The phosphorus atom has 5 electrons in its valence shell. With P-type doping we add in a material such as aluminium,. There is therefore a hole created where an electron can sit and occupy.
So we now have two doped pieces of silicon, one with too many electrons and one with not enough electrons. The two materials join to form a P-N junction. In this region, some of the excess electrons from the N-type side will move over to occupy the holes in the P-type side.
This migration will form a barrier with a buildup of electrons and holes on the opposite sides. The electrons are negatively charged and the holes are considered therefore positively charged.
So the build up causes a slightly negatively charged region and a slightly positively charged region. This creates an electric field and prevents more electrons from moving across. The potential difference across this region is about 0.
When we connect a voltage source across the diode, with the anode P-Type connected to the positive and the cathode N connected to the negative, this will create a forward bias and allow current to flow. The voltage source has to be greater than the 0. When we reverse the power supply so the positive is connected to the N-type cathode and the negative is connected to the P-type anode. The holes are pulled towards the negative and the electrons are pulled towards the positive which causes the barrier to expand, and therefore the diode acts as a conductor to prevent the flow of current.
Diodes are represented in engineering drawings with a symbol like the image above. The stripe on the body is indicated with a vertical line on the symbol and the arrow points in the direction of conventional current. When we look at a diode we see these numbers and letters on the body. These identify the diode so you can find the technical details online. The diode will have an I-V diagram that looks like above.
This diagram plots the current and voltage characteristics of a diode which is plotted to form a curved line. This side is how it should perform when acting as a conductor and this side is when acting as an insulator. You can see that the diode can only act as an insulator up to a certain voltage difference across it, if you exceed this, then it will become a conductor and allow current to flow.
This will destroy the diode and probably your circuit, so you need to make sure the diode is sized correctly for the application. Equally, the diode can only handle a certain voltage or current in the forward bias. The diode requires a certain voltage level to open and allow current to flow in the forward bias. Most are around 0.
If we apply a voltage less than this, it will not open to allow current to flow. But, as we increase past that, the amount of current that can flow will rapidly increase. The diodes will also provide a voltage drop into the circuit. For example when I added this diode into a simple LED circuit mounted to a breadboard, I get a voltage drop reading of 0. As mentioned we use diodes to control the direction of current flow in a circuit.
The diode can block the current and keep our components safe. We can also use them to convert AC to DC. As you might know AC or alternating current moves electrons forwards and backwards creating a sine wave with a positive and a negative half, but DC or direct current moves electrons in just one direction which gives a flat line in the positive region.
If we connect the primary side of a transformer to an AC supply and then connect the secondary side to a single diode, the diode would only allow half the wave to pass and it would block the current in the opposite direction.
One way to do that is if we connected four diodes to the secondary side, we create a full wave rectifier.
The diodes control which path the alternating current can flow along by blocking or allowing it to pass. As we just saw the positive half of the sine wave is allowed to pass but this time the negative half is also allowed to pass, although this has been inverted to turn it into a positive half also.
This gives us a better DC supply because the pulsating has greatly reduced. But we can still improve this further, we simply add in some capacitors to smooth out the ripple and eventually get it into a smooth line to closely mimic DC. To test a diode, we will need a multimeter with a diode test setting, the symbol will look like this. We highly recommend you have a good multimeter in your toolkit to help you learn as well as diagnose problems.
So we take our diode and multimeter. We connect the black wire to the end of the diode with a line. Then we connect the red wire to the opposite end. When we do this, we should get a reading on the screen. For example this model 1N diode gives a reading of 0. This is the minimum voltage it takes to open the diode to allow current to flow. If we now reverse the leads connected to the diodes, we should see OL on the screen which means outside limits. To test a diode in a circuit for voltage drop, we simply move the multimeter into the DC voltage function and then place the black probe to the stripe end and the red probe to the black end.
This will give us a reading for example of 0. Save my name, email, and website in this browser for the next time I comment. The Engineering Mindset. Home Electrical Electronics Diodes Explained. Electrical Electronics.
Motor Speed Controller Tutorial. How Optocouplers Work. Please enter your comment! Please enter your name here. You have entered an incorrect email address! Support more content. You'll like these too! Paul Evans - Jun 5, 4. Paul Evans - Jul 31, 0. You'll notice that every diode has some way no matter how tiny or hard to see to indicate which of the two pins is the cathode.
The flashiest member of the diode family must be the light-emitting diode LED. These diodes quite literally light up when a positive voltage is applied. A handful of through-hole LEDs. From left to right: a yellow 3mm , blue 5mm , green 10mm , super-bright red 5mm , an RGB 5mm and a blue 7-segment LED.
Like normal diodes, LEDs only allow current through one direction. They also have a forward voltage rating, which is the voltage required for them to light up. You'll obviously most-often find LEDs in lighting applications. They're blinky and fun! But more than that, their high-efficiency has lead to widespread use in street lights, displays, backlighting, and much more.
Other LEDs emit a light that is not visible to the human eye, like infrared LEDs, which are the backbone of most remote controls. Another common use of LEDs is in optically isolating a dangerous high-voltage system from a lower-voltage circuit.
Opto-isolators pair an infrared LED with a photosensor, which allows current to flow when it detects light from the LED. Below is an example circuit of an opto-isolator. Note how the schematic symbol for the diode varies from the normal diode. LED symbols add a couple arrows extending out from the symbol. Another very common diode is the Schottky diode. Schottky diodes are known for their low forward voltage drop and a very fast switching action.
