I’ve been asked a few times – what is a diode?
Well, a diode is an electronic component that conducts current in one direction and blocks current from flowing in the other direction.
The diode symbol looks like this:
How To Connect A Diode
Let’s look at an example.
In the circuit above the diode is connected in the right direction. This means current can flow through it so that the 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?
Diodes are very often used in power supplies. From the power outlet in your wall you get alternating current (AC). A lot of the devices we use need direct current (DC). To get DC from AC we need a rectifier circuit. It’s a circuit that converts from alternating current (AC) to direct current (DC). Diodes are the main components in rectifier circuits.
How a Diode Works
The diode is created from a PN junction. You get a PN junction by taking negative doped and positive 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.
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 0.7V.
- The diode have 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 diodes, rectifier diodes, zener diodes and Light-Emitting Diodes (LED). Signal and rectifier diodes are pretty much the same thing 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.
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