How to attenuate noise in industrial servo rectifier circuits?

The noise in the servo rectifier circuit is mainly caused by diode reverse recovery and power grid harmonics, manifesting as excessive conducted interference in the low-frequency range (150kHz-1MHz). Attenuating this type of noise requires a multi-stage filtering strategy. The solution from Etymotic is as follows: a CMZ7060A-701T common-mode inductor (70μH) is installed at the rectifier bridge output to suppress common-mode noise, while two sets of capacitors are connected in parallel: a 470μF/400V electrolytic capacitor to handle low-frequency ripple, and a 100nF/630V C0G ceramic capacitor to filter high-frequency noise.

On the AC input side, a PBZ3216E-600Z0T ferrite bead (600Ω@100MHz) is connected in series with two capacitors (0.47μF/305VAC) to form a differential-mode filter. To further protect against power grid surges, an SMDJ36CA TVS diode can be used. Test data shows that this filtering network can attenuate conducted interference in the rectifier circuit by more than 25dB, meeting the CISPR 11 Group 1 Class A limits. When laying out the circuit, the rectifier bridge heatsink must be properly grounded, and the filter capacitor should be placed as close as possible to the rectifier tube pins.