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All You Need To Know About Ferrites in Broadband Transformers

Ferrites in Broadband Transformers

Broadband Transformers are magnetic systems used to transfer energy over different frequencies. They are wound on ferrite cores, such as toroidal cores & POT cores for their higher permeability, higher efficiency, excellent RFI performance, good frequency response, & no leakage magnetic flux. One of the common applications of these transformers is telecommunication equipment, where they are used widely at low power levels.

In this blog, we’re going to take a closer look at broadband transformers, their purpose & how they use ferrites to boost their operations. Let’s get started!

Types of Broadband Transformers

1. Conventional Transformers: These transformers transfer electrical energy from one circuit to another at a similar frequency but at different voltage. Their work is based on the principle of electromagnetic induction. They’ve two windings- primary & secondary, similar to power & audio transformers.

2. Transmission Line Transformers: These transformers are usually wounded on ferrites or powdered iron cores while using parallel windings. They are more efficient than the conventional ones. For example, balun transformers.

Purpose of Broadband Transformers

Broadband transformers are meant to work in different frequencies where both XL or XC have their unique one or more frequency ranges. For this, you need to use ferrite cores with high-permeability that have small windings as desired for the MF & HF spectrums. When the operating frequency increases, the core becomes obvious to the circuit.

During this time, the winding of the ferrite is solely working at the upper range of operation. If you see the lower end of the frequency range, the core is visible through the circuit. It allows the winding to produce the required inductance in the low frequency of the operating range.

An important parameter in transformers is shunt reactance, which increases with frequency. But this only happens if the permeability of the material is constant or decreasing at a rate lesser than the increase in frequency.

This happens even in transformers that have ferrites with f1 at the higher end of the permeability v/s frequency curve. Here, the whole bandpass is located in the area where the initial permeability is reduced, still its characteristics are not affected.

How are Ferrites used in Broadband Transformers?

Ferrites are the most appropriate & cost-effective material used in broadband transformers. They provide the highest impedance in the frequency of unwanted noise signals & always have a high initial permeability at lower cut-off frequency.

Usually, ferrites are selected depending on their characteristics, such as the ease of winding, terminating & some technical design constraints of the transformer.

For example, Manganese Zinc (MnZn) ferrites are suitable for the low & medium frequency transformer designs. When these ferrites are in the broadband transformers, the core geometry should be the ratio of DC resistance to the inductance for a single turn, which is minimum.

For transformers that have an overlaying direct current, gapped ferrite cores can control the reduction in shunt inductance.

On the other hand, high-frequency transformers are well-suited with toroidal core-shaped ferrites. A few turns that are needed can be wounded on the toroid. But keep a note that windings with lesser turns lead to issues in obtaining the desired impedance ratios. To minimise the leakage inductance, the primary & secondary windings are coupled.