Author Topic: Chokes and Inductors ...  (Read 11658 times)

0 Members and 1 Guest are viewing this topic.

Offline Slothie

  • Regular Contributor
  • *
  • Posts: 63
Chokes and Inductors ...
« on: July 21, 2012, 08:44:23 am »
... are they the same thing? If you look at the component catalogues they seem to make a distinction, but what actually is the difference? I have a couple of axial chokes or 5.6uH and I need a ~5uH inductor for a switch mode voltage converter. Is it going to do? Or is there something special about the cores in "chokes" rather than inductors?

Ian
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15307
  • Country: za
Re: Chokes and Inductors ...
« Reply #1 on: July 21, 2012, 08:51:04 am »
Same thing, like capacitors are often referred to as condensers.
 

Offline Simon

  • Global Moderator
  • *****
  • Posts: 14208
  • Country: gb
  • Did that just blow up? No? might work after all !!
    • Simon's Electronics
Re: Chokes and Inductors ...
« Reply #2 on: July 21, 2012, 09:03:10 am »
Inductors and chokes alike will have characteristics other than their inductance but the two words are synonymous and often used based on context
https://www.simonselectronics.co.uk/shop
Varied stock of test instruments and components including EEVblog gear and Wurth Elektronik Books.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 

Offline PeterG

  • Frequent Contributor
  • **
  • Posts: 813
  • Country: au
Re: Chokes and Inductors ...
« Reply #3 on: July 21, 2012, 09:10:44 am »
They are both the same thing, however I have only seen inductors called Chokes when used in high power devices such as UPS units.

Regards
Testing one two three...
 

Offline A Hellene

  • Frequent Contributor
  • **
  • Posts: 601
  • Country: gr
Re: Chokes and Inductors ...
« Reply #4 on: July 21, 2012, 09:24:54 am »
Chokes, transformers, fly-backs, toroidals, ferrite beads, coils, etc., ARE inductors, which, as a term, denotes the family including any passive electrical component with inductive behavior and properties.

'Inductor' is a general term, like capacitor, resistor, semiconductor, etc.


-George
Hi! This is George; and I am three and a half years old!
(This was one of my latest realisations, now in my early fifties!...)
 

Online TerminalJack505

  • Super Contributor
  • ***
  • Posts: 1276
  • Country: 00
Re: Chokes and Inductors ...
« Reply #5 on: July 21, 2012, 09:29:20 am »
I've always wondered about this too.  I think the term 'choke' is used for a specific mode of operation for an inductor.  That is, the term 'choke' is used when an inductor is being used for filtering purposes.

If this is the case then I think there can be a difference between a choke and an inductor in that a 'choke' may (purposely) have a lower Q factor than a traditional 'inductor'. 

You would be better off using a choke (aka low Q factor inductor) for EMI filtering, for example.  The lower Q factor will cause the absorbed high-frequency energy to be dissipated as heat rather than returning the energy back to the circuit.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2033
  • Country: us
Re: Chokes and Inductors ...
« Reply #6 on: July 21, 2012, 09:44:05 am »
Chokes are inductors designed for high DC current (much higher than their RF current).  They also have high losses since they are used as filters they need to block and/or dissipate RF, not store energy efficiently.

Normal inductors are designed for DC current either smaller or of the same order as the AC current.

 

Offline T4P

  • Super Contributor
  • ***
  • Posts: 3706
  • Country: sg
    • T4P
Re: Chokes and Inductors ...
« Reply #7 on: July 21, 2012, 07:42:53 pm »
A Choke is not intended to be part of a LC circuit, but being of a LARGE size compared to inductors of the same rating as they dissipate heat in the AC input
A choke is basically a AC Choke, it literally chokes the AC and dissipates off the excess AC
They really aren't meant to be a store and release sort of thing, it's more of a lossy inductor
 

Offline madires

  • Super Contributor
  • ***
  • Posts: 4903
  • Country: de
  • A qualified hobbyist ;)
Re: Chokes and Inductors ...
« Reply #8 on: July 21, 2012, 08:11:44 pm »
I've always wondered about this too.  I think the term 'choke' is used for a specific mode of operation for an inductor.  That is, the term 'choke' is used when an inductor is being used for filtering purposes.

Yep, if an inductor is used to block high frequencies it's called a choke, e.g. a common mode choke.
 

Offline A Hellene

  • Frequent Contributor
  • **
  • Posts: 601
  • Country: gr
Re: Chokes and Inductors ...
« Reply #9 on: July 21, 2012, 10:14:07 pm »
Alright! Chokes are not only the inductors that 'choke' (kill, block or eliminate) the AC component in DC lines or the HF component in LF lines. The older members might remember with a smile the VK200 RFC (RFC: Radio Frequency Choke) that was widely used in the RF equipment of the seventies/eighties.

It took me a while to find a picture of the infamous VK200 RF choke:


But chokes are not only used for filtering. For example, the DC-DC flyback converters are called 'ringing choke converters' because the flyback inductor is not really a transformer; it is a choke actually (we should better call it a coil), often with a primary and a secondary winding, or with extra auxiliary secondaries. Why the flyback coil cannot be called a transformer? Simply, because in transformers the energy transfer happens directly from the primary to the secondary windings and at the same time. In the flyback, instead, the primary does not transfer energy to the secondary but it charges the magnetic material of the inductor, while the magnetics are discharged by the use of the secondary winding of the flyback inductor.

