What is capacitor? Principle working, types and how it works

I believe that you used capacitors in electronic circuits. Do you understand the principles and usage of it? Let me explain to you to learn more. You may apply them. To develop electronic projects Or can solve your job.

It has the following unique characteristics.

  • Store the electrical current.
  • Block DC current not passing it
  • Allow AC current to flow through it.

Are you ready?

What is a capacitor?

A capacitor is a basic electronic device to store electrical charges. You may not see enough images.

Recommended: Basic capacitor principle in short

Look at the image. Have you ever watched an Ancient war movie?

Imagine we might be able to compare a capacitor with a normal spring.

Comparing of capacitor operation with normal spring

In first, a spring collapses. Then, we stretch or pull the spring out. It means we are giving energy to the spring.

It stores energy from us!

After that, we released it. The spring will collapse back to its original state. It causes the stone to be ejected.

So what?

Basic Capacitor Structure

Look at the basic structure of the capacitor below.

basic structure of capacitor

It consists of 2 conductors. It is called the “Plates”. And separated by “Dielectric”.

Which is made by electrical insulation such as paper, mica, ceramics, or air, etc.

See in the image again, this is a fixed capacitor.

We often call the type of capacitor according to the substances used to make the dielectric.

For example, ceramic capacitors also there will be a dielectric that is ceramic.

Factors affecting capacitance

The variant that makes the value of the capacitor more or less, have 3 things as follows.

Factors affecting capacitance
  • Case 1# The area of the plates parallel to each other. The capacitor has an area of plates very much. So it is the greater the capacitance.
  • Case 2# If the distance between the plates is greater, it will reduce the capacitance.
  • Case 3# Change the dielectric substance. It causes the capacitance to change, as well.

Specifying and value of Capacitor

The value of the capacitor, we called capacitance. It is the ability to store electrons.

The capacitor unit is Farad. We can write the abbreviation: F.

A 1-farad capacitor connect to A 1-volt supply will store 6,280,000,000,000,000,000(6.28×10-18) electrons!

So in practice, 1 farad is very valuable. Most capacitors have much smaller values.

We often see most capacitors:

  • Microfarads (Millionths of a farad) is Large specified capacitors.
  • Picofarads (Trillionths of a farad) is Smaller specified capacitors.


  • 1- Farad = 1F
  • 1-Microfarad = 1μF = 0.000001F = 1/1,000,000F
  • 1-Picofarad = 1pF = 0.000 000 000 001F = 1/1,000,000,000,000F
  • 1-Picofarad = 0.000001μF = 1/1,000,000 μF

Microfarad = Picofarad/1,000,000

Farad (F)Microfarad (μF)Picofarad (pF)
0.001 1,000 μF1,000,000,000 pF
0.0001 100 μF100,000,000 pF
0.00001 10 μF10,000,000 pF
0.000001 1 μF1,000,000 pF
0.0000001 0.1 μF100,000 pF
0.00000001 0.01 μF10,000 pF
0.000000001 0.001 μF1,000 pF

Capacitor Working principle

As above, we know the capacitor runs with charge and discharge. But some may not clearly understanding.

I hope you get 2 ideas below.

Charging A capacitor

It is to store the electron at a plate of the capacitor. Which we explained in detail in the diagram below (B).

When connecting a battery to the capacitor. The electrons from the negative of the battery will gather at the plate.

It causes negative ions. And, Also sends an electric field to push the electron of the opposite plate.

As if bringing magnets with the same polarity near each other, they would push together.

Usually in the plates are + and – ions mixed together. When the electrons from this plate are pushed out.

Leaving a positive ion greater than negative ion.

The more electrons are pushed away, the plate will only be more positive. (Compared to the other side)

Note: If my text is not clear please see in the diagram better.

If we want to observe the operation of the capacitor more clearly. We have a simple method is using limiting current resistors in series.

Look at the circuit diagram below.

Resistor help capacitor charging learning

You can slow down the charging time. By placing a resistor between the capacitor and a 9V battery.

And you can see a graph of the charging time easily.

In first, peak current flows capacitor and slow down to zero. In a delay time with Resistor and Capacitor value.

Discharging A capacitor

The capacitor has been charged. If we have not yet connected the terminals of the capacitor together. The electrons are still on the plate.

Then, it will gradually leak through the dielectric until both plates have an equal charge.

But if there is a short circuit or complete circuit between the plates. As Figure below.

The electrons will run a complete circuit from the negative plate to the positive plate immediately. We call this event “Discharging”

What is more?

As above we add the resistor. The capacitor will discharge more slowly. And See the graph the discharge time.

The voltage of the capacitor will gradually reduce to OV.

Learn: Relationship Between Current and Voltage

Type of capacitors

We often see the two most common capacitors: fixed value capacitors and variable capacitors. These are discussed below.

Fixed Capacitors

The fixed capacitors used today are of many types. We label them according to their dielectric.

For example, ceramic, mica, mylar, polystyrene, polyester, paper, electrolytic, tantalum, and many others.

But for I like to use only 3 types which are Electrolytic, Ceramic, and Mylar. Because they are suitable for general work And inexpensive as well.

3 most common capacitor types

And here are just two types of examples, Electrolytic and Ceramic types only.

The Ceramic Capacitors

Shape of Ceramic Capacitors

In general, it looks like round, flat, orange. As the figure shows.

