Compact Coupled Inductors with High Saturation Current

The fields of application of dual inductors are diverse. They can be used as coupled inductors in various non-isolated DC/DC converter topologies or as transformers in flyback converters. A further application involves the use as common-mode inductors in power supply lines. TDK´s dual inductor series offer coupling factors up to 99%. The compact robust designs feature functional isolation voltages between the two windings up to 500 V.

Features

Electrical Characteristics

High rated currents up to 7.05 A
Exceptionally high saturation currents of up to 16.1 A
Very low RDC values as low as 0.018 Ω
High temperature range of up to 150 °C

Construction

Tight coupling of the 2 windings
Laser welded connection
Outstanding mechanical and thermal robustness

Flexible Usage

1:1 transformer
Two single inductors connected in series or parallel

Overview of Available Types

	Inductance (µH)	Saturation current (A)
12.5 x 12.5 x 10.5 mm	3.9 – 47 µH	4.7 – 16.1 A
12.5 x 12.5 x 8.5 mm	2.0 – 100 µH	2.2 – 15 A
10.4 x 10.4 x 6.3 mm	2.2 – 47 µH	1.71 – 6.17 A
7.3 x 7.3 x 4.8 mm	2.2 – 47 µH	1.1 – 5.6 A

DC/DC Converter Topologies

SEPIC

A SEPIC (Single-Ended Primary Inductance Converter) is particularly suitable for battery-powered devices or automotive applications. It provides a constant non-inverted output voltage that can be above or below the input voltage. This allows battery voltage fluctuations and different load scenarios to be compensated. This is possible because the SEPIC technology combines a boost and buck converter. Another significant advantage of this circuit topology is a constant input current, which in combination with the input filter consisting of C1 and L1 results in a considerably lower conducted interference. Using a coupled inductor can significantly reduce ripple current load and thus core losses. Although the coupling capacitor C2 provides some isolation between input and output, SEPIC is one of the non-isolated topologies.

ZETA

ZETA is another multiwinding converter topology which offers basically a similar functionality than a SEPIC. Both power converters are able to step up and down the input voltage and generate a stable non-inverting output voltage. Another similarity is the DC transfer function VOUT = VIN x D/(1-D). Due to the slightly rearranged circuit configuration with L2 and C3 at the output ZETA converters providing a continuous output current with a low ripple. Unlike a real buck-boost, ZETA converters just require one buck controller IC directly driving a MOSFET. The output is not isolated from the input.

CuK

CuK converters have like SEPIC and ZETA topologies the ability to regulate a voltage that is above or below the input voltage. A special feature, required by some applications, is an inverted output voltage. A major benefit from an EMI point of view is the continuous current flow in combination with the LC filters on both the input and output side of the converter. This provides a stable current drain from the battery and is significantly minimizing the ripple current. The output is not isolated from the input.

Flyback

Flyback converters are among the most commonly used topologies in industrial electronics and lower power automotive applications. They are extremely popular due to the relatively simple and thus cost-effective design of this circuit topology, which requires only a few components. The coupled inductor serves as a storage choke and also provides galvanic isolation between input and output. The energy transfer takes place during the off-time of the MOSFET. This topology can generate non-inverted output voltages far below or above the input voltage. Depending on the converter's isolation requirements or the safety standard applicable to the particular application, either a coupled inductor with a functional isolation of up to 500 V or a transformer can be used. Another special feature of flyback converters is the ability to generate multiple output voltages. A disadvantage of this topology are the high voltage peaks generated by the switching transistor. This can make an EMC filter necessary at the converter's input to suppress the conducted interference that occurs.

Multi-Output Buck

Coupled inductors can be also used to create an auxiliary or a second output voltage respectively by only using a single buck regulator. This can help to reduce the complexity of the circuits and thus save costs and space on the board.