hi there, can you please tell me how do the choke filter circuits work?

is it the inductor is the source of noise? if it is true, what is the reason?

thank you..

 

A choke filter is an inductor.

A choke filter is just that, a filter. In most cases an ideal choke filter would filter out all AC noise and only let through a DC signal, so you will see them in a lot of powersupply circuits. All components are not ideal though, so it will let through very low frequency AC signals, but filter out the high frequency AC signals, still letting through DC.

You need to learn about inductive reactance then you will more fully understand what I'm talking about.

Inductors are not the source of noise.

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Purely reactive components do not generate noise. SO, it is not a source of noise. The small series resistance of the conductor is subject to generating thermal & shot noise but these are very small.

Are you refering to a normal mode or a common mode choke? How well they work as a filter depends on the frequency of operation among other things. The choke/inductor typically looks inductive over a range of frequencies (may be narrow or large) until it becomes capacitive looking at some sufficiently high frequency. If you build a single pole filter(for example) with one of these, it will only be effective over the range of frequencies that the inductor/choke looks inductive.

IF the filter is normal mode, it will filter normal mode signals (including noise). By how much it attentuates the noise is a function of the inductor values & number of poles in the filter.

Normal mode filters do not filter common mode signals and vice-versa.

 

would inductors make noise if you put two near each other? and how do you put dc throught a choke if a choke is two inductors wired onto one core or am i thinking of somthing else, if so what is a choke?

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when you post that reply, im just kidding.

 

I've tried to find a relatively precise definition of a choke but without much success. A choke is a specific kind of inductor. A choke, like other inductors, is usually described by it's inductance, among other characteristics. A choke is often used to filter or block AC and pass DC where the AC, noise or non-DC component is thrown away -for lack of a better description. Sometimes inductors are used to store power or create a resonant circuit - or when put close together there is coupling and a transfer of power. In these cases we don't "throw" away the AC - so it would seem the inductor characteristics would be such that the AC is returned efficiently. This is the best I can do. I too am interested in a better definition of choke.

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stevez

 

The way I use the term "Choke" is when the inductor is a (significant) current-carrying inductor.

Not an inductor in a tuned cct or small-signal stuff but in big power supplies (say and amp or so) where it's presence "chokes" the change in flow of current

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Two inductors on a core together are a transformer because they are coupled together and transfer an AC signal.

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True.
A common mode choke has the same configuration. It actually acts as a transformer for differential signals, with the flux from each side cancelling that of the other, which makes the common-mode choke "invisible" (ideally) to differential-mode signals. When you see coax making a turn or two through a toroid, that's also common-mode choke.

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Ron

 

Choke is nothing but inductor. It's inductance is causing reactive resistance to AC currents.
XL=w*L
If you place it in series with your load it will attenuate signals with unwanted frequencies to pass your load. It will not block them but only attenuate. Higher is the frequency higher is the attenuation up to frequencies where the parasitic capacintance of choke starts to play a role.
Choke filter can be made a single coil or double coil. Double coil filter can be connected in two ways. One way is when we want to attenuate common mode interfearing signals and other is for differential signals. Double coil filter has its coils connected in both wires live and common or in positive and in negative supply wires.

 

As 'bloki' says, a choke is nothing but another name for an inductor, as suggested throughout this thread it's more commonly applied to power inductors used in power supplies (particularly the HT smoothing choke in a valve amplifier). However, it's also commonly applied to much smaller inductors, how many of you have heard of 'RF chokes'?, a very commonly used component in the past.

I would suggest that perhaps a choke is an untuned inductor?, whereas an inductor itself would most commonly be tuned?.

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Tuning relates to resonator. It can be done with capacitor or inductor.

 

It's done with BOTH, a choke normally wouldn't be tuned, except by it's own low self capacitance, but it's not really significant.

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Okay, thank you all for the answers..

Quote:
The small series resistance of the conductor is subject to generating thermal & shot noise but these are very small.

==>I have a schematic below that draw the inductor equivalence circuit below.. it has an equivalence series resistor inside an inductor and also a capacitor, is it right? please tell me how do the shot noise occur in the inductor, i read from a book and it said that the "shot noise is a random fluctuation that accompanies any direct current crossing a potential barrier. The effect occurs because the carriers (holes and electrons in semiconductor) do not cross the barrier simultaneously, but rather with a random distribution in the timing for each carrier, which gives rise to a random component of current superimposed on the steady current. the name shot noise was first coined in connection with tubes, where the analogy was made bertween the electrons striking the plate and lead shot from a gun striking a target." so, please tell me how could the shot noise occurs in the inductor since there are no barrier/pn junction inside the inductor? is it any other definitions about shot noise?

==>i have two schematic below, one is use the choke filter, another one only use the capacitor as a filter, when we use the choke filter/inductor as a filter, the output drop, it must be caused by inductive reactance (XL = 2.pi.f.L), right? please tell me what is the small fluctuation in the output signal of the choke filter? is it the thermal noise n the shot noise? when we use the capacitor as the filter, the noise doesn't occured in the output signal (please look at schematic below), so, is it mean that the inductor also cause the noise to the circuit? if the capacitor is better than the inductor since it doesn't have the output drop, and also don't have any noise in the output signal, why should we use the choke filter for example in switching mode power supply design?

==> what is the meaning of normal mode choke? and the common mode choke?

==>what is the meaning by number of poles in the filter?

Thank you very much

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SHot noise was the wrong term (sorry!) Resistive conductors carry thermal noise and "Excess" noise similar to shot noise (proportional to the current flowing through them. The excess noise is noise in addition to the thermal which can have a 1/f spectrum. See "flicker" noise for this type of noise.

These sources of noise are indsignificant in your application. I wouldnt worry about them at all. The noise you are talking about is more related to ripple voltage/current than small signal noise sources.

If you think the noise is gone because you used capacitor instead of inductor, try again. In your capacitor, look at the current through it.
In a real capacitor, an equivalent series resistance will convert the ripple current into a ripple voltage.

Number of poles in a filter is a frequency domain concept. If you write the transfer function of your filter in the frequency domain say, Vout(s) / Vin (s) and you find the values that make the denominator = zero, those are poles. The number of these values is equal to the number of poles.