The 200 W common mode filter CMF200 from Elec‑Con, a development house for customer-specific power electronics up to 1 kVA, is not much bigger than a matchbox. The heart of the system is a current-compensated choke, which reliably keeps annoying common mode interference from switching power supplies away from sensitive electronics such as panel and box PCs. In the sensitive frequency range 20…50 MHz, the attenuation is up to 20 dB.
The common mode filter CMF200 is designed for operating voltages up to 50 VDC and continuous currents up to 4 A (peak current 6 A). Customer-specific filter characteristics are possible, as is an adapted current carrying capacity. A reverse polarity protection that responds within 25 ns is conveniently integrated to effectively prevent damage to the downstream application.
The CMF200 can be used without cooling and without derating in the temperature range of -10°…+70° C. Even at 100% load, the MTBF is over 200,000 hours (almost 23 years of continuous operation); at 80% load, it is more than 300,000 hours according to SN 29500. The filter, which is only 50 x 44 x 18 mm in size, is built on a circuit board in accordance with UL94V-0.

Elec-Con has its own pre-compliance EMC laboratory and many years of experience in compensating conducted and radiated interference. Well-known customers also use this option of being able to check the EMC behavior of a circuit quickly and inexpensively.

Common-mode interference is caused by clocked power switches, for example in a switching power supply. The corresponding interference currents flow in the same direction on the forward and return conductors, and from there back via the parasitic capacitances via PE. This creates large, current-carrying loops, which often cause problems in EMC tests. Due to their frequency spectrum, common-mode interference can also throw industrial PCs out of sync – even leading to inexplicable system crashes.