What makes a diode work

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.

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These cookies do not store any personal information. Non-necessary Non-necessary. The terminal entering the flat edge of the triangle represents the anode. Above are a couple simple diode circuit examples. On the left, diode D1 is forward biased and allowing current to flow through the circuit. In essence it looks like a short circuit. On the right, diode D2 is reverse biased. Current cannot flow through the circuit, and it essentially looks like an open circuit.

Unfortunately, there's no such thing as an ideal diode. But don't worry! Diodes really are real, they've just got a few characteristics which make them operate as a little less than our ideal model Ideally , diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward.

Unfortunately, actual diode behavior isn't quite ideal. Diodes do consume some amount of power when conducting forward current, and they won't block out all reverse current. Real-world diodes are a bit more complicated, and they all have unique characteristics which define how they actually operate. The most important diode characteristic is its current-voltage i-v relationship. This defines what the current running through a component is, given what voltage is measured across it.

Resistors, for example, have a simple, linear i-v relationship Ohm's Law. The i-v curve of a diode, though, is entirely non -linear. It looks something like this:. The current-voltage relationship of a diode. In order to exaggerate a few important points on the plot, the scales in both the positive and negative halves are not equal.

In order to "turn on" and conduct current in the forward direction, a diode requires a certain amount of positive voltage to be applied across it. The typical voltage required to turn the diode on is called the forward voltage V F. It might also be called either the cut-in voltage or on-voltage. As we know from the i-v curve, the current through and voltage across a diode are interdependent.

More current means more voltage, less voltage means less current. Once the voltage gets to about the forward voltage rating, though, large increases in current should still only mean a very small increase in voltage. If a diode is fully conducting, it can usually be assumed that the voltage across it is the forward voltage rating.

A multimeter with a diode setting can be used to measure the minimum of a diode's forward voltage drop. A specific diode's V F depends on what semiconductor material it's made out of. Typically, a silicon diode will have a V F around 0.

A germanium-based diode might be lower, around 0. The type of diode also has some importance in defining the forward voltage drop; light-emitting diodes can have a much larger V F , while Schottky diodes are designed specifically to have a much lower-than-usual forward voltage.

If a large enough negative voltage is applied to the diode, it will give in and allow current to flow in the reverse direction. This large negative voltage is called the breakdown voltage. Some diodes are actually designed to operate in the breakdown region, but for most normal diodes it's not very healthy for them to be subjected to large negative voltages.

All of the above characteristics should be detailed in the datasheet for every diode. For example, this datasheet for a 1N diode lists the maximum forward voltage 1V and the breakdown voltage V among a lot of other information :. A datasheet might even present you with a very familiar looking current-voltage graph, to further detail how the diode behaves. This graph from the diode's datasheet enlarges the curvy, forward-region part of the i-v curve.

Notice how more current requires more voltage:. That chart points out another important diode characteristic -- the maximum forward current. Just like any component, diodes can only dissipate so much power before they blow. All diodes should list maximum current, reverse voltage, and power dissipation.

If a diode is subject to more voltage or current than it can handle, expect it to heat up or worse; melt, smoke, Some diodes are well-suited to high currents -- 1A or more -- others like the 1N small-signal diode shown above may only be suited for around mA.

That 1N is just a tiny sampling of all the different kinds of diodes there are out there. Next we'll explore what an amazing variety of diodes there are and what purpose each type serves. Standard signal diodes are among the most basic, average, no-frills members of the diode family.

They usually have a medium-high forward voltage drop and a low maximum current rating. A common example of a signal diode is the 1N This is a very common signal diode - 1N Use this for signals up to mA of current.

Very general purpose, it's got a typical forward voltage drop of 0. A small-signal diode, the 1N Notice the black circle around the diode, that marks which of the terminals is the cathode. A rectifier or power diode is a standard diode with a much higher maximum current rating.

This higher current rating usually comes at the cost of a larger forward voltage. The 1N is an example of a power diode. A 1N PTH diode. This time a gray band indicates which pin is the cathode. And, of course, most diode types come in surface-mount varieties as well. 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.