Frequency Jittering Control Circuit for Power Supply EMI Reduction
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Solution Overview
Problem
Conventional power supply apparatuses face challenges in improving electro-magnetic interference (EMI) characteristics, as EMI generated is often concentrated at integer multiples of the switching frequency, leading to larger EMI filtering devices and increased manufacturing costs, and variable-frequency modes fail to adjust effectively to real input/output conditions.
Innovation Solution
A frequency jittering control circuit and method that introduce low-frequency disturbances into feedback circuits to jitter the switching frequency within a predetermined range, dispersing EMI and improving EMI performance even when input voltage is constant, using a frequency jittering signal generated by a frequency jittering circuit, feedback compensation circuit, and control circuit to adjust the main switch in the power supply apparatus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant frequency operation is used, then control is simple, but EMI characteristics deteriorate and filtering device size increases
Solution Approach 1:
The patent applies dynamics by transforming the constant switching frequency into a variable frequency that fluctuates within a predetermined range. The frequency modulation circuit modulates the switching frequency based on a sine wave signal, making the frequency dynamic rather than static. This resolves the contradiction by allowing simple control architecture while achieving better EMI characteristics through frequency variation.
Solution Approach 2:
The patent changes the frequency parameter of the switching signal from constant to variable. By introducing a frequency modulation circuit that varies the switching frequency within a predetermined range (e.g., 65kHz-75kHz for a 70kHz nominal frequency), the system achieves improved EMI characteristics without significantly increasing control complexity.
2Object-generated harmful factors
If variable-frequency control is used, then EMI characteristics improve, but the frequency changes depend on restriction conditions and cannot adjust effectively to real input/output conditions
Solution Approach 1:
The patent implements feedback by detecting the actual output voltage and comparing it with the reference voltage. The error signal from this comparison is fed back to the frequency modulation circuit, which adjusts the switching frequency accordingly. This closed-loop feedback mechanism enables the system to adapt to real input/output conditions while maintaining improved EMI characteristics through frequency variation.
Solution Approach 2:
The system performs self-adjustment by using its own output detection to automatically modulate the switching frequency. The frequency modulation circuit responds to detected output conditions and self-regulates the frequency without requiring external intervention, achieving both improved EMI characteristics and adaptability to real conditions.
3Object-generated harmful factors
If larger EMI filtering devices are used, then EMI characteristics improve, but manufacturing cost increases
Solution Approach 1:
The patent replaces the mechanical approach of using larger physical filtering components with an electronic approach of frequency modulation. By varying the switching frequency within a predetermined range, the system achieves better EMI characteristics without requiring larger or more complex filtering hardware, thereby reducing manufacturing costs while maintaining or improving EMI performance.
Data Source
AI summary
A frequency jittering control circuit includes a frequency jittering circuit, a feedback compensation circuit, a comparator and a control circuit. The frequency jittering circuit generates a frequency jittering signal. The feedback compensation circuit generates a feedback compensation signal in response to the frequency jittering signal and an output signal. The comparator outputs a comparison output signal according to the feedback compensation signal and an oscillation signal. The control circuit outputs a frequency jittering control signal for switching a main switch in a power supply apparatus, according to the comparison output signal, such that the power supply apparatus correspondingly generates the output signal.