Most of them are less than 1 µF.

And it will be a non-polar type capacitor. (When using, there is no need to consider the polarity at all.)

And, it can withstand a voltage of about 50V – 100V.

The capacity of the Ceramic Capacitor that we currently use is from 1pF to 1µF.

Electrolytic Capacitors

This type of capacitor must be careful when using it. Because there is a very specific polarity.

It will be printed to clearly indicate the side of the body.

Electrolytic Capacitors shape

Do not wrong Polarity

If entering a voltage for a capacitor in the wrong polarity. It will get damage immediately.

The terminals of this type of capacitor can be easily observed.

When buying from a store, long legs are positive and short legs are negative.

Cautions Working voltage of Capacitor

The First caution: All capacitor has a voltage rating. Or we called a working voltage (WV).

We must supply a voltage to the capacitor that is lower than this rate.

If you neglect or ignore this requirement. I have missed this.

I do not want to see you sad like me. The too high voltage can kill it.

In general use, we will reserve the voltage of the capacitor about 2 times of the actual operating voltage.

For example, the ceramic capacitor will have a voltage rating of 50 volts (V). We must use an input voltage is of about 25V or lower.

Substitution capacitor

Have you ever read the techniques for buying electronic devices worthwhile?

We should always choose the one with a working voltage higher first.

For example:

Between 50V and 100V values. We should choose 100V. Because it can be used to replace 50V.

Warning High voltage in a capacitor

Oops! something went wrong.

It sparks at the tip of the test probe. While I was measuring a resistor on a power supply PCB.

What happened?

In large electrolytic capacitor may charge a voltage of 100 to 200 volts.

When the tip of metal touches both leads. The highest current is short circuit in fast. It can melt anything.

Sure It is too dangerous. Image if your finger? touch it. It can kill you too.

For safety reasons, I will always discharge it. When working with it.

A lamp as load

The simple method is to use a light bulb to connect each of the electrolytic capacitors.

Variable capacitors

They often have non-moving plates and moving plates. The capacitance is changed by rotating a rod affixed to one side of the movable places.

We can adjust the capacitances by turning the axis of the capacitor.

When we rotate a rod affixed the movable places. The capacitances will change with our rotating.

We can divide them into 2 types

Trimmer capacitors

Look at the diagram below.

Trimmer capacitors working

This type is used to tune the oscillator. I often see in FM wireless transmitter or digital watches. They are small.

Variable capacitor

We use this type to tune radio receivers and transmitters. The dielectric is usually Air. Look diagram below.

How to Read code capacitor

Since most Ceramic and Mylar capacitors are small. Manufacturers have to label the code instead of the capacitance.

Below is a way to decode a capacitor. It may be difficult at the start time.

But when you look at the example Probably understand its technique.

  • First and Second Digit are fixed numbers having units in pF.
  • The third is Multiplier with number ten raised to the power. For example 10³.
  • Fourth is tolerance level such as J = 5%, K = 10%, M = 20%.

How to do?

Nonpolarized capacitor code
  • What is the 101K capacitor Value?
    First Digit = 1
    Second Digit = 0
    Multiplier = 101, or It means : 0pF (Zero PicoFarad)
    Tolerance K = 10%
    101K = 100pF = 0.0001μF and 10% tolerance.

    What is more?
  • 473K capacitor value?
    First Digit = 4
    Second Digit = 7
    Multiplier = 103, or It means : 000pF (Three PicoFarad)
    Tolerance K = 10%
    473K = 47 000pF = 0.047μF and 10% tolerance
  • 102M : 10 x 102 pF = 10 00pF. Which it is 0.001μF and 20% tolerance.
  • 103J : 10 x 103 pF = 10 000pF. Which it is 0.01μF and 5% tolerance.
  • 104J : 10 x 104 pF = 10 0000pF. Which it is 0.1μF and 5% tolerance.

    Do you understand?

Application Capacitors

We use the capacitors in many electronic circuits. They are important components. Here are some why we use them.

Power supply Filter

Power supply filter

We always use the capacitors in the power supply filter. They will smooth the pulsating voltage into a steady direct current (DC).

Related: Learn Filter Capacitor in supply circuit

The digital Spike remover

Why my digital circuit runs error? It is not stable.

Let’s try this tip. Add the 0.1uF capacitor across the power supply terminals. As the circuit diagram below.

Digital Spike remover for digital using a capacitor

But it has a huge impact. For nearby circuits. Look at the signal in the image graph.

Compare the voltage levels when adding the capacitor

Compare the voltage levels when adding the capacitor.

  • A: The voltage level without a capacitor.
  • B: The voltage level with the capacitor.

Capacitor Switch transients protection

While turning on and off the electrical switch in the house. Have you ever heard a brief disturbance?

How did it happen?

It is caused by the contacts of the switches touching each other. It is a spike voltage.

Even for a short time But the electric current is very high. Which is higher than normal.

So, able to disturb nearby electronic circuits.

How can we reduce this problem?

As we know the working principle of the capacitor. It likes high frequency. We then put it across the switch.

Look at the circuit diagram.

I use 0.1uF 630V Mylar or Ceramic capacitor.

It will absorb the transients or spike voltage well. You will notice that the noise disappeared.


The capacitors are basic components. But they are very helpful for all the electronics. Can you use them?

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