When do I use capacitors?

Thread Starter

Sulvek

Joined Aug 27, 2022
20
Hello all! Yes I know this is the most basic question ever. When I ask things like this I get replies saying I should learn the basics before hand but that's exactly what I'm trying to do here. I have played around a lot with projects and often I find multiple schematics to do the same exact project. It confuses me because some of these schematics will use capacitors and some won't. It will be the same circuit but depending who made the schematics they decide whether or not to use a capacitor. It seems to me if it works without one why do some people include it? I work in HVAC. My job does not require me to actually know anything about capacitors though. My idea has always been that they hold lots of magic to be used for things that need extra magic. Like I said please don't call me out for my lack of knowledge because it isn't helpful. I have watched many youtube videos and just can't find info on when to use the puppies. I just need a point in the right direction. If you know of any good reading material that would be great to. Thanks a lot guys and gals!
 

Thread Starter

Sulvek

Joined Aug 27, 2022
20
Like any project, It all depends on the application design etc , as it is with any circuit device.
https://www.eeweb.com/capacitor-characteristics-and-features/
I understand that but how do I look at a circuit and know if it requires a capacitor or could use a capacitor to improve it? My aim is to be able to make my own circuits and not just follow what someone else has done. I have done lot's of projects but just don't learn anything from them. It's like looking at a picture and just making a copy. It has helped get down some of the basics but to create circuits from scratch I need to understand how and when I need caps.
 

MrSalts

Joined Apr 2, 2020
2,354
In most cases you'll see,
1) the capacitors store some electric power near the logic chips and amplifier chips that convert signals in case there are any blips or dips in the power to the chips (whether from the main power source or from current draw caused by other parts of the circuit board or the resistance of the circuit board traces itself).
2) capacitors are used to filter signals. If, for example,a 10kHz signal is transmitted or not transmitted, and you don't care about lower or higher frequencies, you can create filters with capacitors and resistors to clean up any data line that is below or above 10kHz
3) capacitors can be used to make timing devices and oscillators that measure time or create a repeating pulse (clock)
Others are possible and I'm sure to be corrected now that I started to answer your question.
 

crutschow

Joined Mar 14, 2008
30,788
Capacitors can do many different things, depending the application.
Below are those I thought of:
  • Filter a DC supply voltage by connection between the supply and ground/common. This helps remove noise and voltage fluctuations to prevent circuit malfunction from those variations.
  • Filter the output of a AC voltage powered rectifier to get a smooth DC supply voltage.
  • Block DC bias voltages in a circuit so allow the transfer of an AC signal voltage with affecting the DC bias.
  • Use in conjunction with resistors or inductors to provide a filter function (reject or pass particular signal frequencies).
  • Use with an inductor to provide a resonant oscillation at a specific frequency.
So determining when to use a capacitor is all part of circuit design.
You also need to understand how resistors and inductors work, as well as active devices, to do the total process.
 

Papabravo

Joined Feb 24, 2006
19,284
Capacitors are seldom used in isolation. If you study circuits that use capacitors in various ways you will see both how they are used and why they are used. I don't know how to tell you to do this because I can't remember how I did it except by watching what other people did and asking them why. Over time this knowledge becomes assimilated.
 

dl324

Joined Mar 30, 2015
15,112
It confuses me because some of these schematics will use capacitors and some won't. It will be the same circuit but depending who made the schematics they decide whether or not to use a capacitor.
Capacitors have multiple uses. Without knowing which application you're referring to, no one can give you a reasonable answer.

Note that decoupling capacitors aren't always shown, but it's assumed you know that most circuits will require them for reliable operation. Note the use of "reliable". How do you know that a circuit with omitted capacitors is operating reliably?
It seems to me if it works without one why do some people include it?
Possibly because the person who designed the circuit knows more than you.
I just need a point in the right direction.
The topic is too broad. We need a specific example.
 

WBahn

Joined Mar 31, 2012
27,392
Unfortunately, now matter how many times you say you don't want to be told to learn the basics, the problem is that you need to learn the basics. How can you possibly hope to learn how to use capacitors when you describe your knowledge of what a capacitor is as something that "holds lots of magic".

As others have said, capacitors serve many different purposes in circuits and we really need to see specific examples of schematics you are talking about.

Having said that, the most likely use that you are seeing (i.e., when you see comparable schematics in which one has caps that the other doesn't) are decoupling capacitors used to stiffen the power supplies locally in a circuit. Many schematics focus on just the signal processing components and leave it to the person implementing the circuit to deal with proper decoupling. In part this is to keep the schematic clean, but also it is because the number, value, and type of capacitors to use is less a function of the schematic circuit and more a function of the physical layout of the circuit as actually implemented. Then, too, there are the ton of schematics that are made by people that are ignorant of the whole issue of proper decoupling and they are left out for that reason.

After doing a Google search for "capacitors" to learn what a capacitor is and the various applications for them, do a Google search for "decoupling capacitors" to focus more on this particular application. Wikipedia is a good place to start.
 

MrChips

Joined Oct 2, 2009
27,117
It is the same question as “When do I use a …
  1. resistor
  2. capacitor
  3. inductor
  4. diode
  5. transistor
  6. fuse
  7. wire
  8. relay
  9. battery
  10. DPDT switch
  11. transformer
  12. etc., etc.,
  13. etc.

