Differential-mode (DM) interference in switching power supplies occurs when unequal currents flow in opposite directions through the power supply’s input or output lines, caused by fast switching of transistors (leading to voltage spikes and current ripples) and mismatched components in the power path. Effective DM interference handling requires targeted design strategies to attenuate noise at its source and prevent propagation to sensitive loads.

First, implementing DM filters is a primary method. DM filters typically consist of a series inductor (differential inductor) and a shunt capacitor (X capacitor), forming an LC low-pass filter. The differential inductor presents high impedance to DM noise (which flows in opposite directions through its two windings, generating additive magnetic fields that enhance inductance) while allowing low-frequency power signals to pass. X capacitors (connected between live and neutral lines in AC-DC SPS, or positive and negative lines in DC-DC SPS) shunt high-frequency DM noise to the opposite line, attenuating noise by 15–30 dB at frequencies from 1 MHz to 1 GHz. Selecting inductors with high Q-factor (to minimize insertion loss at power frequencies) and X capacitors with high voltage rating (matching the SPS’s input/output voltage) ensures filter effectiveness and reliability.

Second, optimizing the switching topology and control strategy reduces DM noise at the source. Soft-switching topologies (e.g., ZVS-ZCS converters, LLC resonant converters) minimize voltage and current spikes during transistor switching by ensuring zero voltage or zero current switching, reducing DM noise amplitude by 30–50% compared to hard-switching topologies (e.g., buck converters). Additionally, using current-mode control (instead of voltage-mode control) provides faster transient response, reducing current ripples (a major source of DM noise) by regulating the inductor current directly.

Third, component selection and matching are critical. Mismatched components (e.g., capacitors with different capacitance values, inductors with unequal inductance) can create imbalances in the power path, increasing DM noise. Using high-tolerance components (e.g., capacitors with ±5% tolerance, inductors with ±10% tolerance) and matching component parameters in the input/output stages minimizes these imbalances. Additionally, selecting low-ESR (equivalent series resistance) capacitors (e.g., ceramic or polymer capacitors) reduces voltage ripple, as ESR contributes to DM noise at high frequencies.

Fourth, optimizing PCB layout reduces DM noise coupling. This includes keeping power traces short and wide to minimize parasitic resistance and inductance (which amplify current ripples), separating power and signal traces to prevent noise coupling, and placing DM filters close to the switching components (e.g., MOSFETs, diodes) to block noise before it propagates to the input/output lines. Using a ground plane with minimal discontinuities also provides a low-impedance return path for DM currents, reducing noise radiation.

Combining these methods ensures that DM interference is suppressed to levels compliant with EMC standards, protecting sensitive electronic equipment connected to the SPS.

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