• Sarah Whiteford

Wednesday Write-up: Diodes Part 1

Over the next few weeks, we are going to talk about the humble diode, one of the most commonly used and high-reliability silicon devices we have at our disposal! In particular, we are going to discuss what they are, how they are used in dynamically positioned vessels, what their strengths and weaknesses are, and what other options are available.

What is a diode?

Source: Fluke.com

A diode is a type of semiconductor electrical component that works as a one-way valve.

This makes it very useful in such applications as rectification of AC current into DC current and preventing stray back-flow currents from damaging sensitive electrical components, such as microprocessors.

How does it work?

Being a semiconductor means that a diode is conductive when current passes through one side but is not conductive when the current tries to pass through the other. A diode - the main material of which is silicon - is able to function in this way by having 2 contacts, one of which is the negative pole (cathode) and the other being the positive pole (anode). One of these contacts will be made of normal conductive material or can be made highly conductive by adding arsenic or phosphorus in a process known as doping. The other contact will have another material doped in that raises the electrical resistance to current flow. The most common materials for this being boron or gallium. When mixed in they form electrical ‘holes’ as in pockets of severe resistance that does not allow the current to flow normally.

Source: Fluke.com

Furthermore, the silicon can be made to simply have air pockets to raise the resistance, but these types of diodes are not as reliable. Either the anode or cathode can be made to be the more resistant side depending on the diode’s intended use. By applying current to the more resistant side of the diode the electrical holes are filled thus allowing the current to continue to flow through the diode.

How can it fail?

The most common way a diode can fail is either by being exposed to a current beyond the diode’s rating or by thermal decay. If a current that is too strong is applied it will simply jump the electrical ‘holes’. Or if the diode is subjected to high temperatures the interior structure falls apart. For these reasons, it is vital that diodes be properly rated for their application and operating environment.

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