How to control differential-mode conducted interference in an electrical force measurement switch (PMS)?

Differential-mode conducted interference in PMS primarily exists between power lines, originating from the rectifier loop of the switching power supply, the freewheeling loop of the Buck/Boost circuit, and the rapid current switching of digital circuits. This noise can be directly injected into the power grid along the power lines, causing conducted emission tests to exceed limits. The key to control this is reducing the intensity of the noise source and blocking its propagation path. In circuit design, adding a DSNubber circuit (such as a 1nF capacitor in series with a 2.2Ω resistor) to the source of the switching transistor or the freewheeling diode can slow down the rate of current change.

At the power input, a differential-mode filter network must be configured, for example, using a PBZ3216E120Z0T power inductor (12μH) as a differential-mode choke, forming an LC filter with an X2 safety capacitor (such as a 0.1μF/275VAC) to attenuate the 150kHz-30MHz frequency band. PCB layout must ensure that the power loop area is minimized, especially the hot loop formed by the input capacitor, switching transistor, and inductor. Meanwhile, ES series ultrafast recovery diodes (such as ES1A, trr=35ns) are selected for the DC/DC chip of the auxiliary power supply to reduce spikes caused by reverse recovery. Through comprehensive design, the differential mode conducted interference level can be controlled within 10dB margin below the EN 55032 Class A limit and pass the IEC 61000-4-6 conducted immunity test.