RF Inductors - DeMint Components

Technical Application Notes
General Information

Technical Application Notes For Inductors And Chokes

Selecting The Optimum Indcutor Choke to Best Match The Right Performance:

Inductive components store energy intermittently in switch-mode power supplies and DC/DC converters, form parts of RF circuits or RFID systems, transform current/voltage, match impedances, are filter elements and last but not least interference suppression components to ensure EMC.

The requirements on inductors depend on how and where they are used. RF circuits need coils with high quality factors and resonant frequencies. EMC applications require high inductance to achieve good interference suppression characteristics, low Q factors being more desirable here due to the need to avoid resonance.

DeMint Electronics provides suitable inductive components for all applications. This quide contains a wide selection of standard components, from SMT types through high current inductors for power electronics applications to transformers.

Comparision of Inductor Factors for Applications
Applications	Inductance	Current Rating	Resonance frequency	Q factor	DC Resistance
RF Circuits, Resonant Circuits	low	low	very high	very high	low
EMC	high	high	high	low	very low
RFID	depends on the specific application	low	high	high	low
DC/DC Converters	depends on the specific application	high	medium	high	low
Transformers in DC/DC	depends on the specific application	depends on the specific application	medium	depends on the specific application	low
Signal Processing	depends on the specific application	low	high	-	medium

RF Circuits:

The DeMint RF product range of SMT and leaded RF chokes are especially suitable for RF and other high frequency circuits. Typical applications are resonant circuits and frequency-selective filters of the type increasingly used in telecommunications engineering and automotive electronics.

Filter Circuits:

When inductive components are used for filters in power supplies for electronics, high inductance, the lowest possible DC resistance and a low Q factor are required. The impedance should have a wideband frequency characteristic. In addition to the current rating, the maximum permissible pulse current (switching transient currents) and adequately high core material saturation are important.

RFID Systems:

RFID systems allow contactless identification without direct line-of-sight contact. They are used for wireless data transmission in a range of a few meters. Examples of their application include the automobile industry, logistics, agriculture, medical engineering and security systems. The range of DeMint transponder coils is especially designed for high mechanical stability and high sensitivity as required in the automobile industry for immobilizers, car access systems and tire pressure monitoring systems (TPMS).

DC/DC Converters, Switch-Mode Power Supplies:

Inductive components are used for magnetic energy storage in all kinds of DC/DC converters and switch-mode power supplies. Depending on application, a broad range of different components starting from high-current RF and SMT power inductors up to toroid chokes and transformers can be used.

Signal Processing:

Among other things, signal transformers are notable for being able to transform signals in a large frequency range. They are consequently used in particular in high-speed data transmission (e.g. xDSL) for matching and electrical isolation. Innovative materials and a special winding and coil former design result in low losses, good total harmonic distortion, and fulfilling the requirements on creepage and clearance distances.

EMC Application:

For broadband interference suppression, current-compensated chokes with different core shapes are especially suitable, e.g. ring or D cores and powder core chokes.

Apart from use as filters in mains and other power supply lines, such chokes are important for data lines as used in telecommunications engineering, in line cards, in telephone exchanges (digital and analog), in automotive electronics, and CAN bus applications.

Almost all component families are approved in accordance with the main international standards. All chokes for low-frequency mains networks are dimensioned and tested in compliance with applicable EN and IEC standards.

RF Inductor General Information

DeMint Cuts Inductor Size and Cost:

DeMint utilizes the latest technology enabling the most cost-effective designs in manufacturing inductors. The 0402, 0603, 0805, 1206, 1210, to 1812 series of RF Miniature Inductors all contain wirewound or multi-layer technology with material substrate in ceramic or ferrite cores. Thus providing economic cost with the ultimate performance demanded by today's RF applications. Inductors feature high Q factor, SRFs (self-resonant or series resonant frequency), and Idc (maximum current carrying capacity). RF Inductor product catalogue is avaiable to download at PDF file (1.86MB).

Inductors Selection Notes:

For choke applications, the SRFs (self-resonant or series resonant frequency) is the frequency that provides the best signal blocking.

At the SRF, impedance is at its maximum.
At frequencies below the SRF, impedance increases with frequency.
At frequencies above the SRF, impedance decreases with frequency.

For higher order filter or impedance matching applications, in general, the choice of inductance value typically determines the SRF and vice versa. The higher the inductance value, the lower the SRF, due to increased winding capacitance. It is more important to have a relatively flat inductance curve (constant inductance vs. frequency) near the required frequency. This suggests selecting an inductor with an SRF well above the design frequency. A rule of thumb is to select an inductor with an SRF that is a decade (10X) higher than the operating frequency.

What is Q factor? High Q leads to low insertion loss, minimizing power consumption, and narrow bandwidth. It is important if the inductor is to be used as part of an LC (oscillator) circuit or in narrow bandpass applications. In general, wirewound inductors have much higher Q values than multilayer inductors of the same size and value. DeMint's material science and manufacturing expertise effectively bridges the gap between wire-wound performance and multi-layer inductors with its TRMF100505 (EIA 0402) and TRMI160808 (EIA 0603) series.

How does current requirement affect inductor? Higher current requires larger wire or more threads of the same wire size to keep losses and temperature rise to a minimum. Larger wire lowers the DCR and increases the Q factor. Using a ferrite core inductor with a lower turn count can achieve higher current capacity and lower DCR. Ferrite, however, may introduce new limitations such as larger variation of inductance with temperature, looser tolerances, lower Q, and reduced saturation current ratings. DeMint's ferrite inductors with open magnetic structures, will not saturate, even at full rated current.