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Capacitors - more active than you think

MikeMl

Well-Known Member
Most Helpful Member
Your link doesn't work
 

KeepItSimpleStupid

Well-Known Member
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Thanks Mike. Works now. The auto-URL function included the next word because I didn't insert a space. Worked as expected, but it can't read minds.
 

misterT

Well-Known Member
Most Helpful Member
That is a good article, but I don't like the style of it. Weird sentences like this:
Meanwhile, we call components like capacitors, resistors, inductors, connectors, and even the PC board (PCB) passive because they do not seem to consume power.
All passive components change the signal. Resistors can act like attenuators. Inductors and Capacitors store and release energy, they are reactive components. I think that transistors differ from passive/reactive components in a way that their behavior depends from more than one signal/variable. They can not be presented as lumbed element with one input and one output, or with two variables; one across the component and one through the component.

The Topic of the article should be something about parasitic components. I don't know why they choose to go with "Passives Aren’t Really So Passive".. I think that is strange way to talk about parasitics of passive components.
 

MikeMl

Well-Known Member
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How is it that a passive resistor does not consume power?
 

sakiz

New Member
@KeepItSimpleStupid: Thanks for sharing the link. It is quite interesting that the writer has given their view about why the capacitor is not a passive component. They mentioned that these components don't consume power...which is quite interesting as Power (P) = Voltage drop (V)*Current (I) and you can always measure voltage and current across any passive component. Power could be calculated by using this formula. Now how did these passive parts not consume power? And looks like all the posters are and will be around this sentence as Roff said.
 
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unclejed613

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yeah, i thought the same thing "waddya mean passive components don't consume power?....... actually passive components don't have voltage or current CONTROLLED elements in them. with that definition, any semiconductor, even if it only has 2 terminals, is an active component. an inductor with a saturable iron core kind of rides the fence between active and passive.... at least that's always the way i've looked at it......
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

Yeah, that's the very very first time i ever saw any site claim that resistors do not consume power, and not only once, but they state that twice. Very unusual. Someone messed that writing up :)

"Conversely, passive components like resistors, capacitors, inductors, and connectors do not consume power—or so we like to assume."

I dont know anyone who "likes" to assume this <chuckle, chuckle, chuckle>

" Meanwhile, we call components like capacitors, resistors, inductors, connectors, and even the PC board (PCB) passive because they do not seem to consume power."

Yeah they dont seem to consume power in a universe in which all sub atomic particles have different properties. Too bad we all live in this universe ha ha.

So someone messed up writing that <big big chuckle>

Hey, it's good to get a laugh in now and then anyway :)

But then again they forgot to mention that we "like" to assume that wire does not consume power either. Since they wanted to include everything, maybe they should have worded it like this instead:
"Nothing seems to consume power"
har har har :)
 
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Roff

Well-Known Member
I sent Maxim an email. I'm sure they will get a boatload of comments on that statement.
I received this reply from Maxim:
The following is a response to your post on the Maxim website.
|
|================================================================
|
| Subject : Re: Passives Aren’t Really So Passive: Part 1, Capacitors
| To : address deleted
| Sender : bill.laumeister@maximintegrated.com
| Location:
| http://www.maximintegrated.com/app-notes/index.mvp/id/5663
|

Roff,
First, this sentence is poorly written. We also received comments inside Maxim on this sentence. the internal discussion went from adding, "(while creating gain) like semiconductors.” to what is probably better, replacing "consume" with "control". The sentence then is "we call components . . . passive because they don't seem to control power". What do you think?

|
| Maxim Home Page:
| http://www.maximintegrated.com/
 

misterT

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Most Helpful Member
"we call components . . . passive because they don't seem to control power"
Doesn't that imply that passive electronics do control power? Isn't the word "control" more appropriate for active components?
 

MrAl

Well-Known Member
Most Helpful Member
Hi,


I would opt for a rewrite where we bypass the passive/active element argument altogether because that gets quite sticky really fast. A transformer for example seems to be passive yet we can add control windings.

Rough example:

"We normally dont think of some elements as being capable of dissipating power when in real life they almost always do."
 
