Inductors, DC Chokes and Transformers

Hello there guys.

I'd like to ask if someone has an article, application note or pdf notes where are described the different types and the function of inductors, DC chokes and transformers. I thing that the subject Inductor and DC choke would be more important, since those two are subjects to cause big confusion. At least, for Me.

BTW, I have here some photos (of inductors or chokes - don't know) that perhaps someone can tell if it's a inductor or choke.

1st:


2nd:


3rd:


4th


5th


I've dismounted a power supply from a TFT Monitor, from HP, and there was the choke(?) or inductor(?) like in picture number 4 and in another power supply a choke(?) or inductor(?) like in picture number 1.

I have been told that the 1st one and 4th one are chokes. Is that true? What about the other ones. Besides that, what are the differences between a choke and inductor?

There are too another kind of choke(?) or inductor(?) that looks like a resistor. What they are meant for?

Best regards.

Search google using "molded ferrite core inductors"

Dear AMSA84
Hi
Inductor or choke ?? let me simplify a thing ! choke is kind of inductor ! for example you have an RFC , it derived from Radio Frequency Choke . it's impedance will be pretty high instead of your desired frequency , thus it can't allow it to go through ! you understand what i'm trying to say ? if no i can give you more examples .
Best Wishes
Goldsmith

I see, but tell me, in this case, regarding the pictures that I posted, what are those? Specially the 1st and the 4th.

The difference between "inductors" and "chokes" isn't well defined. It's all about how you use them. Depending on the frequency and power level, the first four could all be used as chokes or AC inductors. The fifth is a special case, sine it has two windings and is therefore likely meant to be used as a differential or common mode choke (but even that's not absolute, you could probably use it as an AC transformer as well).

Don't be too caught up in the semantics. Just look at the device characteristics and see if they match your intended application.

AMSA84 said:

I see, but tell me, in this case, regarding the pictures that I posted, what are those? Specially the 1st and the 4th.

Click to expand...

1st one is Hash choke https://elcodis.com/parts/4208846/5220-RC_p2.html

4th one is Ferrite drum choke
**broken link removed**

- - - Updated - - -

Others are Toroid Chokes if there is one coil or Toroidal Transformer if more than one coil and there is no interconnection between the coils.

I see. But in this case, what you mean for the 1st one is that, looking at the specification, we consider this inductor as a choke inductor that is able to suppress all the high frequency interference starting from 7.96MHz?

About the 4th one, drum choke, is for the same purpose?

What are the difference between them? When one is used and when the other is used?

papunblg said:

1st one is Hash choke https://elcodis.com/parts/4208846/5220-RC_p2.html

4th one is Ferrite drum choke
**broken link removed**

- - - Updated - - -

Others are Toroid Chokes if there is one coil or Toroidal Transformer if more than one coil and there is no interconnection between the coils.

Click to expand...

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So what you mean is that we can use one or the other to do the job. I mean, for example, if I take one inductor from a SMPS from a TFT Monitor, CRT Monitor or whatever, that looks like the 4th one, I can use it as the inductor in the LC filter to suppress my needs, in my design, for example in a buck converter that has a Io=1A (if has the value of L bigger than that I've computed) or I can use it as a choke, computing the frequency that will suppress then high frequency interference based on the L measured with the LCR meter. Is that it?

mtwieg said:

The difference between "inductors" and "chokes" isn't well defined. It's all about how you use them. Depending on the frequency and power level, the first four could all be used as chokes or AC inductors. The fifth is a special case, sine it has two windings and is therefore likely meant to be used as a differential or common mode choke (but even that's not absolute, you could probably use it as an AC transformer as well).

Don't be too caught up in the semantics. Just look at the device characteristics and see if they match your intended application.

Click to expand...

Thank you guys for the answer.

Best regards

EDIT:

I am asking this because I want to build a buck converter and of course I'll need the inductor for the LC filter. Instead of building one (this will be the next task) I could use one of those inductor that I posted because I've lot's of them, removed from different kinds of SMPS, TFT Monitor, CRT Monitors, etc.

AMSA84 said:

So what you mean is that we can use one or the other to do the job. I mean, for example, if I take one inductor from a SMPS from a TFT Monitor, CRT Monitor or whatever, that looks like the 4th one, I can use it as the inductor in the LC filter to suppress my needs

Click to expand...

