Active EMI Filter Damping Network to Prevent Op-Amp Saturation
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Solution Overview
Problem
Switched mode power supplies (SMPS) generate noise due to the switching of power transistors, which can manifest as electromagnetic interference (EMI) and affect the power source and other connected devices, leading to performance degradation and potential saturation of active electromagnetic interference filters (AEFs).
Innovation Solution
The implementation of an active electromagnetic interference filter (AEF) with a damping network that makes the AEF less capacitive, particularly at resonant frequencies, thereby reducing the noise current and preventing operational amplifier saturation. This is achieved by introducing a resistor or a combination of resistor and capacitor in the damping network to increase the phase angle of impedance, reducing the capacitive nature of the AEF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an active electromagnetic interference filter (AEF) is used to reduce noise, then electromagnetic interference is reduced, but the operational amplifier may become saturated due to noise current
Solution Approach 1:
A damping network is introduced as an intermediary component between the AEF output and the power source. This damping network, comprising a resistor and capacitor, mediates the interaction by reducing the noise current that would otherwise flow into the operational amplifier, thereby preventing saturation while maintaining the EMI filtering function.
Solution Approach 2:
The damping network changes the impedance parameters of the AEF output by introducing resistive and capacitive elements. This parameter modification reduces the capacitive nature of the AEF output, thereby reducing the noise current magnitude and preventing operational amplifier saturation.
2Reliability
If the AEF is made less capacitive to reduce noise current, then operational amplifier saturation is prevented, but the filter's capacitive filtering capability may be reduced
Solution Approach 1:
The filtering function is segmented into two parts: the AEF provides active filtering with cancellation capability, while the damping network provides passive damping and impedance matching. This segmentation allows each component to optimize its specific function without compromising the other.
Solution Approach 2:
The damping network acts as an intermediary that modifies the impedance characteristics between the AEF and the power source, allowing the AEF to maintain its capacitive filtering capability while the damping network reduces the noise current through impedance transformation.
3Reliability
If a damping network is added to the AEF, then noise current is reduced and operational amplifier saturation is prevented, but the device complexity increases
Solution Approach 1:
The damping network uses simple, inexpensive passive components (resistor and capacitor) that can be easily implemented without adding significant complexity. These components are readily available and require minimal design effort compared to more complex active circuits.
Data Source
AI summary
In some examples, a circuit includes an amplifier, a resistor, and a damping network. The amplifier has an amplifier output and first and second amplifier inputs. The first amplifier input is adapted to be coupled to a first terminal, and the second amplifier input is configured to receive a reference voltage. The resistor is coupled between the amplifier output and the first amplifier input. The damping network is coupled between the amplifier output and the first terminal.