If you have embarked upon electronics projects in the past, there is a good chance you have already encountered this common component and soldered into your circuit without second thought. Diodes are valuable in electronics and serve a variety of purposes, which will be highlighted in upcoming steps.

First, what is a diode?

A diode is a semiconducting device,  that allows current to flow in one direction but not the other.  

A semiconductor is a kind of material, in this case silicon or germanium, whose electrical properties lie between those of conductors (metals) and insulators (glass, rubber). Consider conduction: its is a measure of the relative ease of which electrons move through a material. For example, electrons move easily through a piece of metal wire. You can change the behavior of a pure material, like silicon, and turn it into a semiconductor by doping. In doping, you mix a small amount of an impurity into the pure crystalline structure.

The kinds of impurities added to pure silicon can be classified as N-type or P-type.
  • N-type:  With N-type doping, phosphorus or arsenic is added, in parts per billion, to the silicon in small quantities. Phosphorus and arsenic both have five outer electrons, so they are displaced when they get into the silicon lattice. The fifth electron has nothing to bond to, so it's free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. Electrons have a negative charge, hence the name N-type.
  • P-type - In P-type doping, boron or gallium is  added to the pure silicon. Those elements each have three outer electrons. When mixed into the silicon structure, they form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbor, moving the hole over a space. 

Diodes are made from two differently doped layers of semiconductor material that form a PN junction. The P-type material has a surplus of positive charge carriers (holes) and the N type, a surplus of electrons. Between these layers, where the P-type and N-type materials meet, holes and electrons combine, with excees electrons combining with excess holes to cancel each other out, so a thin layer is created that has neither positive nor negative charge carriers present. This is called the depletion layer.

There are no charge carriers in this depletion layer and no current can flow across it.  But when a voltage is applied across the junction however, so that the P-type anode is made positive and the N-type cathode negative, the positive holes are attracted across the depletion layer towards the negative cathode, also the negative electrons are attracted towards the positive anode and current flows.

Think of a diode as a one-way street for electricity. When the diode is in forward bias, the diode allows traffic, or current, to flow from the anode, towards the cathode leg. In a reverse bias current is blocked so there is no flow of electricity through the circuit. When current is flowing through a diode, the voltage on the positive leg is higher than on the negative leg, this is called the diode's forward voltage drop. The severity of the voltage drop is a function of  the semiconductor material that the diode is made from. When the voltage across the diode is positive, a lot of current can flow once the voltage becomes large enough. When the voltage across the diode is negative, virtually no current flows.

Step 1: Different uses for different Diodes.

There are many different kinds of diodes, and each one serves a different purpose as an electronic component.

A Light Emitting Diode or LED is probably the most well known and most easily identified. The LED emits visible light when electrons jump across the PN junction.The resulting light is referred to as electroluminescence.

Photodiodes conduct only when they are exposed to light. These can be useful in making projects with a light activated switch, so that a circuit in only active in the presence of light.

Zenerdiodes are designed to conduct in the reverse direction, only when something called the breakdown voltage is reached will the circuit conduct. These are dialed to precise tolerances, see the section on Zener Diodes in step 3.

Rectifier diodes are designed to stop electricity from flowing in the wrong direction. Diodes are sometimes known as rectifiers for their use to rectify alternating current electricity into direct current, by removing the negative portion of the current.

Schottkydiodes are designed to turn on and off very rapidly when the breakdown voltage is reached, responding quickly in digital circuits. When current flows through a diode there is a very small voltage drop across the terminals.  Silicon diodes have a voltage drop, or loss; a Schottky diode voltage drop is significantly less. This lower voltage drop enables higher switching speed and better system efficiency.

Diodes can be used in a number of ways, like to protect a current-sensitive circuit. A device that uses batteries will likely contain a diode that protects it when battery is inserted improperly. The diode will stop the reversed current from traveling from the battery to the rest of the circuit-- thus, the diode protects the sensitive electronics inside the your circuit.

