Switching frequency in Power Supply

Having a higher switching frequency helps in reducing size of components such as transformers and inductors and help achieve higher power density. A smaller size will typically also mean lower cost of the product and a smaller physical size of the product.

Having a higher switching frequency hurts by increasing switching losses, snubber losses and increasing EMI. Higher losses will also lead to lower efficiency. At higher frequencies, losses due to skin effect and proximity effect will require careful selection of winding structure, wire size etc., which is often a challenge for most engineers who have not studied the subject.

So choice of switching frequency is a tradeoff and general tendency is to keep the switching frequency low but this also results in a bulkier and expensive power supply.

Most EMI regulations require conducted EMI measurement from 150kHz to 30MHz and radiated EMI measurement for frequencies over 30MHz. This has led to increase of switching frequency but yet most designers will keep it lower than 150kHz so that the fundamental component of switching frequency is still below the EMI measurement range.