Learn how Schottky diodes operate in RF circuits, generators, and motor drives with their low forward voltage drop and fast switching speeds.

Like other diodes, Schottky diodes control the direction of current flow in a circuit. These devices are like one-way streets in the electronic world, allowing current to flow only from the anode to the cathode. However, unlike standard diodes, Schottky diodes are known for their low forward voltage and fast switching capability. This makes them ideal for RF applications and any device with low voltage requirements. Schottky diodes have a variety of uses, including:

Power supply rectification: Schottky diodes can be used in high power applications due to their low forward voltage drop. These diodes will waste less power and may reduce the size of the heat sink.
Multiple power supplies: Schottky diodes can also help keep power supplies separated in dual power supply setups (e.g. mains and battery).
Solar Cells: Schottky diodes have a low forward voltage drop, which helps maximize solar cell efficiency. They also help protect the battery from reverse charge.
Clamping: Schottky diodes can also be used as clamps in transistor circuits such as 74LS or 74S logic circuits.

Advantages and Disadvantages of Schottky Diodes

One of the main advantages of using a Schottky diode over a regular diode is its low forward voltage drop. This allows the Schottky diode to consume less voltage than a standard diode, with a junction voltage of only 0.3-0.4 V. In the graph below, you can see that the current in the Schottky diode begins to increase significantly at a forward voltage drop of about 0.3 V. For a standard diode, this increase in current does not take effect until about 0.6 V. For a standard diode, this current increase does not take effect until about 0.6V.

In the figure below we have two circuits to illustrate the benefits of a lower forward voltage drop. The left circuit contains a conventional diode and the right circuit contains a Schottky diode. Both are powered by a 2V DC supply

Conventional diodes consume 0.7V, leaving only 1.3V to power the load. The Schottky diode has a lower forward voltage drop and consumes only 0.3V, leaving only 1.7V to power the load. If our load requires 1.5V, then only a Schottky diode is suitable.

Other advantages of using a Schottky diode over a regular diode

Faster recovery time: The small amount of charge stored in a Schottky diode makes it ideal for high-speed switching applications.
Less noise: Schottky diodes produce less unwanted noise than typical PN junction diodes.
Better performance: Schottky diodes consume less power and can easily meet the requirements of low-voltage applications.
Schottky diodes have some disadvantages to be aware of. Reverse biased Schottky diodes experience higher reverse currents than conventional diodes. This results in more leakage current when connected in reverse.

The maximum reverse voltage of a Schottky diode is also lower than that of a standard diode, typically 50V or less. Once this value is exceeded, the Schottky diode breaks down and begins to conduct a large amount of current in reverse. However, even before this reverse value is reached, the Schottky diode will still leak a small amount of current like any other diode.

How Schottky Diodes Work

A typical diode combines a p-type semiconductor with an n-type semiconductor to form a pn junction. In a Schottky diode, a metal replaces the p-type semiconductor. This metal can be platinum, tungsten, molybdenum, gold, etc.

When a metal is combined with an n-type semiconductor, an ms junction is formed. This junction is called a Schottky barrier. The behavior of the Schottky barrier will vary depending on whether the diode is unbiased, forward biased or reverse biased.

Unbiased State

In an unbiased state, free electrons will move from the n-type semiconductor to the metal in order to establish balance. This flow of electrons created the Schottky Barrier where negative and positive ions meet. Free electrons will need a greater supplied energy than their built-in voltage to overcome this barrier.

Forward-Biased State

Connecting the positive terminal of a battery to the metal and the negative terminal to the n-type semiconductor will create a forward-biased state. In this state, electrons can cross the junction from n-type to metal if the applied voltage is greater than 0.2 volts. This results in a flow of current that’s typical for most diodes.

Reverse-Biased State

Connecting the negative terminal of a battery to the metal and positive terminal to the n-type semiconductor will create a reverse-biased state. This state expands the Schottky Barrier and prevents the flow of electric current. However, if the reverse bias voltage continues to increase this can eventually break down the barrier. Doing so will allow current to flow in the reverse direction and may damage the component.

Schottky diodes are the way to go! These diodes are well known for their low forward voltage drop and quick switching speeds. Whether they’re used in solar cells or power rectification, you can’t beat the low 0.3V voltage drop and added efficiency.

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