My G-O-D ! Where did I mention that in my post?
The material that used to concentrate the flux produced by current in acoil is referred to as core. In choke coils used for limiting currents it increses the flux density to provide large inductance. In transformers it is used to link the flux produced by primary winding to the secondary windings for efficient transfer of power from primary to secondary. A wide variety of core materials are used in practice. For use at lower radio frequencies, ferrite cores are used. They provide higher efficiency. At high radio frequency , generally no core is used (air core). etc. It all depends upon application type.

RF inductor selection involves these key parameters:mounting (surface mount or through-hole), inductance value, current rating, DC resistance (DCR), self-resonant frequency (SRF), Q factor, and temperature rating. While small size is typically desired, the laws of physics limit how small an inductor can be
for a given application. Inductance value and current rating are the chief determinants of size; other parameters can then be optimized.

papunblg, I'm sorry if you misunderstood but that part of the post was to mtwieg, since he has refered that "The difference between "inductors" and "chokes" isn't well defined. It's all about how you use them. Depending on the frequency and power level, the first four could all be used as chokes or AC inductors."

But thanks for your reply.

AMSA84 said:

So what you mean is that we can use one or the other to do the job. I mean, for example, if I take one inductor from a SMPS from a TFT Monitor, CRT Monitor or whatever, that looks like the 4th one, I can use it as the inductor in the LC filter to suppress my needs, in my design, for example in a buck converter that has a Io=1A (if has the value of L bigger than that I've computed) or I can use it as a choke, computing the frequency that will suppress then high frequency interference based on the L measured with the LCR meter. Is that it?

Click to expand...

No, I didn't say that either. What I'm saying is that words like "choke" or "inductor" are so vague that they're practically useless. Making a decision requires much more information on the parts (ESR, saturation current, core material, etc), as well as information on the intended use of the component.

Totally agree. In fact just think of them as "wound components" when you see them, and then figure out their intended purpose by seeing where in the circuit it is being used.

I mean, for example, if I take one inductor from a SMPS from a TFT Monitor, CRT Monitor or whatever, that looks like the 4th one, I can use it as the inductor in the LC filter to suppress my needs, in my design

Click to expand...

Sometimes it's hard to re-use wound components without some measurements or experimentation; although you may wish to reuse bits of your TFT monitor, the fact is that the black/grey material comes in different characteristics, and they all look alike. A visual inspection won't tell you much, although the size of the core and wire, and the location in the monitor where you extracted it from will let you know the intended purpose, and these are approximate clues. Another good way is to check out what IC they are connected to, and look up the datasheet. if you want a predictable performance in your design, then you'll likely need to buy a known component (or known core and wind your own). Or be prepared to experiment. And keep a temp probe to see how hot your wound component is getting in your design. Maybe I'm a bit paranoid but I will only buy cores from reputable dealers (Farnell, mouser etc), so I'm certain that the core material is what I intended to have, and not mistakenly given the wrong material.

1st, it is rod chock, material of rod is Ni-Zn, which can pass some DC currents, inductance is lower, e.g. in RC or LC circuit, we can use the rod chock as inductor.
2st, it is toroidal choke, material of toroidal core is powder iron, which can pass some DC currents, inductance is not very high, it is used as filter in circuit.
3st, can not see the core, I guess core is Powder iron or Fe-Si-Al or high flux or MPP material, sometime we use it as PFC inductor or storage energy inductor.
4st, it is DR chock, material of core is Ni-Zn, inductor is not very higher, we should be consider Isat and Irms when we use it, it is DC choke.
5st, it is commn mode choke, material of core is Mn-Zn, it is high permeability material, which can not pass DC current, only pass AC current, inductor is very higher, as CMC in circuit.

Thank you very much for your reply.

Hello again guys.

I have a high-frequency transformer that I took away from a TV PSU and I want to separate the core from the wires support. So, my question is if anyone know how to separate the two cores that looks like that are pasted to each other? I want to do that in order to reuse the core and the case.

Regards.

They are usually epoxy glued. You can soften the joint and disassemble the core by applying hot air or placing the part in a baking oven. The core material doesn't suffer from high temperature, but not sure if you'll manage to keep the coil former intact.