In the next few steps, you will find information about some of the most commonly used kinds of diodes.
<p>i have a set of leds that im tring to power from 2 different sourses. 1st sources is a automobile dome light and the 2nd is a head light switch. what kind of diode can i install on each source. i want the LED lights to turn on when the head lights or the dome light are on without cross powering the other source. (ex, so when the head lights are on, it wont power the dome light.)</p>
<p>if i have a 5v solar panel, which i use to charge my mobile phone. Do i need to put any kind of diode to stop the current flow back to solar cell from mobile battery..?? plz let me know if i need to use any.</p>
<p>no solar panel itself is not consumer (if you put diode voltage will fall to 4.8-4.92)</p>
thank you
<p>No, you can thank the usb standard and battery protection circuitry. As long as it's an unmodified usb cable, you are fine. You can add a diode if you want, but I'm sure there already in there. </p>
<p>This would be very helpful, my science fair project is testing the efficiency of renewable energy sources.</p>
<p>any idea which diode i should use ?</p>
<p>Take a look at this guide. The voltage is a little smaller, but the princible should still be the samehttp://www.instructables.com/id/Solar-Altoids-USB-Charger/</p>
<p>Your phone probably has some kind of protection so that won't happen,</p><p>BUT, if it doesn't, you cant add a diode because it will lower the voltage to 4.3 volts, or 4.6 volts if you use a schottky diode</p>
I want to use a 45 watt solar panel from HarborFreight to charge a 36 volt Golf Cart. Any Ideas on the type of diode I need?
<p>did you found which diode to use?)))</p>
I have a 9v dc motor I tried to charge a battery with it but the electriccity return to the motor what type of diode i have to use please tell with photos
<p>Schottky or rectification diode for ex 1N4007</p>
<p>Hey, I am Siray. I need to know how the diode blocks the current flowing in an incorrect way. I mean it acts like a resistor or it only block it by reversing it in the other direction or what exactly.</p>
<p>read how semiconductors acts</p>
<p>I must say this sight is a learning center an props to those who keep it runing</p>
<p>Wow! The best overview + explanation + application guide for diodes I've found on the web. Wonderfully informative &amp; just technical enough, for me, to get my layman's mind wrapped around the concepts without making my head hurt. Thank-you audreyobscura &amp; well done :)</p>
<p>hi, im working with secuencers / synths, one question, shall i use a diode for every output/input (for example a clock out), im using a 4514 and im wondering if i shall use a diode for every output, maybe someone puts a clock signal to an output, i dont know if that might ruin the chip</p><p>thanks!</p>
<p>Great job</p>
Please tell me there is more to come!.....It would be neat to have a refresher for all basic components.<br><br>Dan
<p>I really agree!!!! pleaseeeeee do it :)</p>
<p>If I took the number of diodes in the matrix example and put them in series, will I just need one resister and how will the power draw and illumination change of the individual LEDs change?</p>
<p>My instructor just published an article on how to test <br>diodes with both an analog and digital multimeter and goes in a little more <br>detail regarding why the meter might read infinity. <a href="http://www.ciebookstore.com/how-to-check-diodes-with-a-multimeter" rel="nofollow">http://www.ciebookstore.com/how-to-check-diodes-wi...</a></p><p>But this is a great overview of diodes. Thanks!</p><p></p>
<p>Nice information. An analogy I use for diodes is to think the body of it as a hallway with a door (the line) that opens outward allowing bodies (voltage) to pass through. With a large enough body pushing on the other side, it could be made to swing inward and too much weight (current) will permanently break it down.</p>
Nice clear explanations, really helpful!
Regarding Schottky diodes defined as having high switching speed. On a project I was building, the schematic called for a diode type 1N914. I first assumed that by staying within the expected circuit voltage and current characteristics in that part of the circuit, any diode will do. However the project did not work and I consulted a manufacturer's leaflet for 1N914. The diode I needed was described as &quot;Silicon rectifier diode/Ultra fast switch&quot; . Since this description as well as the symbol used on the schematic were unrelated to a Schottky device one should conclude that there are other devices besides the Schottky diode that will provide high switching speeds. Is that a wrong statement? In fact the litterature I consulted used the technical wording &quot;reverse recovery time&quot; (4 nanoseconds for a reverse voltage of 6V)... and my circuit started working.
You need a current limiting resistor in series with most LEDs, although some have this resistor built-in. Without a current limiting series resistor, excess current can be drawn when forward biased and 'burn out' the LED. Different voltage sources will require different resistor values. Use ohm's law E=IR, allowing say a 3 volt drop across the LED, and limit the current to perhaps 20 milliamperes and experiment from there.<br><br>The LED here probably has a built-in resistor designed for 5 volt operation.