This 1A 40V Schottky diode is …. The semiconductor composition of a Schottky diode is slightly different from a normal diode, and this results in a much smaller forward voltage drop , which is usually between 0. They'll still have a very large breakdown voltage though. Schottky diodes are especially useful in limiting losses, when every last bit of voltage must be spared. They're unique enough to get a circuit symbol of their own, with a couple bends on the end of the cathode-line.
Zener diodes are the weird outcast of the diode family. They're usually used to intentionally conduct reverse current. Zener diodes are useful for creating a reference voltage or as a voltage stabilizer for low-current applications. These diodes…. Zener's are designed to have a very precise breakdown voltage, called the zener breakdown or zener voltage. When enough current runs in reverse through the zener, the voltage drop across it will hold steady at the breakdown voltage.
Taking advantage of their breakdown property, Zener diodes are often used to create a known reference voltage at exactly their Zener voltage. They can be used as a voltage regulator for small loads, but they're not really made to regulate voltage to circuits that will pull significant amounts of current.
Zeners are special enough to get their own circuit symbol, with wavy ends on the cathode-line. The symbol might even define what, exactly, the diode's zener voltage is. Here's a 3. Photodiodes are specially constructed diodes, which capture energy from photons of light see Physics, quantum to generate electrical current. Kind of operating as an anti-LED. This photodiode has a ton of u…. A BPW34 photodiode not the quarter, the little thing on top of that. Solar cells are the main benefactor of photodiode technology.
But these diodes can also be used to detect light, or even communicate optically. For such a simple component, diodes have a huge range of uses. You'll find a diode of some type in just about every circuit. They could be featured in anything from a small-signal digital logic to a high voltage power conversion circuit.
Let's explore some of these applications. A rectifier is a circuit that converts alternating current AC to direct current DC. This conversion is critical for all sorts of household electronics. AC signals come out of your house's wall outlets, but DC is what powers most computers and other microelectronics. Current in AC circuits literally alternates -- quickly switches between running in the positive and negative directions -- but current in a DC signal only runs in one direction.
So to convert from AC to DC you just need to make sure current can't run in the negative direction. A half-wave rectifier can be made out of just a single diode. If an AC signal, like a sine wave for example, is sent through a diode any negative component to the signal is clipped out. A full-wave bridge rectifier uses four diodes to convert those negative humps in the AC signal into positive humps. DC signals. If you tore apart a wall-wart , you'd most likely see a handful of diodes in there, rectifying it up.
Can you spot the four diodes making a bridge rectifier in this wall-wart? Ever stick a battery in the wrong way? Or switch up the red and black power wires? If so, a diode might be to thank for your circuit still being alive. A diode placed in series with the positive side of the power supply is called a reverse protection diode. It ensures that current can only flow in the positive direction, and the power supply only applies a positive voltage to your circuit. This diode application is useful when a power supply connector isn't polarized, making it easy to mess up and accidentally connect the negative supply to the positive of the input circuit.
The drawback of a reverse protection diode is that it'll induce some voltage loss because of the forward voltage drop. This makes Schottky diodes an excellent choice for reverse protection diodes. Forget transistors! For example, a diode two-input OR gate can be constructed out of two diodes with shared cathode nodes. The output of the logic circuit is also located at that node. An AND gate is constructed in a similar manner. The anodes of both diodes are connected together, which is where the output of the circuit is located.
Both inputs must be logic 1 forcing current to run towards the output pin and pull it high also. If either of the inputs are low, current from the 5V supply runs through the diode. Diodes are very often used to limit potential damage from unexpected large spikes in voltage. Transient-voltage-suppression TVS diodes are specialty diodes, kind of like zener diodes -- lowish breakdown voltages often around 20V -- but with very large power ratings often in the range of kilowatts. They're designed to shunt currents and absorb energy when voltages exceed their breakdown voltage.
Flyback diodes do a similar job of suppressing voltage spikes, specifically those induced by an inductive component, like a motor. When current through an inductor suddenly changes, a voltage spike is created, possibly a very large, negative spike. A flyback diode placed across the inductive load, will give that negative voltage signal a safe path to discharge, actually looping over-and-over through the inductor and diode until it eventually dies out.
Now that your current is flowing in the right direction, it's time to put your new knowledge to good use. Whether you're looking for a starting point or just stocking up, we've got an Inventor's Kit as well individual diodes to choose from.
See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering. Take me there! Now that you've gotten a handle on diodes, maybe you'd like to further explore more semiconductors:. Need Help? Mountain Time: Shopping Cart 0 items. Product Menu. Today's Deals Forum Desktop Site. All Categories. Development Single Board Comp. Home Tutorials Diodes Diodes.
Contributors: jimblom. Introduction Once you graduate from the simple, passive components that are resistors , capacitors , and inductors, it's time to step on up to the wonderful world of semiconductors. Every electrical project starts with a circuit. Don't know what a circuit is? We're here to help.
Favorited Favorite Learn about Ohm's Law, one of the most fundamental equations in all electrical engineering. We can see electricity in action on our computers, lighting our houses, as lightning strikes in thunderstorms, but what is it?
This is not an easy question, but this tutorial will shed some light on it! Learn the basics of using a multimeter to measure continuity, voltage, resistance and current.
We've got you covered! Favorited Favorite 75 Wish List. Favorited Favorite 55 Wish List. Favorited Favorite 11 Wish List. Favorited Favorite 5 Wish List. See all diodes. Ideal Diodes The key function of an ideal diode is to control the direction of current-flow.
Real Diode Characteristics Ideally , diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward.
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