Now, if we can use the same exactly inductor we have just discussed at the flyback example above, and we use it in forward topology, only then we could call this specific inductor a transformer; but we cannot do that because a transformer needs a magnetic medium of different properties than those of a flyback coil.

This is an excerpt of a piece I wrote about flyback converters:
"Actually, [at the Flyback Topology] we are not talking about a transformer because we do not collect the energy as we are pushing it to the primary winding; this is the Forward Topology. Instead, we collect the energy stored in the magnetic medium, which is the ferritic core. So, this is two coils coupled magnetically together using the same ferritic core, where the primary creates energy that is stored in the visible air-gap of the ferrite core (or in the invisible countless tiny gaps created by the bonding material of the ferritic powder the ferrite cores are made of), and we discharge the coil's energy by using the second coil (the "secondary"). This is the so-called Flyback Topology that energised the electron beam of the TVs, where it was firstly used commercially and, thus, became widely known; the electron beam that "flew back" to the next line of the field/frame during the blanking time after rendering the end of the previous line."


-George
Hi! This is George; and I am three and a half years old!
(This was one of my latest realisations, now in my early fifties!...)
 

Offline madires

  • Super Contributor
  • ***
  • Posts: 4903
  • Country: de
  • A qualified hobbyist ;)
Re: Chokes and Inductors ...
« Reply #10 on: July 22, 2012, 02:21:46 pm »
But chokes are not only used for filtering. For example, the DC-DC flyback converters are called 'ringing choke converters' because the flyback inductor is not really a transformer; it is a choke actually (we should better call it a coil), often with a primary and a secondary winding, or with extra auxiliary secondaries. Why the flyback coil cannot be called a transformer? Simply, because in transformers the energy transfer happens directly from the primary to the secondary windings and at the same time. In the flyback, instead, the primary does not transfer energy to the secondary but it charges the magnetic material of the inductor, while the magnetics are discharged by the use of the secondary winding of the flyback inductor.

I think it's called a storage throttle. But with a primary and a secondary winding it's a transformer ;-) The difference is how we drive that transformer, i.e with a nice AC causing a magnetic flux or with DC impulses while storing their energy in a magnetic field. If I would take the flyback coil from above (primary and secondary windings) and drive it with AC there will be a magnetic flux inducing voltage into the secondary winding, matching your description of the classic AC transformer.
 

Offline A Hellene

  • Frequent Contributor
  • **
  • Posts: 601
  • Country: gr
Re: Chokes and Inductors ...
« Reply #11 on: July 22, 2012, 05:52:46 pm »
A coil having both a primary and a secondary windings is not necessarily a transformer; it could either be a transformer or a flyback or just two coils magnetically coupled together (i.e. the SEPIC dual inductor). What makes the distinction is not how the primary is driven, but how the energy is collected from the secondary.

Inductors and their windings have a polarity. Assuming that the primary has a positive drive, we can collect the energy from the secondary either by using both the positive and the negative phase outputs, or, by the use of rectifiers, the positive phase output only or the negative phase output only.

In the first two cases we have a forward topology and the inductor can safely be called a transformer because the energy transfer is direct and immediate from the primary to the magnetically coupled secondary.

In the third case we have a flyback topology, and the inductor can not be called a transformer any more because there is not any direct energy transfer from the primary to the secondary windings; instead there is energy storage from the primary to the magnetic medium and energy harvesting from the magnetics by both the primary and the secondary windings after a delay determined by the driver and the inductor circuit resonance, where the stored energy will pick the easiest path to flow no matter if this path is through the primary or the secondary or through both the windings. The most simple examples of this topology are the boost/buck/buck-boost converters, where the inductors they use do not have a secondary winding.

Of course, conventionally, we call every inductor with more than one windings, a transformer.


-George
Hi! This is George; and I am three and a half years old!
(This was one of my latest realisations, now in my early fifties!...)
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15307
  • Country: za
Re: Chokes and Inductors ...
« Reply #12 on: July 22, 2012, 06:14:36 pm »
I have seen a few designs of TV sets that use the forward and flyback sides. A single winding that delivers +200V and -20V from the same winding. You look carefully at the component list and see the diodes are both 1000V silicon fast recovery diodes, and a supply that supplies 200V at 100mA and -20V 1A, but uses 3A diodes for both units, and they run hot for both diodes.
 

Offline G7PSK

  • Super Contributor
  • ***
  • Posts: 3661
  • Country: gb
  • It is hot until proved not.
Re: Chokes and Inductors ...
« Reply #13 on: July 22, 2012, 06:22:19 pm »
Choke's is the early or original term for an inductance much in the same way as condenser was the early or original term for a capacitor. The choke was seen back then as throttling or choking the flow of electricity in much the same fashion as a condenser (or Condensor as it was spell't then) was seen as literally condensing electricity.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf