These Inductors and Magnetic Chokes Target Automotive Applications

By Murray Slovick, Contributing Editor
[Sponsored by Coilcraft]

Components that can handle complex and rugged HEV/EV environments are in higher-than-ever demand. What specs should designers focus on when designing on-board chargers and start/stop systems?

In the automotive industry, AEC-Q200-certified components perform a wide variety of tasks ranging from powertrain and transmission control to ABS braking and radar- and camera-based driver-assistance systems (Fig. 1). Here we will focus on three automotive applications that illustrate the level of performance required and the severe environmental conditions under which automotive power inductors and magnetic chokes must function:

  • As critical elements of on-board chargers (OBCs)
  • In start-stop systems
  • In suppression of EMI noise that easily occurs in cables

Multiple systems in electric vehicles require AEC-Q200-certified components. (Source: Coilcraft)

An OBC charges the batteries in a hybrid electric vehicle or electric vehicle (HEV/EV) by connecting the vehicle to the grid, which is the electric power source. The OBC provides the means to recharge the battery either at home or from outlets found in private or public charging stations. A typical OBC subsystem comprises two stages: an ac-dc stage with active power factor correction (PFC) and a dc-dc converter stage. Inductors are used in both the PFC converter and dc-dc converter section.

A common electronic architecture for an OBC is the inductor-inductor-capacitor (LLC) resonant topology. An LLC is suitable for OBC applications since the output voltage should be adapted according to the battery-charging voltage range and voltage can be adjusted with the switching frequency. Efficiencies up to 98% can be achieved with LLC converters.

Selecting the Best Inductor for your DC-DC Converter

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Proper inductor selection requires a good understanding of inductor performance and of how desired in-circuit performance relates to the information available in supplier data sheets. This article walks both the experienced power conversion specialist and nonspecialist through the inductor catalog and the important specifications.

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Comparing Components
One of the key design tasks after deciding on a circuit topology is component selection. The task for the designer is to go from knowing the desired inductance value to selecting an available component to do the job.

Inductors that can be used in dc-dc converters come in a wide variety of shapes and sizes and need to be carefully selected. Among key considerations are inductance (obviously), current saturation, dc resistance (DCR, the resistance in a compo­nent due to the length and diameter of the winding wire used), current rating, maximum operating temperature, electromagnetic interference (EMI), and efficiency at specific operating conditions. Even the inductance value must be looked at carefully as inductance itself depends on frequency, temperature, and current.

Current rating is the maximum current that the gauge of wire used in the inductor can handle at the rated temperature range. The hard part here is that current through a dc-dc converter inductor is always changing throughout the switching cycle and may change from cycle to cycle depending on converter operation, includ­ing temporary transients or spikes due to load or line changes.

Saturation, which must be avoided at the peak current, also can be variable as the limit reduces with temperature. Saturation current is the point where the magnetic field no longer increases proportionally with an increase in current—the core is said to become “saturated.” When current peaks reach saturation levels, the inductor starts to get hot.

One DC-DC Option
An attractive solution for dc-dc converters is Coilcraft’s XGL4020. It has the industry’s lowest dc losses, according to the company, and extremely low ac losses for a wide range of dc-dc converters. The device is available in 12 inductance values from 0.33 to 8.2 µH, with current ratings up to 15.2 A and soft saturation characteristics.

Coilcraft says it features the lowest dc resistance currently available in the market—up to 45% lower than its next-lowest soft-saturation products. XGL4020 Series inductors are qualified to AEC-Q200 Grade 1 standards with a maximum part temperature of +165°C, and they exhibit no thermal aging issues.

Solution for Stop/Start
As its name implies, a stop/start system shuts off the engine when it isn’t needed instead of letting it idle at a stop, and then rapidly restarts the engine when the driver accelerates. The dc-dc conversion becomes more complicated in these systems since the voltage level in start-stop isn’t inherently consistent.

One key solution lies in the advances achieved in high-current inductor technologies. In this regard, automotive designers would be well-served with Coilcraft’s AGP4233 series of shielded power inductors. With a combination of high current handling and high inductance, they’re nicely suited for start-stop systems. Offered in 12 standard inductance values from 6.8 to 470 µH, with current ratings as high as 101.8 A (custom values are also available), the AGP4233 series meets AEC-Q200 Grade 1 standards (−40 to 125°C), which measures its ability to withstand the temperature and physical stresses of automotive environments.

Chokes for Noise
The interior of an automobile is a noisy environment due to the strong magnetic fields induced in cables carrying large currents. These cables can function as antennas that radiate or pick up noise. It’s led to a requirement for common-mode filters to be used at the connector parts of the interfaces.

 Common-mode chokes are the most frequently used filter component to provide noise suppression on, for example, CAN (1 Mb/s) or CAN FD (5 Mb/s) data lines. A common-mode choke blocks high-frequency noise common to data or power lines while allowing the desired dc or low-frequency signal to pass.

The 1812 CANBUS choke is designed for common-mode noise suppression on CAN or CAN FD in automotive applications. (Source: Coilcraft)

Measuring just 4.95 × 3.18 × 3.0 mm, the AEC-Q200 Grade 1 Coilcraft 1812CAN Series offers inductance values from 11 to 100 µH to filter a broad range of common-mode noise frequencies with high attenuation (Fig. 2). It features up to 60% lower DCR than other CAN bus chokes, says Coilcraft, resulting in much lower losses on differential signal lines.

As with all Coilcraft products, complete technical specifications and free evaluation samples for the parts mentioned in this article are available at www.coilcraft.com.

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