Wideband transformers. A new ferrite material for this application, 3E55, is introduced and its advantages are explained. Also 2 new core shapes, EP6 and EP13/LP, developed mainly for use in DSL-applications, are described in detail. A worked-out design example for an ADSL transformer based on the new EP13/LP core set is given.
The MDT software allows application-related parameters to be calculated for all available EPCOS ferrite cores and / or materials. It provides access to their digitized material data including their graphical representations. The user manual of the software contains a detailed description of all functions. The tool can be used as online version, tested in browsers like Google Chrome, Mozilla Firefox, Internet Explorer and Opera, or as download, developed for Windows 7 and 10. The online version does not offer the same comprehensive set of functions as the desktop version.
- Ferrite Transformer Design Ferrite is a magnetic material which is not a metal but a type of ceramic. It consists of either mixed crystals or compounds of ferromagnetic oxides with one or several oxides of bivalent metals like nickle, manganese, zinc etc.
- A ferrite transformer has a magnetic core in which coil (inductor) windings are made on a ferrite core component. It offers low eddy current losses. It is normally used for high-frequency applications. Common ferrite core types are toroidal, closed-core, shell and cylindrical. Depending on circuit designs, core types and applications of transformers, there are different.
- The basic step to building a transformer is to create the model of the object. The model will give you a blueprint of the conceptual results, way before you start investing money and resources in the actual construction of the transformer. While there are many transformer design programs out there, we have out together a list of the top six solutions we believe are the best for transformer design.
The ferrite material list was updated according to the EPCOS Data Book 2017 “Ferrites and Accessories”. The new high frequency material PC200 was added.
Among the features of the current MDT version are:
- Simulations based on user-defined core parameters
- Database expanded to include Steinmetz coefficients for power losses
- Display of complex permeability and impedance as a function of frequency
- Display of impedance Z as the relation between core impedance and frequency
- Transmittable power adjusted for skin and proximity effects (from the wire calculation menu)
- Calculation of the distortion factor (third harmonic) under specific circuit conditions at various temperatures
- Calculation of core loss as a function of signal form
- Specification of wire thickness as per American Wire Gauge (AWG)
To support design-ins you will find the data sheets for all materials by applications under Transformer Core Design
Load current can change the impedance of your ferrite.
The ferrite core in a ferrite bead provides a similar function as the ferrite core in a transformer.
Ferrite bead impedance will change with temperature.
Load current can change the impedance of your ferrite.
What are Ferrite Beads Used For?
Because ferrite bead impedance is inductive, ferrite bead inductors are used to attenuate high-frequency signals in electronic components. When a ferrite bead choke is placed on the power line connecting to an electronic device, it removes any spurious high frequency noise present on a power connection or that is output from a DC power supply. This ferrite clamp use is one of many approach to noise suppression, such as that from a switched-mode power supply. This application of ferrite beads as a ferrite filter provides suppression and elimination of conducted EMI.
Among the various uses of ferrite beads as filters, an EMI filter bead/power supply filter bead is usually rated for a certain DC current threshold. Currents greater than the specified value can damage the component. The troublesome thing is that this limit is drastically affected by heat. As temperature increases, the rated current quickly decreases. Rated current also affects the ferrite's impedance. As DC current increases, a ferrite bead will 'saturate' and lose inductance. At relatively high currents, saturation can reduce the ferrite bead impedance by up to 90%.
Toroid Ferrite Core
Ferrite Bead vs. Inductor
Although a ferrite bead can be modeled as an inductor, ferrite bead inductors do not behave as a typical inductor. If you’re wondering how to measure the behavior of a ferrite bead vs. inductor behavior, you would send an analog signal through the bead and sweep the frequency across several orders of magnitude. If you create a Bode plot for the frequency-swept measurements for a ferrite bead, you’ll find that the ferrite bead provides steeper roll-off at higher frequencies compared to an inductor with similar low frequency behavior.
A simple yet accurate model of a ferrite bead connected to an AC power source.
