choke filter - Page 2 - Electronic Circuits Projects Diagrams Free

Optikon · 7th November 2005, 02:27 PM

Quote:

Originally Posted by zhi_yi

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

What do you mean why use in switching mode design? You show a crude linear power supply design. In this design, your noise will be related to 120Hz components due to the full wave rectification. It will be reduced by your two pole filter (L & C). Diodes in this circuit produce shot noise & negligible thermal noise. Load resistor produces thermal and excess noise. Purely reactive parts of L & C producce no noise. BUT all of these noise sources are swamped out by 120Hz ripple component by many orders of magnitude.

The way your choke is shown, implies a normal mode choke. A common mode choke would filter only signals common to both your supply rail & ground rail & would be shown with a different symbol. I dont think you need concern yourself with it based on the example you are experimenting with.

Roff · 7th November 2005, 04:55 PM

In this copy of your scope shot (below), if you think the aberrations that I have circled are noise - they're not. They are quantization artifacts of your instrument if this is from an oscilloscope, or from your computer or monitor if this is a simulation (which I think it is).
As Optikon pointed out, thermal noise in an inductor is the least of your worries when you are making a power supply. In my 40+ years as an engineer, I have never heard the subject mentioned, in any circuit application.

zhi_yi · 8th November 2005, 03:02 AM

okay.. thank you very much.. :)

so, the 1/f noise is also called as excess noise?

quote:
What do you mean why use in switching mode design?

i am sorry, in the previous message, i mean in switching mode power supply design (SMPS) ..

can you please give me a simple schematic example of common mode choke filter..?

what is the meaning of quantization artifacts? i simulate the circuit with a software (multisim) :) i just want to know, because i heard from my lecturer, he said that inductor is the source of noise.. so i try to simulate it in the simulation software to find out which one work better as a filter, and i see the abberation if i use inductor, so i think it's the noise.. i am sorry... hehe.. :)

Roff · 8th November 2005, 04:52 AM

Quote:

Originally Posted by zhi_yi

okay.. thank you very much..

so, the 1/f noise is also called as excess noise?

quote:
What do you mean why use in switching mode design?

i am sorry, in the previous message, i mean in switching mode power supply design (SMPS) ..

can you please give me a simple schematic example of common mode choke filter..?

what is the meaning of quantization artifacts? i simulate the circuit with a software (multisim)

i just want to know, because i heard from my lecturer, he said that inductor is the source of noise.. so i try to simulate it in the simulation software to find out which one work better as a filter, and i see the abberation if i use inductor, so i think it's the noise.. i am sorry... hehe..

Regarding quantization artifacts:
Here are two plots of the exact same sine wave, plotted on different scales. Notice the increased visibility of steps in the bottom plot. The voltage source being plotted has no steps. I simulated this on Linear Technology's SwitcherCAD III, but the results will look the same on almost any simulator. The vertical drafting resolution is not very good. The waveshape gets quantized (digitized) by the limits of the plotting software and, to a lesser extent I think, the hardware (the raster on your monitor).
If you were to zoom in on that noisy portion of your simulation (before you save it as a graphic), the noise would go away.

Optikon · 8th November 2005, 01:38 PM

Quote:

Originally Posted by zhi_yi

okay.. thank you very much..

so, the 1/f noise is also called as excess noise?

quote:
What do you mean why use in switching mode design?

i am sorry, in the previous message, i mean in switching mode power supply design (SMPS) ..

can you please give me a simple schematic example of common mode choke filter..?

what is the meaning of quantization artifacts? i simulate the circuit with a software (multisim)

i just want to know, because i heard from my lecturer, he said that inductor is the source of noise.. so i try to simulate it in the simulation software to find out which one work better as a filter, and i see the abberation if i use inductor, so i think it's the noise.. i am sorry... hehe..

I'd recommend you forget about excess, shot, 1/F noise & all such things for what you are working on. These are not part of what you are seeing in your plots. I think you caused much confusion about your original question of an inductor causing noise. They don't in the strictest sense but your circuit does! or your measurement does! and that's what we are really talking about here. Read this for a first hit google example on common mode chokes.

http://www.butlerwinding.com/inductors/common_mode.html

Dont confuse this with the other sources of intrinsic noise talked about earlier. I doubt your instructor believes that inductors can _source_ noise. Where would the energy come from? Your circuit causes noise! Energy source is from your 60Hz generator. Having both and L and C in your circuit is better (noise-wise) than having just a single L or a single C. You have a two pole filter instead of one pole.

**Nigel Goodwin** · 8th November 2005, 01:44 PM

Perhaps it would be an idea to tell us EXACTLY what you are trying to do?, if it's simply that you're playing with a simulator, then you're probably wasting everyones time (including your own).

However, if you're trying to design a 1950's (or 30's or 40's) valve power supply, then you're also wasting your time with such questions about noise.

zhi_yi · 9th November 2005, 10:22 AM

okay thank you very much

i am sorry for wasted everyones time

i just want to know is it right that the inductor source noise, and i try to simulate a circuit with the inductor, so, i choose a simple power supply circuit for compare is it true that inductor is the source of noise.. okay.. thank you all

Optikon · 9th November 2005, 12:26 PM

Quote:

Originally Posted by zhi_yi

okay thank you very much

i am sorry for wasted everyones time

i just want to know is it right that the inductor source noise, and i try to simulate a circuit with the inductor, so, i choose a simple power supply circuit for compare is it true that inductor is the source of noise.. okay.. thank you all

You havn't wasted my time, I choose to waste my own time. :lol:

I fyou want to study noise of individual components, you will need to setup a noise simulation with proper modelling. The power supply is a poor choice because it overcomplicates things. All you need for a simple noise simulation is a generator and a component. If you study up on noise theory, you will find that pure reactances do not exhibit intrinsic noise sources, so why would you think a simulation would show one? If the sim did, I would believe it to be incorrect.

zhi_yi · 10th November 2005, 02:49 PM

okay opticon.. thank you..

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8th November 2005, 03:02 AM	(permalink)
zhi_yi	okay.. thank you very much.. :) so, the 1/f noise is also called as excess noise? quote: What do you mean why use in switching mode design? i am sorry, in the previous message, i mean in switching mode power supply design (SMPS) .. can you please give me a simple schematic example of common mode choke filter..? what is the meaning of quantization artifacts? i simulate the circuit with a software (multisim) :) i just want to know, because i heard from my lecturer, he said that inductor is the source of noise.. so i try to simulate it in the simulation software to find out which one work better as a filter, and i see the abberation if i use inductor, so i think it's the noise.. i am sorry... hehe.. :)

8th November 2005, 01:44 PM	(permalink)
Nigel Goodwin	Perhaps it would be an idea to tell us EXACTLY what you are trying to do?, if it's simply that you're playing with a simulator, then you're probably wasting everyones time (including your own). However, if you're trying to design a 1950's (or 30's or 40's) valve power supply, then you're also wasting your time with such questions about noise. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

9th November 2005, 10:22 AM	(permalink)
zhi_yi	okay thank you very much i am sorry for wasted everyones time i just want to know is it right that the inductor source noise, and i try to simulate a circuit with the inductor, so, i choose a simple power supply circuit for compare is it true that inductor is the source of noise.. okay.. thank you all

10th November 2005, 02:49 PM	(permalink)
zhi_yi	okay opticon.. thank you..