TDK has introduced the EP21 series of flat-wire double chokes (ordering code B82552J*J021). The company intends them for common-mode filtering in DC-DC converters and other low-voltage EMC protection circuits.
The parts share a 23.8 x 17.7 mm footprint and stand 21.6 to 22.3 mm tall, depending on the version. The terminations sit under the body of the component, which TDK says minimizes the board space it occupies. The four-pin layout improves mechanical reliability, according to the company.
Rated voltage is 48 V AC or 80 V DC. Rated currents run from 20.3 to 35 A and need no derating up to 70° C. Above that temperature the parts must be derated.
Four versions make up the series, and inductance trades off against current rating across them. The 160 µH version carries 35 A at a DC resistance of 0.44 mΩ, and the 640 µH version carries 20.3 A at 1.75 mΩ. The two in between are rated at 280 µH and 30.8 A and at 440 µH and 23.5 A.
A common-mode choke winds two conductors so their magnetic fields cancel for the differential current the load draws but add for current flowing in the same direction on both lines. That lets the part impede common-mode noise while passing the supply current largely untouched. Stray inductance is the share of each winding's field that doesn't couple to the other winding, and it acts on the differential-mode current instead. Average stray inductance ranges from 200 to 900 nH, and maximum impedance occurs at frequencies between 500 kHz and 3 MHz, depending on the type.
The windings are flat wire on an MnZn ferrite core. Flat wire fills the winding window more completely than round wire, which lowers DC resistance for a given number of turns. Conduction loss rises with the square of the current, so DC resistance is a main driver of temperature rise at 35 A.
Source: TDK
