Active EMI Filter for Switching Power Supply Ripple Elimination
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Solution Overview
Problem
Switching power supplies face challenges in miniaturization due to the need for large inductive components in passive EMI filters, which are required to prevent high frequency harmonic pollution, and existing solutions fail to effectively eliminate switching frequency ripples, leading to electromagnetic interference.
Innovation Solution
An active EMI filter is implemented, using an input capacitor and a transistor controlled by a feedback circuit to dynamically regulate the voltage and eliminate switching frequency ripples, reducing the need for large passive components and allowing for miniaturization while preventing harmonic pollution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive EMI filters with large inductive components are used, then high frequency harmonic pollution is prevented, but the switching power supply cannot be miniaturized
Solution Approach 1:
The patent replaces the traditional passive mechanical/physical EMI filter (inductors and capacitors) with an active electronic filtering system using a transistor switch and control circuit. This substitution eliminates the need for large inductive components while maintaining EMI suppression functionality through active switching and feedback control.
Solution Approach 2:
The invention changes the operating parameters by using high-frequency switching of the transistor controlled by PWM signals, transforming the EMI filtering approach from passive low-frequency operation to active high-frequency operation. This parameter change enables effective EMI suppression without requiring large physical components.
2Object-affected harmful factors
If passive EMI filters are used, then electromagnetic interference is reduced, but switching frequency ripples cannot be effectively eliminated
Solution Approach 1:
The patent implements a feedback control mechanism where the control circuit monitors the switching frequency ripples and dynamically adjusts the transistor switching timing and duty cycle to actively cancel out the ripples. This closed-loop feedback system effectively eliminates switching frequency ripples that passive filters cannot address.
Solution Approach 2:
The invention transitions from static passive filtering to dynamic active filtering by using a transistor switch that can rapidly change its state in response to switching frequency ripples. The dynamic switching and control enable real-time adaptation to eliminate ripples across varying operating conditions.
3Object-affected harmful factors
If large inductive components are used in EMI filters, then harmonic pollution is prevented, but circuit area increases
Solution Approach 1:
The patent replaces large physical inductive components with an active transistor-based switching circuit that provides equivalent or superior EMI suppression functionality. This substitution dramatically reduces the circuit area occupied by EMI filtering components while maintaining or improving harmonic pollution prevention.
Solution Approach 2:
The transistor switch and control circuit serve multiple functions simultaneously: they act as the main power switching element, provide EMI filtering, and enable ripple elimination through feedback control. This multi-functionality consolidates what would traditionally require separate large inductive components into a compact integrated solution.
Data Source
AI summary
An EMI filter configured for an AC-DC switching power supply, and that is coupled between a DC-DC converter and a rectifier circuit that receives an AC power supply, can include: an input capacitor coupled in parallel to input terminals of the DC-DC converter; a transistor having a first terminal coupled to a first terminal of the input capacitor, and a second terminal coupled to ground; and a control circuit configured to generate a control signal that controls the transistor according to a feedback voltage that represents ripple information of an input voltage to the DC-DC converter, and at least one of a current that flows through the transistor, and a voltage at the first terminal of the transistor, where the control signal is used to regulate the voltage at the first terminal of the transistor to substantially eliminate switching frequency ripples from an input current of the DC-DC converter.