MID-PLN Planar Transformers Würth Elektronik Midcom MID-PLN Planar Transformers are optimized for 200kHz to 700kHz switching frequency and feature a 150W to 250W power range. These devices come in an ERI25/10/18 or ER19/4.8/15 package with a 2250VDC isolation voltage and an operating temperature range of -40°C to 125°C. Typical applications for Würth Midcom MID-PLN Planar Transformers include forward converters, half- or full-bridge converters, and active clamp topology.