TDK Corporation Inductors and Coils

TDK offers a comprehensive range of inductors for diverse applications. Power inductors for DC-DC converters include shielded and unshielded types with ferrite or metal composite cores, inductance values from sub-microhenry to millihenry, and current ratings from milliamps to over 100A. Common mode chokes are available in toroidal and bobbin constructions for EMI suppression on power lines and data interfaces. High-frequency coils for RF applications include air-core and ferrite-core inductors with high Q factors. TDK also offers specialized inductors for automotive applications (AEC-Q200 qualified), coupled inductors for SEPIC and flyback converters, and current sense transformers. The product range covers surface-mount sizes from 0603 to large through-hole types for high-current applications.

Select based on application type: power inductors for DC-DC, common mode chokes for EMI, high-frequency coils for RF.

Ferrite and metal composite (powdered iron) cores offer different characteristics for power inductors. Ferrite cores provide high permeability and low core losses at high frequencies, making them ideal for switching frequencies above 500kHz. They have sharp saturation characteristics - inductance drops rapidly when saturation current is exceeded. Metal composite cores offer softer saturation with gradual inductance reduction, providing better handling of transient currents. They have higher saturation flux density, allowing more energy storage in the same volume. However, metal composite cores have higher core losses, making them better suited for frequencies below 500kHz. Ferrite inductors are typically more cost-effective, while metal composite inductors offer better current handling and transient response.

Choose ferrite for high-frequency, cost-sensitive applications; select metal composite for high-current or soft saturation requirements.

Selecting inductors for DC-DC converters requires calculating the required inductance based on switching frequency, input/output voltages, and allowable ripple current. The basic formula is: L = (V_in - V_out) × D / (f_sw × ΔI_L), where D is duty cycle, f_sw is switching frequency, and ΔI_L is inductor ripple current (typically 20-40% of DC current). Next, verify the saturation current rating exceeds the peak inductor current (I_DC + ΔI_L/2). Check that the RMS current rating handles the thermal requirements. Consider DCR for efficiency calculations - lower DCR means less conduction loss. For EMI-sensitive applications, choose shielded inductors. TDK provides online tools and application support to help with inductor selection.

Calculate inductance based on ripple current requirements; verify saturation and thermal ratings.

Inductor saturation occurs when the magnetic core material reaches its maximum flux density and can no longer support increased magnetic field. When saturation occurs, inductance drops dramatically (often to 10-20% of nominal value), causing increased ripple current, higher losses, and potential converter instability. The saturation current (Isat) is specified as the current at which inductance drops by a certain percentage, typically 30%. It's crucial to ensure the peak inductor current in operation never exceeds Isat. For ferrite inductors, saturation is abrupt and must be strictly avoided. Metal composite inductors have softer saturation characteristics, providing more margin. Temperature affects saturation - higher temperatures generally reduce saturation current.

Design with peak current well below saturation rating; consider temperature effects on saturation.

Common mode chokes are inductors designed to suppress common mode noise - electrical interference that appears equally on both lines of a differential pair relative to ground. They consist of two windings on a shared magnetic core, typically toroidal or U-core construction. When common mode currents flow in the same direction through both windings, they create additive magnetic flux that presents high impedance to common mode noise. For differential mode signals (currents flowing in opposite directions), the magnetic flux cancels, presenting minimal impedance to the desired signal. Common mode chokes are essential for EMI filtering in power supplies, data interfaces, and motor drives. TDK offers common mode chokes for various frequency ranges and current ratings.

Select common mode chokes based on frequency range of noise, current requirements, and required attenuation.