Why Ferrite Bead in Supply line

In summary: For example, if your application draws 10mA, go for a bead with a current rating of 20mA.Finally, the "resistance" of the ferrite bead is determined by the size and shape of the ferrite core, the surrounding insulation, and the overall design of the RF connector. Generally speaking, the higher the frequency, the higher the resistance of the ferrite. Ferrite beads are available in a number of shapes, such as cylinders, disks, and bars. The shape of the ferrite bead is not as important as the size and shape of the ferrite core. The larger and more shape-memory the ferrite core, the higher the resistance. However, the shape of the ferrite
  • #1
Dinu Paulson
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0
Presently Am try to design a USB to UART,485& 232 board, in that Am using FTDI USB to UART converter, In the FTDI data sheet they providing some sample design and A ferrite bead is connected in series with the USB power supply to reduce EMI noise from the FT232R and
associated circuitry being radiated down the USB cable to the USB host. The value of the Ferrite Bead depends on the total current drawn by the application. A suitable range of Ferrite Beads is available from Steward (www.steward.com[/URL]), for example Steward Part # MI0805K400R-10,, So guys could you please tell me How we choose the right part number, my apllication will draw maximum of 30mAs
 
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  • #2
Dinu Paulson said:
Presently Am try to design a USB to UART,485& 232 board, in that Am using FTDI USB to UART converter, In the FTDI data sheet they providing some sample design and A ferrite bead is connected in series with the USB power supply to reduce EMI noise from the FT232R and
associated circuitry being radiated down the USB cable to the USB host. The value of the Ferrite Bead depends on the total current drawn by the application. A suitable range of Ferrite Beads is available from Steward (www.steward.com[/URL]), for example Steward Part # MI0805K400R-10,, So guys could you please tell me How we choose the right part number, my apllication will draw maximum of 30mAs[/QUOTE]

The part number you list does seem appropriate for the application. This page will help you understand the various parts of that part number:

[PLAIN]http://lairdtech.thomasnet.com/Asset/Part-Number-Nomenclature-FErrite-EMI.pdf

(Steward appears to have been absorbed by Lairdtech)

In general when you choose ferrite beads for RF impedance insertion, you will first choose the bead material (the ferrite) to match the frequency range where you want a good impedance. With some vendors, materials like #43 are a good match for mid-frequency RF (100-300MHz). Whatever material is being used in this bead is reasonable in its impedance versus frequency plots, although it does appear weighted to higher frequencies (500-900MHz), which may be less of a problem for you in your application.

After the choice of ferrite material, you then choose a bead based on how much "resistance" you want in your frequency range, and choose one that is physically big enough not to saturate with your DC current. Pick a bead that has a rated current value that is at least 2x your application current.
 
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1. Why is a ferrite bead used in a supply line?

A ferrite bead is used in a supply line to suppress high-frequency noise and interference. It acts as a passive filter, absorbing and dissipating the noise before it reaches the electronic device.

2. What is the purpose of a ferrite bead?

The purpose of a ferrite bead is to reduce electromagnetic interference (EMI) and radio frequency interference (RFI) in electronic circuits. It also helps to improve the overall performance and reliability of the circuit.

3. How does a ferrite bead work?

A ferrite bead works by using its high-frequency impedance to resist and absorb noise signals. It is made of a ceramic material called ferrite, which has high magnetic permeability and can effectively suppress high-frequency noise.

4. Where should a ferrite bead be placed in a circuit?

A ferrite bead should be placed as close to the source of noise as possible. This could be near the power supply, on the input/output lines, or at the connection point between the circuit and the external device. Placing it too far away from the noise source may reduce its effectiveness.

5. Are there different types of ferrite beads for different applications?

Yes, there are different types of ferrite beads for different applications. They vary in their size, shape, and impedance characteristics to suit different frequencies and noise levels. It is important to choose the right ferrite bead for the specific circuit and noise source to achieve optimal performance.

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