Three design tips for power converters

Designing a power converter requires three key elements when producing a quality product. A power converter needs component de-rating, calculation for the power factor, and EMI/EMC (electromagnetic interference/compatibility). Without these requirements, the design may not work at all.

De-rate components is one of the most common steps in power converter designs. Engineers often stop after looking at the component tolerance once the converter works. They forget that the component value listed in the datasheet usually applies to one specific set of operating conditions that don’t match their own. For example, the capacitance of a ceramic chip capacitor, with a tolerance of +/-20%, will drop as the dc voltage applied to it increases. The capacitance could be 80% less than expected if operating near the rated voltage.  If this has not been taken into account the power supply may not meet all of the design requirements or may not work at all.

The power factor of a converter is another important element in designing power converters. In ac-dc power supply designs, engineers will sometimes forget to account for the power factor. It usually occurs because engineers calculate the Real Power, rather than the Apparent Power, and use this to determine the input current. A low power factor means that the system will draw more current than the engineer has estimated. This can cause more heat to be generated, shortening the life of and/or damaging the converter.

Lastly, consider the electromagnetic interference/compatibility (EMI/EMC) of the product.   EMI/EMC can be frustrating for power supply design engineers.  Many of the causes of EMI/EMC problems do not appear on the schematic but are the result of the PCB layout.  Switching power supplies are inherently noisy devices and if EMI/EMC is not considered when placing and routing components, there is a good chance the supply will not meet the required EMC standards.

Good luck on designing your power converters.

Special thanks to CUI, Inc.