This Maxim article is a joke to say the least. The fact that L & C can store energy then later deliver energy to the outside world does not make them "active". An active device has power gain, such as a bjt, FET, op amp, etc., whereas a passive device does not. A transformer can only output a power just under that which is inputted. The said xfmr has leakage inductance which stores energy which can be released to outside world. But it is a passive device.

It's all about definitions. A moped is a good example. With fuel in the tank, a small effort by the driver results in power to move the vehicle greater than driver effort, or power gain >> 1. Once the tank is empty, the power is generated entirely by driver, power gain is just under unity. Here the vehicle is passive since gears, chains, etc. are "passive" parts.

An IC engine is active, but a gear is passive. But using Maxim rhetoric "is a gear really passive"? Take a heavy gear, drop it from a 15 story building, and nobody I know wants it to land on their head. But does this mean that a gear is "really" an "active" part?

I think not. Maxim is really desperate to publish something these days. I have past articles from them that are quite good. But this is sophomoric claptrap. It's an embarrassment to Maxim and any publication which prints this nonsense. We define active vs. passive parts using what I believe to be good criteria. The fact that a charged cap can deliver a lethal shock is worth knowing. When I call a cap "passive" I am not overlooking this fact. Passives deliver less output power than the input power, except for a brief moment when they give up energy stored in their electric and/or magnetic fields.

Unbelievable. Does anybody take this article seriously? I never thought I'd see the day where such crap is published by a prominent company.
 
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Roff

Well-Known Member
This Maxim article is a joke to say the least. The fact that L & C can store energy then later deliver energy to the outside world does not make them "active". An active device has power gain, such as a bjt, FET, op amp, etc., whereas a passive device does not. A transformer can only output a power just under that which is inputted. The said xfmr has leakage inductance which stores energy which can be released to outside world. But it is a passive device.

It's all about definitions. A moped is a good example. With fuel in the tank, a small effort by the driver results in power to move the vehicle greater than driver effort, or power gain >> 1. Once the tank is empty, the power is generated entirely by driver, power gain is just under unity. Here the vehicle is passive since gears, chains, etc. are "passive" parts.

An IC engine is active, but a gear is passive. But using Maxim rhetoric "is a gear really passive"? Take a heavy gear, drop it from a 15 story building, and nobody I know wants it to land on their head. But does this mean that a gear is "really" an "active" part?

I think not. Maxim is really desperate to publish something these days. I have past articles from them that are quite good. But this is sophomoric claptrap. It's an embarrassment to Maxim and any publication which prints this nonsense. We define active vs. passive parts using what I believe to be good criteria. The fact that a charged cap can deliver a lethal shock is worth knowing. When I call a cap "passive" I am not overlooking this fact. Passives deliver less output power than the input power, except for a brief moment when they give up energy stored in their electric and/or magnetic fields.

Unbelievable. Does anybody take this article seriously? I never thought I'd see the day where such crap is published by a prominent company.
Excellent, Claude!
You should consider sending this verbatim to Bill Laumeister at Maxim. I posted his email address in post #10. Here it is again: bill.laumeister@maximintegrated.com
Bill had replied to me after my critique of the article.
 

Bill Laumeister

New Member
Great comments, I just had someone send me a link today. As engineers we should discuss things, so we all can learn. Any article that sparks this kind of discussion is good. One problem of writing an article is 1500 words is not enough to explain things in detail. For example, we see IC datasheets that say place a 0.1uF decoupling capacitor near the power pin. But we never see that the other side of the capacitor needs to be near to ground.

I'm still trying to find a short definition of passives. The most common definition is “not active”. A typical active device uses power to do something like create gain. The point of the articles are to tell people that what we think is a passive can and does cause non linear responses that can change the signal. Such as, resistor voltage dependence or capacitive absorption (soakage) causing harmonic distortion or hydroscopic printed circuit boards changing offset. How do you define a passive component?
 

The Electrician

Active Member
Great comments, I just had someone send me a link today. As engineers we should discuss things, so we all can learn. Any article that sparks this kind of discussion is good. One problem of writing an article is 1500 words is not enough to explain things in detail. For example, we see IC datasheets that say place a 0.1uF decoupling capacitor near the power pin. But we never see that the other side of the capacitor needs to be near to ground.

