How to stabilize EMC with wide voltage input in EPS?

When an EPS has a wide input voltage range (e.g., AC85-305V), to ensure stable EMC performance across the entire input range, the following design considerations should be taken into account:

1. Input filter parameter stability: The impedance characteristics of the input EMI filter components (especially the common-mode inductor) should not change drastically across the entire voltage and current range. Attention should be paid to whether the inductor saturates at the minimum input voltage (maximum input current).

2. Impact of variable parameter control: To accommodate wide input voltages, the pre-amplifier PFC or DC-DC circuit may employ frequency conversion or variable mode control, which alters the spectral distribution of switching noise. It is necessary to ensure that the noise spectrum is effectively covered by the filter in all operating modes.

3. Operating point of protection devices: The clamping voltage of protection devices such as varistors (MOVs) at the input terminal must adapt to the highest input voltage, and the impact of their parasitic capacitance on EMI must be considered during filter design.

4. Auxiliary power supply stability: The auxiliary power supply powering the control circuit must also operate stably over a wide input range, and its own EMI should not change significantly with the input voltage. EMC verification must be performed under the most stringent input conditions (typically low voltage and high current) during design.