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Ferrites as a Filtering Element - Are They Effective?

Altium Academy

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*Ferrites as a Filtering Element - Are They Effective?*

Welcome back to Altium Academy! In this video, host Zach Peterson dives into the effectiveness of ferrite beads as filtering elements in PCB design. He compares ferrite bead filters with pi filters and RC filters using SPICE simulations in Altium Designer to determine their efficacy.

🎥 *What You’ll Learn:*
The role of ferrite beads in high-frequency noise reduction
Comparative analysis of ferrite bead, pi, and RC filters
Practical insights from SPICE simulation results

📌 *Key Takeaways:*
Ferrite bead effectiveness in DC power filtering
Pros and cons of different filter types
Real-world applications and limitations of ferrite beads

If you’re designing PCBs and curious about noise filtering solutions, this video is for you! Follow along in Altium Designer and see the simulations in action. Need Altium Designer? Get a free trial here: Make sure to like, subscribe, and leave your comments or questions below. Don’t forget to call your fabricator, folks!

#FerriteBeadFilter #PCBDesign #AltiumDesigner #NoiseReduction #FilterComparison

👉 Three Frequency Ranges For Ferrite Bead Usage: https://resources.altium.com/p/three-...

👉 Ferrites in PCB Design: What the Experts Say: Ferrites in Digital PDN: What the PCB Expe...

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0:00 Intro
0:42 Ferrites as a Filtering Element
1:55 Comparing the Ferrite Bead Filter

19 Comments

@TheDutchGuyOnYT 2 years ago

Can somebody put a ferrite between Altium and the stupid idea to cancel perpetual maintenance? I’m very angry.

@marcdraco 1 year ago

I recently converted a "reference" design from a large company - where they're split the grounds and used FBs all over the place. So I took a leap of faith (based on advice from Rick Hartley and Eric Bogatin. And it works a charm. Lower BOM cost, fewer parts and my nerves aren't shattered.

@rfrisbee1 2 years ago

The main difference between a ferrite bead and an inductor when used as a filter is that the ferrite bead, if chosen correctly, will convert the noise energy into heat, whereas an inductor will just cause it to slosh around until some other lossy element(s) in the circuit convert it to heat.

The complicated part in the above is the "if chosen correctly". The noise energy must fall within the lossy frequency range of the bead and the bead must be modelled at the DC current it is going to run at, as the parameters change with current!

As for datasheets, well we can't even get manufacturers to stop recommending parallel 10nF + 1uF (or similar) surface mount capacitors for IC decoupling, when using a single 1uF ceramic surface mount capacitor would be better (cost, size, performance) in the vast majority of cases. Good luck getting them to stop recommending the use of ferrite beads on power rails to ICs!

@myetis1990 2 years ago

Thank you Zach, for the great video. While I was trying to take a look at ferrite beads, I learned something nice about the PI filter, thank you.

@FriedemannSchmidt-te9kq 2 years ago

Can you please carry out a simulation with higher capacitor values, with at least 10µF?

@Rubacava_ 2 years ago

You also have to account for series resistance and the load current. Ferrite is basically an inductor + resistor. It doens't have that resonance but you can only power so much with it. It is usually cheaper and smaller too so it still has its uses.

@eewheezard 9 months ago

Yes it really works that way

@Fisch4678 2 years ago

Thank you for the nice video :)
I agree that the damping of an LC filter is generally better than that of a ferrite bead filter.
But a real-world inductor will also have some parasitic capacitance, which will dominate at frequencies above the self-resonance-frequency (SRF). So the AC transfer characteristic of a real-world LC filter will also be messed up at high frequencies... just like the ferrite bead.
Furthermore, a real-world capacitor will also have some parasitic inductance, which will further degrade the filter's performance at high frequencies in each of the three designs.

I sometimes add a ferrite bead pi-filter on the output of a DC/DC converter to provide some damping for high-frequency noise (frequencies at which the regular LC filter of the converter doesn't work due to the parasitics).

All the ferrite beads I've come across have a specified bandwidth of 100MHz, not 10MHz. My intuition always was, that an inductor with a similar SRF must necessarily have a very low inductance, which results in an increased cut-off frequency of the filter compared to the ferrite bead.
Thus, if I can trade off the worse damping for a lower cut-off frequency, the ferrite will do better.
Your video really made me think about my past design choices and I will definitely do some more simulations in the future :)

@schmitzbeats6102 2 years ago

I think the parameters of the "model" of that bead is flawed. Isn't the parallel resistor a tad small and your parallel capacitance a tad high?! Looking at the LTSpice Model parameters for parts that have an inductance in the 150nH range (Würth 742792097) gives me 35 ohms and 800f as in FEMPTO farads. Nowhere near 1.5n... Also you are unlikely encounter a scenario where there is no additional capacitance like 100n decoupling near the load or somewhere towards the power source.

@haldanecollins3735 2 years ago

I guess this is a body blow to for example the Mil-DTL 38999 and ARINC 600 filtered connector markets.

@radsdau 2 years ago

Zach, you mention the video links in the description, for info about how ferrites add noise when you're trying to remove noise... did I miss that link? Seems like something I need to learn more about. Thanks.

@bertalankercso831 1 year ago (edited)

Parallel capacitance of a 120R@100MHz 0805 ferrite is around 30pF (not 1.5nF...). And, on high frequency modelling, one should add a series resistor representing ESR of the ferrite - do not simulate without it! (This is 120ohm @100MHz, 60ohm @50MHz and so on, see datasheet.)

@ChrisMayfield51291 2 years ago

your analysis ignores the fact that the damped LC circuit has a considerable loss at lower frequencies and lower loads due to the series resistance. you're attempting to power the load with 5V, but only 1.67V is making it to the load (in the 5ohm case) due to most of the voltage being dropped across the 10 ohm resistor. I would say the ferrite bead is still a better alternative in the examples provided as the 5V DC actually makes it fully to the load and removing the series resistance on the LC circuit re-introduces the resonant peaking.

@samratroy1487 2 years ago

I was using a ferrite bead pi circuit filter for a converter but was getting some issues with conductive emissions, so increased the capacitance and replaced the ferrite bead with inductor but still getting noise around 500kHz. Anyone any suggestions?

@dukeibzusa 2 years ago

What about if it is recommended by the IC manufacturer

@sjwpcbdesign 2 years ago

So, the big question is this, why continue to manufacturer ferrite beads if they provide no benefit according to simulations. What actual use case does a ferrite bead serve?

@АлексейБулдаков-п7з 2 years ago (edited)

It seems to me that the bead replacement scheme is not correct. On your circuit, the impedance is no more than 10 ohms. If you look at the data on the impedance graphs of the data sheets of beads, there will be large values. What about this?

@87Spectr 2 years ago

Thanks for video!
1. Inductor has parasitic capacity, capacitor has parasitic inductance. You draw only equivalent scheme of FB... Is this not important?
2. LC-filter will be effective in high frequency when his cut off freq = 100kHz, and DC 2..3A ? it means that inductor and caps are big sizes, big parasitic.

@ats89117 2 years ago

Ignorance is bliss. Ferrites are useful for adding high frequency RESISTANCE and they are appropriately used in the frequency range above where their inductive reactance has fallen well below their resistance. Perhaps Zach should listen to read some of the material that was put out by Jim Williams, Henry Ott and many others decades ago...