A capacitor has multiple functions based on its behaviour in all kinds of electrical circuits. We can list them all in a very long list of applications.
You need to learn the basic properties of capacitors in DC and AC circuits. There is no shortcut to learning about capacitors.
 

Thread Starter

Sulvek

Joined Aug 27, 2022
20
Got all the expected None helpful toxic ego pumping love letters reminding me to learn what a capacitor is before asking what a capacitor is. Besides that I did get some crazy good replies that helped a lot and were exactly what I needed. A point in the right direction. The problem with learning is that when starting out we may not know enough to ask the right questions. Now I know how to ask better questions and actually get results on google and youtube. Thanks a lot guys!
 

StrongPenguin

Joined Jun 9, 2018
301
Got all the expected None helpful toxic ego pumping love letters reminding me to learn what a capacitor is before asking what a capacitor is. Besides that I did get some crazy good replies that helped a lot and were exactly what I needed. A point in the right direction. The problem with learning is that when starting out we may not know enough to ask the right questions. Now I know how to ask better questions and actually get results on google and youtube. Thanks a lot guys!
I'd suggest not calling people toxic, if you seek their help. Been a newbie member here for some years now, and I have always received great inputs from all the knowledgeable and helpful members here.

I can understand your frustration on learning electronics, and caps. It's not an easy hobby to take up, IMO. I am still very much a newbie, but what has helped me the most is building a circuit, and then picking it apart again, changing values on caps, resistors and what not, just to see how it behaves, while having my oscilloscope and multimeter hooked up.

If you don't own these tools, nor plan to, but you just want to understand it from a "user" perspective (maybe related to HVAC control boards?), then the answers given should be enough to scratch the surface. But if you want to dig deeper, it is best to cover the basics by reading material about caps, and what not. Build a few circuits, remove some caps, see what happens.
 
Last edited:

Ian0

Joined Aug 7, 2020
6,293
Why don’t you post a couple of the schematics you’ve been looking at, and we’ll tell you why capacitors have been used and what they do?
 

DickCappels

Joined Aug 21, 2008
9,317
Early in my career I would leave out "extra parts", parts that looked like they might be useful but would not be needed if I was skillful and lucky. A very senior engineer was hired into our company to oversee and guide us newer ones. One day he came by my workbench, looked at the schematic of a video circuit I was developing and asked "Why did you leave out the base stop resistors?" (Base stop resistors lower the Q of the circuit to which a high frequency is connected and reduces the chance of the stage oscillating.)

His name was Don Klein. Don said "Our main job is to keep out of manufacturing. You never know when those parts will be needed, so always use them." He was right. A lot of those "extra parts" were there to compensate for variations in components and make circuit performance more consistent as opposed to sometimes being on the hairy edge of not working.

Bypass capacitors are sometimes left out of circuits because the need for them was not obvious. Sometimes it is ok, and sometimes it isn't.
 

Arjune

Joined Jan 6, 2018
196
The standard way of learning will not help a person break free from the trap of working life. Sulvek, the subconscious is questioning the conscious for a reason why we do and why we do not do. Force is not asking the mind for a reason to exert itself, so the mind is annoyed. I'm wondering since plates are so close to one another in a capacitor, how are they (manufacturers) able to keep the dielectric thin without the plates getting shorted. I always thought you could use polyester capacitors, mica capacitors, maylar or ceramic capacitors interchangeably and I really don't know the reason why a specific one will be used in a circuit. I can now extrapolate that the unknown non-existent intelligence wants to know why the associated force should exert itself without permission from what is in effect nothing. It appears that the theory was created without permission from the subconscious.
 

WBahn

Joined Mar 31, 2012
27,392
The standard way of learning will not help a person break free from the trap of working life. Sulvek, the subconscious is questioning the conscious for a reason why we do and why we do not do. Force is not asking the mind for a reason to exert itself, so the mind is annoyed. I'm wondering since plates are so close to one another in a capacitor, how are they (manufacturers) able to keep the dielectric thin without the plates getting shorted. I always thought you could use polyester capacitors, mica capacitors, maylar or ceramic capacitors interchangeably and I really don't know the reason why a specific one will be used in a circuit. I can now extrapolate that the unknown non-existent intelligence wants to know why the associated force should exert itself without permission from what is in effect nothing. It appears that the theory was created without permission from the subconscious.
Pulling out the little bit of coherent content embedded in the middle of... whatever: "I'm wondering since plates are so close to one another in a capacitor, how are they (manufacturers) able to keep the dielectric thin without the plates getting shorted. I always thought you could use polyester capacitors, mica capacitors, maylar or ceramic capacitors interchangeably and I really don't know the reason why a specific one will be used in a circuit."

Manufacturing processes vary widely for different types of capacitors. In the case of something like aluminum electrolytic capacitors, the dielectric that separates the plates is actually a film created by a chemical reaction on the plate itself, thus it is incredibly thin, which is why these capacitors can have such high capacitances for their size compared to most other types.

As for the why you use one over another for specific purposes in a circuit, the reason is that a capacitor (like just about every type of component) has many different characteristics besides just its capacitance. These include things like tolerance, physical size, voltage limitation, peak current capability, leakage current, parasitic inductance, effective series resistance, temperature coefficient, long-term stability, voltage coefficient, and more. In one application a couple of these might be absolutely critical while in another application the designer could care less about them.
 
Top