16
votes
Accepted
Why do toroid inductors have a square cross-section?
When making a ferrite toroid, you start with powder that has to be compressed, then sintered. It's much more practical to have a mould with substantially parallel sides, and compress in one direction. ...
- 166k
16
votes
Ferrite bead selection
If you are using the ferrite bead primarily to filter unwanted RF, both inductance and resistance are helpful. Filters can be made either way, with inductors or resistors. Higher impedance provides ...
- 29.3k
12
votes
Accepted
Question on EMI filtering
I've designed a number of switching supplies that had to pass various EMC standards starting at 30MHz and up, and I can say that ferrite beads are excellent at frequencies of 100MHz and above, but not ...
- 309
12
votes
Accepted
Is this a good idea to separate Grounds via ferrite beads?
Usually anything that increases impedance between grounds will have undesirable side effects. Also, sometimes ferrite beads lead to oscillation or ringing at low to moderate frequencies. I would ...
- 29.3k
10
votes
ATtiny85 and high frequency PWM for driving a ferrite transformer
In an ATtinyXX there are two timers. Timer0 can be clocked at the same CPU frequency, by setting the corresponding bits (see below) in the TCCR0B (for timer 0).
At ...
- 5,357
10
votes
Question on EMI filtering
Ferrite beads are not even that lossy at such relatively low frequencies, they behave more like a (small, a few uH) inductor, which can be a trap for the unwary.
They're more useful at VHF and higher ...
- 398k
10
votes
Accepted
USB 2.0 VBUS Filter
Letters and Decimal Points
What does 5V0 mean? I've seen this net name used in other USB circuit diagrams (figure 1 here for example). Is 5V0 a convention used to indicate something different from ...
- 7,000
9
votes
Accepted
Difference between RF ferrite and normal ferrite
Ferrites come in a variety of flavors. The main groups are ferrites for
Filters (for signal filtering, e.g. in telecommunications)
Power Conversion
Interference suppression (EMI filters, not to be ...
- 18.4k
9
votes
Why do toroid inductors have a square cross-section?
Space occupancy consideration
For the same volume of core material, the “important” outer dimensions of the finished product will be smaller if a square cross section is used. Hence, for example, it ...
- 457k
9
votes
Question on EMI filtering
He's right. Most ferrite beads are rated at 100 MHz and up. They have minimal impact in the 1 - 100 MHz range, which is what he's interested in.
And since as a ham, he's operating sensitive receivers ...
- 173k
8
votes
Chokes vs. small capacitors on signal cables
A common mode ferrite sleeve that is lossy at radio frequencies and doesn't attenuate the signal is rather more useful on a data cable than shunt capacitors that attenuate the signal and reflect ...
- 166k
8
votes
How to compare a magnetic loop antenna to a conventional antenna
It's pretty common to use a ferrite core for signals around 1 MHz. Consider the standard ferrite rod coil in a regular AM receiver: -
Picture from here.
It uses a ferrite rod because it improves the ...
- 457k
7
votes
Accepted
Why do some computer power cables not have ferrite beads? What type is usually used?
A ferrite bead around a cable adds common mode inductance to the cable. The purpose is to increase the impedance of the cable at high frequencies. With higher impedance, less power can be radiated ...
- 313k
7
votes
Core loss kW/cm³: UNFAMILIAR FACTOR
If you're used to iron cores at mains frequencies, where saturation is the practical limit, or air-cores at RF frequencies, where neither saturation nor core heating occur, then ferrite cores will ...
- 166k
7
votes
EMC 30-50 MHz emssions
If my PCB is not too large (15cm x 5cm) 30-50 MHz emissions are mainly
radiated through power cables?
Yes, that is a general truth and, that means you need to prevent conducted emissions because on a ...
- 457k
7
votes
Ferrite bead selection
There isn’t a simple answer. Beads not only are sized differently, but are made from a variety of materials that have different characteristics. Some work best for blocking low frequency but don’t ...
- 54.1k
7
votes
Value of a ferrite bead in PHYs
Almost all ferrite beads are specified with their impedance at 100 MHz. This does not imply that they behave the same at other frequencies:
(source: Murata SMD/BLOCK Type EMI Suppression Filters ...
- 19.3k
6
votes
Is this symbol another version of a ferrite bead symbol?
Yes, it is indeed a ferrite bead symbol.
There are standards for component symbols, however as with all standards, people choose not to follow them, and instead make up their own variants (obligatory ...
- 66.1k
5
votes
Accepted
Simple AM radio - how to modify it so it can work without ferrite rod antenna?
Your coil in parallel with the variable capacitor works as a bandpass filter. Filtering just the station you want to hear.
The frequency selected depends upon the capacitor and the coil. The formula ...
- 407
5
votes
Chokes vs. small capacitors on signal cables
Most EMC problems that products have are to do with Radiated EMC. When you have normal tests done like say FCC A and B getting a radiated fail is not uncommon. Radiated EMC is generally due to common ...
- 14.7k
5
votes
How to compare a magnetic loop antenna to a conventional antenna
No, the ferrite does not introduce noise. But it can lead to nonlinearity. If you want to build compact, then a ferrite is the way to go.
- 7,430
5
votes
EMC 30-50 MHz emssions
If my PCB is not too large (15cm x 5cm) 30-50 MHz emissions are mainly radiated through power cables?
Maybe. Maybe not! Point is, a shorter conductor can still emit – maybe not as efficiently, but ...
- 94.9k
5
votes
EMC 30-50 MHz emssions
Let us consider resonant parasitics.
1uH and 1pF will resonate at 150MHz.
10nanoHenry and 100pF will resonate at 150MHz.
1u and 100pF will resonate at sqrt(100) lower, or 15MHz.
100nanoHenry and 100pF ...
- 34.3k
5
votes
Short circuited ferrite bead on PCB
Ferrite beads are meant to have very low resistance at DC, typically less than 5 ohms, and often less than 1 ohm.
If they fail, they tend to fail open-circuit (high resistance) rather than short-...
- 130k
5
votes
Accepted
Which frequency should be considered for inductor design in this FOT (fixed on time) PFC?
A borderline conduction mode (BCM) PFC exhibits wide frequency variations across the sinusoidal input. The minimum operating frequency is reached at the top of the sine wave. Usually, one design ...
- 22.2k
5
votes
Accepted
What are the differences between these ferrite cores?
EC and ETD are almost identical. ER is slightly different.
EC and ETD (ETD means economic transformer design) have both circular centre leg and circular winding window. ER's winding window is not ...
- 34.4k
5
votes
What is this black thing on my mouse's cable? Is it related to the mouse not working?
The ferrite core on a mouse cable is simply a tube-shaped piece of magnetic material that the cable passes through. It is there to reduce radio frequency signals on the cable. It will have nothing to ...
- 23.4k
4
votes
Accepted
How to properly wind a high frequency / high voltage transformer?
No matter how you look at it you are pumping DC into the transformer primary. The FET's source is going to be wanting to produce a square wave from 0V to +12V and the transformer will want a primary ...
- 457k
4
votes
Accepted
What is this circular rod with wired wrapped 'coil' and ceramic capacitor?
I'm using 3 pieces of information to suggest a hypothesis as to the function of that device:
It's an LC tank circuit, and so will have an RF resonant frequency (which could be calculated from the ...
- 17.9k
Only top scored, non community-wiki answers of a minimum length are eligible