Modern ICs for switched-mode power supply units and switching transistors allow for ever higher switching frequencies while keeping switching losses low thanks to steeper transition slopes. The increase in switching frequency enables the use of capacitors with low capacitance values and inductors with low inductance values. As electrical values decrease, so does the size of the components, which means less space taken up by the construction, less weight, and less cost for the circuit as a whole. And this also increases the power density of the circuit, which helps the components to contribute towards reducing the CO2 emission of the vehicle.
In order to achieve good efficiency, parasitic effects also need to be minimized despite miniaturization. In coils, direct current resistance (DCR) and effective resistance are the key factors here, accounting for the core losses in the equivalent circuit diagram. Vishay's IHLP® series is a range of miniaturized inductors with excellent electrical properties (see figure).
Core material for low eddy current losses
IHLP stands for "Inductor, High Current, Low Profile". The core in this case is not ferrite, but a compressed composite made of a soft magnetic iron powder with an epoxy resin used as a binder. The iron powders determine the magnetic properties. The composite is a poor electrical conductor that insulates the iron powder particles from one another, thus keeping eddy current losses low.
Increasing quality with superior EMC properties ...
During production of the component, a coated copper coil is brought into contact with a wire frame, embedded in a powder mixture in a press mold, and this mixture is then compressed into its form at a pressure of up to 2.8t/cm2. The resultant inductor coil unit provides a magnetic shielding effect and reduces interference from stray electromagnetic fields. This results in a compact high-performance inductor for surface-mounted devices that offers superb electromagnetic compatibility properties.
Typical applications for such inductors with compressed coil units include LED drivers, switched-mode power supply units, DC/DC converters and EM filters. They also meet special requirements by varying the mixture proportions of the composite, and by using different powder materials and grain sizes. Although the concept is already over 20 years old, Vishay continues to evolve the formula. Even today, new versions are being produced that are optimized for saturation (IHLP...Suffix A1), time constants (L/DCR), coil quality (IHLP...Suffix 1A) or operating temperature (IHLP...Suffix 5A, 8A).
... and specified for temperatures up to 180°C
For use in applications where environments are in play that demand high robustness with more stringent heat requirements, there are some inductors in the IHLP series that are specified for operating temperatures up to 180°C. This provides benefits in heat management or expands the potential uses to applications where actuators are located directly adjacently to the vehicle component to be controlled. The inductor's FIT value (failure in time) falls, and its service life increases.
More features of IHLP inductors:
Optimum proportion of direct current resistance (DCR) and inductance (L) to housing size (large τ=L/DCR).
Within the operating range, the dependency of inductance L on a superimposed direct current is relatively low, so the differential permeability μr,diff = dH/dB is almost constant. This makes IHLP inductors especially suitable for use in switched-mode power supply units and as filter components in power supply units.
The dependency of these inductors on temperature is low compared to other core materials.
The saturation field strength has comparatively little dependency on temperature.
To help developers in their use of inductors, Vishay offers the "IHLP Inductor Loss Calculator Tool" (www.vishay.com/inductors/calculator/calculator), which supports boost, buck and buck-boost switched-mode power supply topologies. 3D models of inductors are available for virtual models of assembled PCBs. Equivalent circuit diagrams are also available on request from Vishay for electrical simulations.
Find components at www.rutronik24.com.
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