EMI Reduction in Frequency-Modulated DC-DC Converters
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Solution Overview
Problem
Frequency-modulated switching mode power supplies face challenges in reducing average electromagnetic interference (EMI) noise, as direct switching frequency modulation is not suitable, leading to increased requirements for EMI filters and power loss.
Innovation Solution
A pre-regulator is used to vary the input voltage of a frequency-modulated converter, allowing the converter to change its switching frequency through a feedback control loop, thereby stabilizing the output voltage and spreading the switching noise spectrum to reduce average EMI noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If direct switching frequency modulation is applied to frequency-modulated converters, then EMI noise reduction is achieved, but the converter cannot maintain stable output voltage and requires larger EMI filters
Solution Approach 1:
The system is divided into two independent control loops: an inner loop that regulates input voltage to a pre-regulator and an outer loop that controls output voltage. This segmentation allows frequency modulation to be achieved through input voltage regulation without compromising output stability, resolving the contradiction between EMI reduction and reliable operation.
Solution Approach 2:
A feedback control mechanism is implemented where the pre-regulator adjusts input voltage based on frequency modulation requirements, and the DC-DC converter adjusts switching frequency based on output voltage feedback. This dual feedback system enables both EMI noise reduction through frequency spreading and maintained output voltage stability.
2Object-generated harmful factors
If direct switching frequency modulation is used, then EMI noise is reduced, but EMI filter size and power loss increase
Solution Approach 1:
Frequency modulation is achieved preliminarily through input voltage regulation before the main DC-DC conversion stage. The pre-regulator performs the frequency modulation function by varying input voltage, which allows the main converter to operate with more stable characteristics, reducing the burden on EMI filters and minimizing power loss while still achieving EMI noise reduction.
Data Source
AI summary
A method for reducing EMI for a frequency-modulated DC-DC converter includes pre-regulating an input voltage of the frequency-modulated DC-DC converter, so that the frequency-modulated DC-DC converter changes an operating frequency of the frequency-modulated DC-DC converter to stabilize an output voltage of the frequency-modulated DC-DC converter, so as to achieve a desired frequency extension.