How to wrap a inductor around a resistor on PCB?

ronsimpson

Joined Oct 7, 2019
2,078
Do you have a picture?
This inductor on a resistor trick is common in RF circuits for armature radio. KiCad only sees the resistor and does not know you added wire.
1648073359505.png
 

Ian0

Joined Aug 7, 2020
5,155
Why do you think it is a good idea to wind an inductor around a resistor? Do you know how much ferromagnetic material is in the resistor?
 

ronsimpson

Joined Oct 7, 2019
2,078
KiCad sees it as a resistor.
I do not know what is best.
You can make the R and L have the same size part and put them in the same place.
You can just not add the L to the PCB. (set if off the edge of the board)
You can make a special schematic part which looks like F32 and L1 at the same time as one part.
 

Thread Starter

Sirbroccoli

Joined Feb 21, 2020
8
KiCad sees it as a resistor.
I do not know what is best.
You can make the R and L have the same size part and put them in the same place.
You can just not add the L to the PCB. (set if off the edge of the board)
You can make a special schematic part which looks like F32 and L1 at the same time as one part.
I see, i thought there is a special way to do it. I will try one of these, thanks for the reply.
 

nsaspook

Joined Aug 27, 2009
9,740
Why do you think it is a good idea to wind an inductor around a resistor? Do you know how much ferromagnetic material is in the resistor?
1648089786396.png
The inductance value not particularly important is most applications (deliberately make a poor (low-Q) inductor for parasitic suppression) where this is done for a high current out-of-band filtering component (like a Zobel network). The resistor is usually a carbon composition resistor to reduce magnetic effects from the coil form.


Usually a note is indicated on the schematic for the component for the proper size/value/composition of the resistor and gauge of wire with number of turns.

https://www.embedded.com/matching-and-tuning-audio-amplifier-output-stability-and-sound-performance/

1648091006551.png
A usual output network called “Zobel” for a power amplifier with typical component value is shown in Figure 8 below. All kinds of output network have only one purpose – it is to improve the stability. This recommended network Zobel contains a resistor and a capacitor in series from the amplifier output to ground. The resistor is for limiting the current on a certain higher frequency to reduce the capacitor rating requirement. Approximate resistor value range is from 4.7 to 10 ohms.
...
The frequency response of a real loudspeaker speaker shows uneven impedance load as the series combination of the amplifier output impedance and cable resistance and inductance. It could cause high frequency instability.

Adding a small coil inductor in series with the amplifier output increases the instability. It isolates the amplifier from the shunt capacitor without causing significant loss at the audio frequencies.The inductor value normally ranges from 1 to 7 microHenrys. A suitable value can be set to avoid high frequency roll-off at a certain loading impedance.

The air-cored inductor is recommended to eliminate the possibility of magnetic saturation. A damping resistor across the output coil is also recommended to reduce the Q factor of the output LC network,overshooting and ringing.
 
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Ian0

Joined Aug 7, 2020
5,155
The purpose of the inductance is to prevent the load looking capacitive at high frequencies due to high-pass crossover networks or piezoelectric tweeters, but if the load impedance seen by the amplifier continues to rise at high frequencies, and the amplifier is unstable. The parallel resistor limits the amount of impedance rise.
Doug Self has a chapter in his power amplifier book on Zobel networks.
The Thiele impedance stabilising network is a more comprehensive circuit, which probably does require an accurate inductance, especially when repurposed by Cherry in his NDFL amplifiers.
By the way, does anyone have a copy of Thiele's paper?

As for the original question - just put the resistor in Eeschema, and add a note that it has n turns of whatever gauge wire wound around it.
 

du00000001

Joined Nov 10, 2020
100
IMHO this is a huge misunderstanding of the article referenced:
  • "wirewound resistor" is about the buildup of the resistor ("wound of wire") - the usual technology to build low-Ohm resistors with a significant power rating. (See also post #7.)
    Another technology would be to use a "carbon mass" resistor - if you still can get one.
  • There's no need to wind the coil on the resistor's body - you can easily place it somewhere parallel to the resistor. (BTW: my experience is that the leads of resistors are often magnetic - maybe due to some nickel layer applied to stop diffusion.
 

