## An answer to your question! #14 “What is the difference between the different types of diodes?”

Sorry everyone! This post was made in its incomplete state…..everything should be right in the world now!

I would like to know what the difference is between the various types of Diodes. As I understand it, a diode limits voltage to going in only one direction. Yet there are all kinds of different diodes; Zener, Schottky, Rectifier… Its very confusing!

Whenever I have a question pertaining to electronics and circuit design, I always find myself grabbing my copy of “The Art of Electronics” as Paul Horowitz and Winfield Hill do an awesome job with their explanations. So here it goes!

Diodes are classified as passive non-linear devices that limit the flow of reverse current, kind of like a one-way door. Each type of diode, as you have listed, carry different characteristics that allow them to be used in a wide range of ways. When you look at the specs of a diode you will see a bunch of common terminology that describes the way the device behaves. They are:

• Forward voltage drop (Vf)
• The amount of voltage that is “dropped” or lost when current is passed through the device. The drop non-linearly proportionate to the amount of current flowing and can be determined by analyzing the diode’s V-I curve.
• Forward current (If)
• The quantity of current flow the diode is capable of handling.
• Reverse breakdown voltage (Vr)
• When a reverse voltage is applied to the diode, it limits the current flow. If the maximum reverse voltage is reached the diode will breakdown and allow current to flow in the reverse direction.
• Reverse leakage current (Ir)
• The quantity of current that flows in the reverse direction when a reverse voltage is applied.
• Recovery time
• The amount of time required for the diode to return to its normal operating state after the reverse breakdown voltage has been achieved.

Most of the diodes we use today are semiconductors and resemble 2/3 of a transistor with only a P and N junction. The most common (other then LEDs) are:

• General purpose rectifier:
• A super popular PN is the 1N4001 – 1N4007 series diodes used in reverse polarity circuit protection. This category of diode has relatively high forward drop, about 1.0V, but can have a high breakdown voltage, ~200 – 1000V.
• Schottky:
• Have a much lower forward voltage drop, about 0.25V, and a very fast recovery time. Their downside is that they have a pretty low breakdown voltage ~20 – 40V. This makes them good for low voltage rectifier applications.
• Signal:
• A popular signal diode is the 1N914 type. These diodes are designed to switch and recover at very high speeds, but have relatively low breakdown voltages, <100V, and low forward currents, ~100ma.
• Zener:
• Are typically used as a means of maintaining a constant voltage by providing them with a constant current, usually through a series resistor. A lot of voltage references use Zeners. (Harry in the comment section goes a bit more in depth, thank you by the way!)

There are also a ton of resources online that give much more detailed explanations:

I hope this answers your question and gives you a better idea as far as diodes is concerned!

Next up is Stephanie with a question about undergraduate degrees in STEM education!

Don’t forget, everyone is invited to ask a question!

“Ask an Educator” questions are answered by Adam Kemp, a high school teacher who has been teaching courses in Energy Systems, Systems Engineering, Robotics and Prototyping since 2005.

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## 1 Comment

1. Filling in that last category: Zener diodes are designed with a specific, and usually relatively low, reverse breakdown voltage, commonly 1.25 volts. Because of this, when they are connected backwards across a voltage (with a resistor put in line) they hold that fixed voltage across them, despite fluctuations in the voltage powering them. They are commonly used as reference devices for voltage regulators or analog to digital converters.

Comment by Harry — March 6, 2012 @ 10:31 am

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