Diodes are a critical part of many electronic devices. They convert alternating current (AC) into direct current (DC). AC signals travel from the wall outlets to your computer and other electronics, but DC is what powers most microelectronics. The key to converting AC to DC is making sure that the current can’t run in the wrong direction, which is where diodes come in.
There are a number of different types of diodes, each with its own unique properties. The most common type is a rectifier diode, used in circuits that convert AC into DC.
When a diode is forward biased, current flows from the anode (positive) to the cathode (negative). The current flowing through the diode is proportional to the voltage across the anode and inversely proportional to the voltage across the cathode.
One of the most common uses for a diode is to protect a circuit from reversed connection problems. If the battery in a device isn’t inserted correctly, for example, reversed current can travel from the battery into the rest of the circuit, which could damage other components or cause an electrical short.
A blocking diode is similar to a blocking resistor, but instead of preventing reversed current from flowing, it stops current that’s coming in the opposite direction. A diode can also be a capacitor that protects a circuit from voltage transients, or spikes in the power supply.
The most important thing to remember about diodes is that they act as one-way switches. In an ideal diode, the current flowing through it should flow in only one direction and stop if it starts to flow in the opposite direction.
In reality, however, this isn’t quite true for all diodes. Most don’t block out all reverse current, and they can actually consume a bit of power when conducting forward current.
Some diodes can even be designed to work in reverse bias. This is called a Zener diode, and it’s especially useful in stabilizing small direct voltages.
Most of the time, a Zener diode will be connected to a load resistor to limit its current and to stabilize the voltage. The current and voltage in the resistor should be equal to or less than the input voltage so that the diode doesn’t draw more power than needed.
Another common type of diode is a photodiode, which can be treated as little tiny photovoltaic solar cells when illuminated. When a photodiode is illuminated with bright light, it generates a small amount of current that you can use in your circuits.
A light-emitting diode, or LED, is another specialized kind of diode that lights up when it’s biased in the forward direction. A typical LED produces a glow from light-emitting holes that’re in the diode’s semiconductor layer.
Diodes can be made with any material, but most are made with two different semiconductor materials that meet at a junction. This material is either n-type or p-type. N-type materials have a surplus of positive charge carriers in the form of holes and a deficit of negative charge carriers in the form of electrons.