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You are here: Home / Basic Electronics / What is a Diode?

What is a Diode?

September 10, 2013 By Øyvind Nydal Dahl 16 Comments

I’ve been asked a few times – what is a diode?

Diode IR 10D 9F

Well, a diode is an electronic component that conducts current in one direction and blocks current from flowing in the other direction.

The diode symbol looks like this:
Diode symbol

How To Connect A Diode

Let’s look at an example.

How diodes work - right direction

In the circuit above the diode is connected in the right direction. This means current can flow through it so that the LED will light up.

But what happens if we connect it the other way around?

How diodes work - wrong direction

In this second circuit the diode is connected the wrong way. This means that no current will flow in the circuit and the LED will be turned OFF.

What Is a Diode Used For?

Diodes are very often used in power supplies. From the power outlet in your wall you get alternating current (AC). A lot of the devices we use need direct current (DC). To get DC from AC we need a rectifier circuit. It’s a circuit that converts from alternating current (AC) to direct current (DC). Diodes are the main components in rectifier circuits.

How a Diode Works

The diode is created from a PN junction. You get a PN junction by taking negative doped and positive doped semiconductor material and putting it together.

What is a diode? Diode PN Junction, symbol and look of component

At the intersection of these two materials a “depletion region” appears. This depletion region acts as an insulator and refuses to let any current pass.

When you apply a positive voltage from the positive side to the negative side, the “depletion layer” between the two materials disappears and the current can flow from the positive to the negative side.

When you apply a voltage in the other direction, from the negative to the positive side, the depletion region expands and resists any current flowing.

Things To Note About Diodes

  • You have to apply enough voltage in the “right” direction – from positive to negative – for the diode to start conducting. Usually this voltage is around 0.7V.
  • The diode have limits and cannot conduct unlimited amounts of current.
  • Diodes are not perfect components. If you apply voltage in the wrong direction, there will be a little bit of current flowing. This current is called “leakage current”.
  • If you apply a high enough voltage in the “wrong” direction, the diode will break down and let current pass in this direction too.

Types of Diodes

There are many different types of diodes. The most common ones are signal diodes, rectifier diodes, zener diodes and Light-Emitting Diodes (LED). Signal and rectifier diodes are pretty much the same thing except that rectifier diodes are built to handle more power.

Zener diodes are diodes that make use of the breakdown voltage when applying voltage the “wrong” way. They act as very stable voltage references.

Share your comments or questions below!

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Filed Under: Basic Electronics

Reader Interactions

Comments


  1. Dan Okrasinski (a.k.a. DanO) says

    September 28, 2013

    Have I signed up for your newsletter. If not email:
    [email protected]
    Also have they made any transformer less voltage reducers for a hobby user. Say 120 AC to 12 AC volts. Are “wall warts” transformerless or do they have small gauge wire windings inside ?

    Reply

    • admin says

      October 3, 2013

      Yes, many of the standard wall adapters are transformer-less these days.

      Reply

  2. suraj says

    May 27, 2014

    thanks

    Reply

  3. Ken Murray says

    November 14, 2014

    Hi, Thanks for this quick section on diodes. I understand why one would use this in a power supply since AC goes back and forth and you only want one direction in DC. Could you pass on some more info on why they would be used or which other situations you would need this in a circuit? Thanks again or the help.

    Reply

    • admin says

      November 16, 2014

      Hi Ken,

      Good question. First of all, I would recommend to not get too hung up on the diode as you are starting out. You don’t need it that often. Except for the Light-Emitting Diode (https://www.build-electronic-circuits.com/what-is-an-led/)

      But you can use it to protect your circuit from damage if someone connects the battery in the wrong way (minus on plus, and vice versa).

      And another very common use is the fly-back diode. It’s a way to protect your circuit from voltage spikes created by motors or relays.

      There are a lot of special cases and a lot of different types of diodes: https://www.build-electronic-circuits.com/types-of-diodes

      Cheers!
      Oyvind

      Reply

  4. Olecks says

    November 14, 2014

    Thanks or the eye opener…

    Reply

  5. Lawrence says

    February 17, 2015

    awesome!

    Reply

  6. Hasan Yahya says

    September 3, 2015

    Thank to author who had presented a valuable article. I have a suggestion : the figure should be equipped with the plug and socket for easier understanding how a diode work. .

    Reply

  7. Marcus Bralic says

    April 4, 2017

    Great artical, very insightful! Thanks for making this great website! I was intimidated by electronics but this site has Given me the confidence to pursue my new hobby!! You rock!!!

    Reply

  8. Subhash says

    June 23, 2017

    Nobody had ever explained a diode in such simpler words!👍

    Reply

  9. Chizoo says

    October 3, 2017

    regarding to Zener diode,what do you mean by saying it acts as a very stable voltage references?

    Reply

    • admin says

      October 6, 2017

      For example a 4.7V zener diode will have a 4.7V drop in the reverse direction. This you can use for a stable 4.7V reference to for example a analog to digital converter.

      It won’t let you source a lot of current though.

      Reply

  10. monkman says

    March 22, 2018

    thanks

    Reply

  11. Alex says

    May 6, 2018

    I never done any circuits, but I need to drop from 5 to 4 volts without any ICs, because they cost money. So I take two diodes sequental to drop around 0.5v on each (from a bridge) and add 5w 47ohm resistor to drop current (I use ATX PSU) and a 3300uF 10v capacitor as a filter and stabilizer, and before all that someone recommends to add an inductor to build more complete filter.

    I have also three shottka packs, two for 40A and one for 15A, but I think it is not possible to use them for that “dc-dc converter”.

    Btw I need 4.2v and 2-3 A of current, which make me sad.
    Yes it is broken tablet that can only run from cable soldered to battery contacts.

    Reply

  12. Sheikh Miraz Mirza says

    November 20, 2020

    You said, in the diode if high voltage is provided in the wrong direction, the diode can break down and let current flow through that wrong direction too.
    In that case, shall we see any visible destruction sign or black ash on or around that diode?

    Reply

    • admin says

      November 23, 2020

      Probably yes, but I’m guessing here as I haven’t tested this with lots of diodes.

      Reply

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