Electricity can only run in one direction through a diode. When a voltage is connected in the non-conductive direction, the current will be blocked by the diode.

The symbol of a diode

The polarity

Because a diode only transmits electricity in one direction, it is important that we orient the diode correctly. A diode will only be a good conductor when the current flows from the anode(+) to the cathode(-) of the diode. The cathode(-) of the diode will be on the side of the colored ring. This is clearly shown in the picture below:


A diode will only be able to conduct current when the anode is connected on the positive side and the cathode on the negative side of the voltage source.

When should you use a diode?

In our workshop, diodes are by far the most frequently used in the form of LEDs. These are diodes that emit light when a current flows through them.

There are also other applications for diodes. When setting up in the configuration of a rectifier, they can be used to convert alternating current to direct current, for example. However, for most beginning circuit designers, the diode will rarely be important.

Some porperties

So a diode only allows the current to flow in one direction. However, even in the direction of flow, the diode will only run at a certain voltage. With a silicone diode, the most common variant, the voltage must be at least 0.6 volts. This voltage is also referred to as the permeability voltage. The forward voltage also indicates how many volts the diode will use. So if we would make a circuit with a light, a (silicone) diode, and a 3-volt battery, then the light will get a voltage of 2.4 volts.

In addition, a diode also has a break-through voltage. The breakthrough voltage indicates how many volts a diode can withstand in the reverse direction (the non-conductive direction) until current will flow through it. So it is actually the same as the breakthrough voltage but in the other direction. However, the forward voltage will be much higher than the forward voltage.

So it is important to take the breakdown voltage into account when selecting a diode. When the breakdown voltage is exceeded, a short circuit can occur.

However, this phenomenon can also be put to good use. An example of this is the flyback diode. This is a diode that is connected to a motor, it is connected in the direction that it will not conduct. However, when the motor causes a large voltage spike, the breakdown voltage of the diode will be exceeded. The diode will let current through until this peak is gone. Because of this, this high voltage will not pass through the other components, so the circuit is protected by the diode.

Also, when the breakdown voltage is not reached, the diode will still let a little current through in the reverse direction. This current is also called the leakage current. In general, the leakage current will only be a few milliamps.

Absolute maxima

Despite the breakdown voltage and the leakage current, a diode, like any component, also have absolute maximums. These indicate the limits below which we have to remain confident that the diode will continue to work. These include, for example, the maximum temperature and the maximum voltage the component can have.