January 2014

Power inductors for advanced engine management

Built tough for high temperatures

Engine control modules monitor and manage the operation of modern combustion engines in cars to boost energy efficiency. Mounted ever closer to the engine, they must withstand high temperatures and strong vibrations. TDK’s CLF-D series of power inductors are key components in the power supplies of such modules.

The engine control module (ECM) is one of dozens of electronic control units (ECUs) that manage the multitude of functions in a modern vehicle. The ECM is responsible for monitoring and controlling all of the processes in a combustion engine, from fuel injection and air intake to exhaust and cooling. The primary objective is to achieve optimal fuel efficiency and minimal exhaust gas emissions.

In order to reduce the weight of cars by keeping heavy wire harnesses as short as possible, automotive engineers have moved ECMs ever closer to the engine in recent years. When mounted directly on the engine, the ECMs (Figure 1) and their components must be designed to withstand extreme environmental temperatures and strong vibrations.

TDK has developed the new CLF-D series of SMD wirewound power inductors for applications in such extreme environments. Rated for operating temperatures from −40 °C to +150 °C, the new component is qualified to AEC-Q200, and thus meets the demanding requirements of the automotive industry.

Figure 1: Basic design and structure of an ECM

The TDK CLF-D power inductor is a key component in the DC-DC converter and helps ensure an efficient power supply in the ECM.

Step-down DC-DC converters for control ICs

The DC-DC converter in the ECM is a stepdown or buck converter. It converts the 12 V board voltage into stable DC voltages needed for the subsystems of the ECM. Depending on the IC, they range from 1.2 V to 5 V. Figure 2 shows the basic circuit of a step-down converter. Switching elements such as MOSFETs are connected to the circuit in series, and a direct current is turned on and off cyclically. One of the key components in the power supply is the power inductor, which stores and releases energy according to the duty ratio to ensure a constant flow of current. Together with a capacitor, the power inductor forms a smoothing circuit with the magnitude of output voltage determined by the duty ratio.

Figure 2: Basic circuit diagram of a step-down (buck) converter

The power inductor in a step-down converter fulfills two functions at the same time: storage of energy and smoothing of the output voltage.

Designed for fully automated manufacturing

In order to withstand the extreme environmental conditions encountered so close to the engine, the CLF-D series employs special heat-resistant materials throughout and a unique simplified structural design able to withstand strong vibrations.

The CLF-D series of power inductors consist of a ferrite drum core, around which the coil is wound (Figure 3). The coil is shielded by an octagonal ferrite core to prevent magnetic coupling with other electronic parts, which would cause interference and power losses. Thanks to their magnetic shielding, CLF-D series power inductors can be easily mounted in high densities and thus help downsize an ECM or other in-vehicle ECUs.

Moreover, the CLF-D series has no base, meaning it comprises fewer parts. To manufacture the wirewound SMD power inductor, TDK uses new automated machines for both the wirewinding and connecting processes and has introduced a design that needs no soldering. As a result, the CLF-D series is manufactured using a fully automated production process, which means extremely uniform high quality for the finished components.

Figure 3: Mechanical design of the TDK CLF-D series of power inductors

TDK’s CLF-D employs special heat-resistant materials and a simplified structural design that can withstand strong vibrations.

Outstanding and reliable performance

The new CLF-D series of power inductors is available for inductance values ranging from 1 μH to 470 μH and rated currents from 0.37 A to 8.9 A, depending on the type (Table). Thanks to their innovative design and rugged materials, the TDK power inductors are suitable for the most demanding automotive electronics applications. The main features and benefits are:

– Broad operating temperature range up to +150 °C thanks to heat-resistant materials

– Solder-free design

– Fully automated manufacturing process for consistently highest quality

– AEC-Q200 qualified

– RoHS-compatible and suitable for lead-free soldering

 

In addition to their reliable performance in ECMs, the CLF-D series is also suited for power supply circuits of other automotive ECUs, such as those for ABS systems, HID lamps, airbag systems and more.

Table: Key data for the TDK CLF-D series of power inductors

Dimensions [mm]6.9 x 7.2 x 4.5
Rated inductance [μH]1 to 470
DC resistance [Ω]0.0096 to 1.42
Rated current* IDC1 [A]

0.43 to 8.9

Rated current* IDC2 [A]

0.37 to 5.2

Operating temperature range [°C]

-40 to +150

* Rated current is the smaller value of IDC1 and IDC2

IDC1: Current at which inductance drops 10 % below the initial value due to DC superimposition

IDC2: Current at which the coil temperature increases by 30 °C

Figure 4: Inductance vs. frequency and DC current

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