I'm still trying to find a short definition of passives. The most common definition is “not active”. A typical active device uses power to do something like create gain. The point of the articles are to tell people that what we think is a passive can and does cause non linear responses that can change the signal. Such as, resistor voltage dependence or capacitive absorption (soakage) causing harmonic distortion or hydroscopic printed circuit boards changing offset. How do you define a passive component?
You might consult the IEEE dictionary:

http://www.amazon.com/IEEE-Standards-Dictionary-Glossary-Definitions/dp/0738157392/ref=sr_1_4?s=books&ie=UTF8&qid=1383790316&sr=1-4&keywords=IEEE+dictionary

Also, this Wikipedia article is good; reference 2 is quite detailed:

http://en.wikipedia.org/wiki/Passivity_(engineering)

It would appear that resistors, capacitors, inductors and transformers are both thermodynamically and incrementally passive.
 

crutschow

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Most Helpful Member
yeah, i thought the same thing "waddya mean passive components don't consume power?....... actually passive components don't have voltage or current CONTROLLED elements in them. with that definition, any semiconductor, even if it only has 2 terminals, is an active component. an inductor with a saturable iron core kind of rides the fence between active and passive.... at least that's always the way i've looked at it......
I think a saturable core amplifier is definitely active since it certainly controls power. Also a device, such as a carbon mic, which amplifies the audio signal (as opposed to a dynamic or crystal mic which does not) I would consider an active device. (It's interesting that early long distance telephone lines used carbon mic repeaters to periodically amplify the signal along the way before electronic amplifiers were invented).
 

misterT

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Most Helpful Member
I have to comment my own post. (post #11)
"we call components . . . passive because they don't seem to control power"
I think that the use of the word "seem" implies that there is "but" coming. If somebody uses the word "seem", I think it means that the author disagrees what is being said (what is the general consensus).

If I have a flower and I confidently say (being a flower expert): "the flower seems to be blue"
Everybody will think that the flower is not blue.. it just seems to be blue.
 

Bill Laumeister

New Member
The Electrician had good suggestions, Amazon’s delivery on the IEEE dictionary is 1 to 2 MONTHS, so I bought a used one for $180, but it won’t get here until next week. The Wikipedia entry [ http://en.wikipedia.org/wiki/Passivity_(engineering) ] has an interesting perspective in the first two paragraphs;

“Passivity is a property of engineering systems, used in a variety of engineering disciplines, but most commonly found in analog electronics and control systems. A passive component, depending on field, may be either a component that consumes (but does not produce) energy (thermodynamic passivity), or a component that is incapable of power gain (incremental passivity).

A component that is not passive is called an active component. An electronic circuit consisting entirely of passive components is called a passive circuit (and has the same properties as a passive component). Used without a qualifier, the term passive is ambiguous. Typically, analog designers use this term to refer to incrementally passive components and systems, while control systems engineers will use this to refer to thermodynamically passive ones.”

Then depending on one’s engineering discipline;

“Thermodynamic passivity
In control systems and circuit network theory, a passive component or circuit is one that consumes energy, but does not produce energy. Under this methodology, voltage and current sources are considered active, while resistors, capacitors, inductors, transistors, tunnel diodes, glow tubes, metamaterials and other dissipative and energy-neutral components are considered passive.”

“Incremental passivity
In circuit design, informally, passive components refer to ones that are not capable of power gain; this means they cannot amplify signals. Under this definition, passive components include capacitors, inductors, resistors, diodes, transformers, voltage sources, and current sources. They exclude devices like transistors, vacuum tubes, relays, tunnel diodes, and glow tubes.”

Wow, I can’t wait to see what the IEEE dictionary says. The Wikipedia article really sums it up in the second paragraph, “Used without a qualifier, the term passive is ambiguous.” Which crutschow perfectly illustrates with the “saturable core amplifier” and “carbon mic as an amplifier”. MisterT rightly dings me for using “seems”, I was trying to “weasel word” the definition to allow non-linear distortion from something we expect to be “inert” or “benign”.

I know “inert” or “benign” will probably add fuel to the fire.
 

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