How do you know how much current or voltage that you can safely put to a LED without harming it, yet get the most light and life from it? Is a 3 volt drop and a 20 mA current a standard for all or is there a tech sheet included with LED's explaining what they will and won't take? <br> I want to know so if I decide to wire some up to a 12 or 24 volt system, I'll have an idea as to how many I should (or can) put in series and what size and wattage resistor I should use. <br>Can you help?
The approx 3 volt &quot;drop&quot; across the LED depends on its colour - red being minimum and blue being maximum. The current allowable really is determined by the power dissipation capability of the LED, and can be found on the specification sheet for any particular type of LED. 20 ma and 3 volts will keep you in a safe region for most LEDs. You could experiment with one LED and measure its voltage drop, and run it at various currents to see how hot it gets, or at what current it is destroyed.<br><br>Sorry I can't really be more specific. You can get an apparent brighter LED by pulsing it at say 50 Hz or higher, and keeping the duty cycle down but while lit, driving it at many times its current, keeping the average heat down.<br><br>Hope this helps.<br><br>de Bob VE3SUY<br><br>
You make it sound as if schottky diodes are better in every way. Do they have any drawbacks? (if they do, this content should probably be added)
Schottky diodes are not high voltage diodes.
In Science and experiments, description and procedures may contain simple errors and omissions. That is not to be considered as a draw back. Please respect the scientist and try to contribute like him, instead of commenting. <br>Thank you, AuderyObscura, your contribution is great and I am thankful to you. <br>We look forward to reading more from you.
Nice, but I need to be a bit picky just to make it a bit better: <br> <br>1) if any of the leds are reversed it will not light nor will the led in series with it ( unless you break down the reversed led as with a zeener ) <br> <br>2 the graphic has 1 ohm printed should be 1k ohm as the text says, also color code looks a bit like 10k, but I may be wrong on that one. <br> <br>
Thanks for the tip - I went through and made the diagram a bit more clear.
Great instructable! I would like to make a night vision using invisible LED's and an IR detector. I would also want to have the ability to run the lights full time for my camera, that can see in the dark with these diodes. I want to put it on the dash to see better at night, like deer, SKUNKS, and other wildlife... I want to be able to see someone jacking up a car when there are headlights behind him blinding me. The IR will let me see everything within range. I have 17 invisible LED's, an old VHS camera with zoom ability. <br> <br>Right now, I don't have time to put such a device together. I still have to buy a battery and charger at Batteries Plus here in the local area of KCMO. <br>I went through engineering school, but I just don't have the time. I am working on an all electric car that will beat all production cars. I am only building one. I just got the electric motor to run my high powered hydrostatic drive system. This car is so advanced compared to most vehicles, but now GM and others are catching up with parts like magnetic suspension. I am also using a magnetic clutch that acts like a full time regenerative system. There is so much more to this project. I can't go into details right now, I am sure some special interest groups won't let me divulge either.
Just a quick reminder to ALWAYS use a resistor when wiring up LED's to a power source - the circuit resistance of the diode is so low that directly attached to a power source, it acts as a dead short circuit!<br><br>I have ruined several adjustable 12 volt car power adapters after miscalculating the resistance of several LED's in series for a lighting project.<br><br>Remember from then that you may have to recalculate your power needs, especially if you have either a very low current power supply - or a lot of LED's on a higher power supply!<br><br>In any project, always have a multimeter to hand to check your values and do not hesistate to have Ohm's law written down somewhere so you can check that you are calculating values the right way! <br><br>Cheers,<br>Daniel
At LOW voltages, using schottky barriers may save a lot of power, but if you have a 12V supply, running at 1A, the diode drop is losing you .6W, or 0.3W if you go Schottky. 5%, to 2.5%. At lower currents, or higher voltage, it often doesn't matter. <br><br>
A ZENER is a voltage reference device, not used as a &quot;switch&quot; !
Thanks for the informative How-to. <br>I have a small solar panel that I want to charge a battery with. I was given a diode to keep the battery from discharging. <br>Can you tell me by the marking on the diode which direction is the permited flow and which direction the flow is stopped? <br>Thanks.
It should have a band around one end. I am 90% sure that the end with the band goes to the negative terminal to forward bias.
thanks for the education, I'd wondered on the science behind how a diode worked.<br>
In the picture in Step 1, generic is misspelled.<br>Otherwise, great 'ible! Very clear.
Also, typo in the first picture in Step 4, there are 3 r's in current.
hey thanks! one day i'll get it! I made the corrections to both. :)
Thanks for the well-written descriptive yet simple guide to diodes!
Sweet! Ive always wanted to learn how to diode!

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