby reducing conducted and radiated electromagnetic interference while preserving the efficient voltage conversion function
2Object-generated harmful factors
If the current flowing in the power supply cable is stabilized, then radiation noise is reduced, but the switching operation capability of the power supply apparatus is affected
Solution Approach 1:
The current stabilizing circuit applies partial stabilization by smoothing only the high-frequency switching ripple components of the input current while preserving the essential switching operation characteristics. This selective filtering approach reduces radiation noise caused by drastic current changes without interfering with the normal switching function and power conversion capability of the DC-DC converter
Solution Approach 2:
The patent employs dynamic frequency modulation in the spectrum diffusion technique, where the switching frequency is varied within a certain range rather than maintained at a fixed value. This dynamic approach distributes noise energy across a broader frequency spectrum, reducing peak radiation while maintaining the switching converter's operational effectiveness and adaptability to varying load conditions
3Object-generated harmful factors
If spectrum diffusion function is provided to distribute electromagnetic noise energy, then peak noise values are suppressed, but device complexity increases
Solution Approach 1:
The patent combines the spectrum diffusion function with the existing oscillating circuit of the DC-DC converter by modifying the oscillation frequency control. Instead of adding a completely separate noise reduction system, the frequency modulation for spectrum diffusion is integrated into the converter's control architecture, sharing common components and control logic, thereby reducing overall device complexity while achieving noise suppression
Data Source
AI summary
A direct current power supply apparatus that converts direct current input voltage supplied from a direct current power supply and that outputs a direct current voltage at a different potential is shown. The apparatus includes a switching power supply apparatus and a current stabilizing circuit connected at a stage before or after the switching power supply apparatus. The switching power supply apparatus includes, an oscillating circuit in which a frequency is variable and that generates an oscillating signal to apply a switching frequency, and an oscillating control circuit that generates an oscillating control voltage or an oscillating control current that changes the frequency of the oscillating circuit to the frequency longer than the switching frequency.