A diode is a component that lets current flow in one direction and blocks it from flowing in the other direction. It has two pins; anode and cathode.
The diode symbol looks like an arrow pointing toward a line. The line represents the cathode side, and so does the line marking on the diode component itself.
How To Connect A Diode in a Circuit?
A diode will block or let current flow, depending on how you connect it in a circuit. Below you can see an example circuit.
In the circuit above the diode is connected in the right direction. This means current can flow through it so that the Light-emitting diode (LED) will light up.
But what happens if we connect it the other way around?
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?
A standard diode can be used for a range of things, from creating sound effects to power supplies. Below, you can see a few circuit examples with an explanation of what the diode is used for:
Sound Effects Clipping: By placing two diodes in parallel in opposite directions, you can get a clipping effect which creates an overdrive sound effect, often used in guitar pedals.
Converting from AC to DC: Sometimes diodes are used to convert from AC to DC by placing four rectifier diodes to create a bridge rectifier. This is often used after a transformer in a power supply, followed by a voltage regulator.
Protecting from voltage spikes: Components like motors and relays are basically inductors, which means their current will try to keep on flowing after the power is shut off. Diodes are used to safely discharge them.
How a Diode Works
The diode is created from a PN junction. You get a PN junction by taking a negatively doped and positively doped semiconductor material and putting it together.
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.
How To Test Diodes With a Multimeter
You can test diodes with a multimeter to find the forward voltage. To test your diode, you need a multimeter with a diode function. If you see a diode symbol on your multimeter, that’s most likely your diode function.
- Connect the positive test lead to the diode’s anode.
- Connect the negative test lead to the diode’s cathode.
- The multimeter display will show you the forward voltage of your diode.
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 0.7 V to 1 V.
- It has 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 diode
- Rectifier diode
- Zener diode
- Light-Emitting Diodes (LED)
- Schottky Diode
- Photodiode
- PIN diode
Signal and rectifier diodes are pretty much the same things 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.
Schottky Diodes have a lower forward voltage drop and faster switching speeds than standard signal diodes.
Photodiodes are diodes that are sensitive to light. They let current flow through them when exposed to light.
Light-Emitting Diodes (LED) are components that light up when current flows through them.
Questions
Do you have any questions about diodes or any feedback you want to share? Let me know in the comment field below!
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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 ?
Yes, many of the standard wall adapters are transformer-less these days.
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.
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
Thanks or the eye opener…
awesome!
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. .
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!!!
Nobody had ever explained a diode in such simpler words!👍
regarding to Zener diode,what do you mean by saying it acts as a very stable voltage references?
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.
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.
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?
Probably yes, but I’m guessing here as I haven’t tested this with lots of diodes.