How to isolate EMI in the auxiliary power supply of frequency converter

To isolate the EMI of the auxiliary power supply of the frequency converter and prevent it from interfering with the control circuit, a combination of electrical and spatial isolation is required. The auxiliary power supply typically powers the control board, drive circuits, fans, etc., and its flyback or forward topology is itself a noise source. First, select an isolation transformer with an internal shielding layer, and ground the shielding layer to block common-mode noise coupled through parasitic capacitance between the primary and secondary sides. Filter circuits should be installed at both the primary input and secondary output of the auxiliary power supply. Small-sized common-mode inductors, such as the CMZ1608 series, and Y capacitors can be used on the primary side; π-type LC filters should be used on the secondary side.

The auxiliary power supply module should be placed in a separate area on the power board, preferably completely shielded with a metal shield, which should be connected to the main heat dissipation ground or the chassis. The connection points between the auxiliary power supply's ground wire and the power ground and signal ground must be carefully designed, usually using a single-point connection to prevent noise propagation through the ground wire. When powering sensitive control circuits, a linear regulator or high-performance DC-DC filter can be added after the auxiliary power supply output. Measure the output ripple and noise of the auxiliary power supply using an oscilloscope to ensure they are within the range required by the control circuit. Eintech's isolation transformers and filtering devices offer a reliable option for building low-noise auxiliary power supply systems.