Capacitors

Other Hardware General Electronics
1

Actually, what is the use of capacitors?

2

Hi,
Most simply:

  • Capacitors (called 'condensers' when I was first an Engineer) oppose the change of VOLTAGE in a circuit.
  • So they are good at "smoothing" varying voltages. Ie. "Filter Capacitors".
  • They also are good for "coupling" changes in voltage (like Signals) while not passing unchanging (DC) voltages. Ie. "Coupling Capacitors".

BTW:

-Inductors are the opposite: They opposed the change of CURRENT in a circuit...

3

Capacitating

4

They are essential for supply decoupling, without which nothing much would work:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Along with an inductor a capacitor makes a resonant circuit, without which there would be no radio or TV transmitters.

5

terryking228:
Hi,
Most simply:

  • Capacitors (called 'condensers' when I was first an Engineer) oppose the change of VOLTAGE in a circuit.
  • So they are good at "smoothing" varying voltages. Ie. "Filter Capacitors".
  • They also are good for "coupling" changes in voltage (like Signals) while not passing unchanging (DC) voltages. Ie. "Coupling Capacitors".

BTW:

-Inductors are the opposite: They opposed the change of CURRENT in a circuit...

So when would you really use a Inductor for Smoothing? Like in Power Supplies or something?

6

So when would you really use a Inductor

In decoupling (as my previous link) for resonant circuits (including oscillators), for filters, for antenna (RFID).

7

For use in power supplies, in simple terms, think of a capacitor as a "cylinder" rather like a water cylinder which has the ability to collect and store (noisy) input voltage and give out (smoother) voltage. For voltage smoothing the capacitor is fitted across (in parallel with) the supply line.

an inductor can be considered as a "resistor" that blocks noisy current without the corresponding waste of power (creation of heat) that a resistor would produce. It is normally fitted in series with the power supply line, immediately before the corresponding smoothing capacitor. Note that a resistor is often used as, but much less effective, alternative to an inductor.

8

So when would you really use a Inductor?
(Grumpy Mike)
In decoupling (as my previous link) for resonant circuits (including oscillators), for filters, for antenna (RFID).

It sounds like you can use either a capacitor (in parallel) or an inductor (in series) for removing unwanted noise.
When do you use one and when the other?

There are many different types of capacitor. I have a circuit which uses electrolytics; mainly on regulators.
I am concerned about the finite life span of electrolytics, especially in warm enclosures.

Can I use any type of capacitor (with a longer lifespan) of the same value as a replacement for the electrolytics or do they have some unique property that makes them 'un-substitutable'?

9

Can I use any type of capacitor (with a longer lifespan) of the same value as a replacement for the electrolytics

In theory yes, but practically no, because large values of capacitors are only available in electrolytics. So while you can easily get a 0.1uF ceramic getting 100uF would require 1000 of them in parallel.

I am concerned about the finite life span of electrolytics

There are lots of different grades of electrolytic capacitor, some have longer life that others.

especially in warm enclosures

Approximately for every 10C less you run them their life time doubles. Note that the life time is quoted as the time it takes for the capacitance to halve.

It sounds like you can use either a capacitor (in parallel) or an inductor (in series) for removing unwanted noise.

They are not quite interchangeable, you would use a capacitor first because that gives a lower impedance solution which is what you want from a power supply. Then for added reduction use the inductor as well as the capacitor. You would never use an inductor on it's own for removing noise because it is not so effective and produces a high impedance supply.