A ferrite bead can be modeled as capacitors and inductors, and also a resistor in parallel with this RLC network wired with a series resistor. The series resistor quantifies the device’s resistance to DC currents. The inductor in this model represents a ferrite beads primary function of attenuating high-frequency signals, i.e., providing inductive impedance through Faraday’s Law. The parallel resistor in this model accounts for losses in eddy currents that are induced within the ferrite bead at high frequencies. Finally, the capacitor in this model accounts for the component’s natural parasitic capacitance.
When looking at a ferrite bead impedance curve, the primarily resistive impedance is extremely high in only a thin band. The inductance of the bead dominates within this thin band. At higher frequencies, the ferrite bead impedance begins to appear capacitive over and the impedance rapidly decreases. Eventually, as frequency continues increasing, the capacitive impedance will drop to a very small value, and the ferrite bead impedance appears purely resistive.
The ferrite core in a ferrite bead provides a similar function as the ferrite core in a transformer.
Ferrite Bead Selection Guide
Now that you’ve got the ferrite theory under your belt, it’s time to choose one for your device. This is not very difficult, and if you want to know how to select a ferrite bead for a design, you just have to pay attention to a bead’s specifications. You may be wondering, are ferrite beads necessary for my design? Like many engineering decisions, the answer is not so simple. If you know that your board will experience conducted EMI within a specific frequency range, and you need to attenuate these frequencies, then a ferrite bead may be the right choice for your design.
Ferrite Transformer Design
Based on the inductive behavior of ferrite beads, it is natural to conclude that ferrite beads “attenuate high frequencies” without much further consideration. However, ferrite beads do not act like a wideband low-pass filter as they can only help attenuate a specific range of frequencies. You must choose a ferrite bead selection and choke where your undesired frequencies are in its resistive band. If you go a little too low or a little too high the bead will not have the desired effect.
Before selecting a specific ferrite bead for your design, you should see if the manufacturer can provide you with impedance vs. load current curves for the ferrite bead. By far, this is the best tool you can use if you are unsure of how to select a ferrite bead. If your load currents are very high, you’ll need to select a ferrite bead that can withstand them without saturating and losing their impedance within the desired frequency range.
Cautions
Ferrite beads and ferrite chokes are essentially resistive loads at high frequencies, which means they can cause a few problems in your circuit. When placing a bead you’ll need to think about voltage drop and heat dissipation.
In the days of higher voltage circuits, voltage drop wasn’t a big deal. Now we have lots of low power circuits that can use voltages down around 2 V. At those levels, you can’t afford to lose much. Ferrite beads cause a DC voltage drop in your circuit. It may not seem like much, but if your integrated circuits (ICs) have a short high-current draw state, the loss could become significant. Place your ferrite beads where they won’t cause voltage drop issues.
Since ferrite materials are resistive at high frequencies, they primarily dissipate the absorbed energy as heat. This heat isn’t necessarily a problem for your PCB when a ferrite choke is used on a power supply line, but it can become one when it is used to dissipate high frequencies at high current. If your system is especially noisy and the bead will be absorbing lots of high frequencies, this heat could become more of an issue. Make sure to take the bead’s heat dissipation into account.
Ferrite bead impedance will change with temperature.
Ferrite Core On Cable
Ferrite beads can be quite useful, but only if you understand exactly how they work. Remember that they attenuate signals in a fairly small band, and their effectiveness depends on temperature and load current. In order to best use a ferrite bead, you should make sure it meets your exact specifications. Then, when placing the bead, be sure to take voltage drop and heat into account.
We often discuss the importance and function of ferrite beads. If you'd like more info on ferrite beads, check out Everything You Need To Know About Ferrite Beads by industry expert Kella Knack.
Dealing with things like ferrite beads can be difficult, but designing your printed circuit board doesn’t have to be. Altium Designer® is state of the art PCB design software with tools that can help you build the optimal board. It even has add-ons like the power delivery network, which can help you deal with problems like voltage drop and heat dissipation.
Have more questions about ferrite beads? Call an expert at Altium.