Every diode has two terminals -- connections on each end of the component -- and those terminals are polarized , meaning the two terminals are distinctly different.
It's important not to mix the connections on a diode up. The positive end of a diode is called the anode , and the negative end is called the cathode. Current can flow from the anode end to the cathode, but not the other direction. If you forget which way current flows through a diode, try to remember the mnemonic ACID : "anode current in diode" also anode cathode is diode. The circuit symbol of a standard diode is a triangle butting up against a line. As we'll cover in the later in this tutorial , there are a variety of diode types, but usually their circuit symbol will look something like this:.
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. It has a nice explanation and models as well as relevant circuits. Several of the answers don't strictly respond to the question that was asked. Add a comment.
Active Oldest Votes. Specifically, above a certain "threshold" voltage, it only requires a very small increase in voltage to increase the current to astronomical levels: CC image from openwetware. Edit what's the purpose of including a garden-variety diode not an LED in a circuit? For example, To protect a circuit from a battery installed in reverse.
To form a full-bridge rectifier circuit using 4 diodes to convert AC power to DC. In a peak detector circuit. The Photon The Photon k 3 3 gold badges silver badges bronze badges. The whole curve should be shifted down with the knee on the RHS in the 4th quadrant which is the regime in which PV cells operate. Operation in the 4th quadrant implies the component is delivering power to the rest of the circuit, which diodes don't do.
Except of course photodiodes and maybe PV cells , when they have optical power applied to them. And you are also correct in that the curve shifts down with applied light. I'm just so used to looking at these curves with applied light I forgot about the curve shift. But what's the purpose of including a garden-variety diode not an LED in a circuit? Olin Lathrop Olin Lathrop k 36 36 gold badges silver badges bronze badges. Keya Keya 9 1 1 bronze badge. Sign up or log in Sign up using Google.
Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Latest Articles in "Industry News". A diode may be the simplest of all semiconductor components, however, it performs many critical functions, including the control of the flow of an electrical current.
A diode is a device that allows current to flow in one direction but not the other. This is achieved through a built-in electric field. Although the earliest diodes consisted of red-hot wires running through the middle of a metal cylinder which itself was located inside of a glass vacuum tube, modern diodes are semiconductor diodes.
As the name suggests, these are made from semiconductor materials , primarily doped silicon. I—V current vs. Despite being nothing more than a simple two-pin semiconductor devices, diodes are vital to modern electronics.
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