nsaspook

Joined Aug 27, 2009
9,740
IMHO this is a huge misunderstanding of the article referenced:
  • "wirewound resistor" is about the buildup of the resistor ("wound of wire") - the usual technology to build low-Ohm resistors with a significant power rating. (See also post #7.)
    Another technology would be to use a "carbon mass" resistor - if you still can get one.
  • There's no need to wind the coil on the resistor's body - you can easily place it somewhere parallel to the resistor. (BTW: my experience is that the leads of resistors are often magnetic - maybe due to some nickel layer applied to stop diffusion.
Huge misunderstanding? This is about building a specialized component, there is no misunderstanding.
 

du00000001

Joined Nov 10, 2020
100
Huge misunderstanding? This is about building a specialized component, there is no misunderstanding.
This "specialized component" can be considered snake oil. Or electronic voodoo. A bit like oxygen-free copper and gilded connectors (the latter make at least sense in case you need repeatable (but limited) plugging/unplugging cycles).
 

nsaspook

Joined Aug 27, 2009
9,740
This "specialized component" can be considered snake oil. Or electronic voodoo. A bit like oxygen-free copper and gilded connectors (the latter make at least sense in case you need repeatable (but limited) plugging/unplugging cycles).
That's total BS, this is not snake oil, it's circuit engineering with a proper mathematical foundation. It's a hardware hackers way to combine 2 needed components in a “Zobel” or other network into one component. Wire coil wrapped resistors have be used in amplification equipment forever (from the tube era). Look at R5253/L5201 and similar for examples of inductor/resistor combinations on audio amplifier outputs.

1648243297349.png
Panasonic SA-AK630
 
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du00000001

Joined Nov 10, 2020
100
That's total BS, this is not snake oil, it's circuit engineering with a proper mathematical foundation. It's a hardware hackers way to combine 2 needed components in a “Zobel” or other network into one component. Wire coil wrapped resistors have be used in amplification equipment forever (from the tube era). Look at R5253/L5201 and similar for examples of inductor/resistor combinations on audio amplifier outputs.
I only accept these coil wrapped resistors if you can tell me how to implant a resistor into a capacitor (e.g. C5443 / R5450) !
if the former is real, the latter will be the next challenge. Or should we somehow implement a capacitor on the outer surface of the resistor ?

Honestly! - what exactly do you know about electronics ?
 

nsaspook

Joined Aug 27, 2009
9,740
I only accept these coil wrapped resistors if you can tell me how to implant a resistor into a capacitor (e.g. C5443 / R5450) !
if the former is real, the latter will be the next challenge. Or should we somehow implement a capacitor on the outer surface of the resistor ?

Honestly! - what exactly do you know about electronics ?
Honestly! I don't really care what you think as it's pretty obvious at this point you know nothing about the subject, as the inductor around a resistor is a circuit physical (PCB, point to point, etc...) construction detail, not one designed for special electrical properties. Thanks for your input.
As for implanting a resistor into a capacitor on a semiconductor substrate, understanding how to do that is part of my job. ;)
https://inst.eecs.berkeley.edu/~ee105/fa03/handouts/lectures/Lecture7.pdf
 
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Ian0

Joined Aug 7, 2020
5,155
I only accept these coil wrapped resistors if you can tell me how to implant a resistor into a capacitor (e.g. C5443 / R5450) !
if the former is real, the latter will be the next challenge. Or should we somehow implement a capacitor on the outer surface of the resistor ?

Honestly! - what exactly do you know about electronics ?
You can buy combined resistors and capacitors
https://uk.farnell.com/cornell-dubilier/104m06qc100/cap-0-1-f-20/dp/2841754?st=snubber
 

prepka

Joined Oct 5, 2020
20
Why do you think it is a good idea to wind an inductor around a resistor? Do you know how much ferromagnetic material is in the resistor?
A carbon composition resistor doesn't have any ferromagnetic material and the R32 size refers to the old carbon comp size for a half watt resistor. It is used as a bobbin form to make coil on. Metal film and..metal oxide resistors are also not magnetic. The inductance comes from the number of turns and coil diameter and width in free air as you are creating an air wound coil. If you are interested, you can look up the formula for this since it is an air core inductor.
 
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