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Schottky diodes have been useful for the electronics industry, which has identified many applications in diode rectifiers because of their unique properties. Here are some major areas where they are widely used.
General-purpose rectifiers The fast switching operation of Schottky diodes makes them suitable signal rectifiers. Schottky diodes have high current density and low forward voltage drop. This minimizes energy wastage in a rectification circuit. Schottky diodes dissipate less heat and thus require smaller heat sinks. This reduces the overall cost and size of the rectifier circuit.
Clamping Schottky diodes are used as switching diodes in transistor clamping circuits. For clamping, the Schottky diode is connected between the collector and the base of the driver transistor. When turned ON, the Schottky diode delivers a high current at low bias voltage. Again, as its reverse recovery time is much shorter, the switching time of the transistor is significantly improved. Schottky diodes have been used as clamping diodes in logic circuit ICs. These ICs have LS or S included in their circuit code names, like 74LS or 74S.
Power OR circuits and SMPS As Schottky diodes have a very low forward voltage, they are beneficial in circuits where two different power supplies drive the load, such as from the mains supply and a battery. That is why Schottky diodes are frequently used in SMPS and inverter circuits.
RF mixing and detection High current density, high switching speed, low junction capacitance, and low forward voltage make Schottky diodes ideal for low-current, high-frequency applications. Schottky diodes are frequently used in diode ring mixers and RF signal detectors.
Solar cell applications As we know, solar cells are usually connected to rechargeable batteries, mostly lead-acid batteries, since a power supply must be available round the clock. Solar cells will not support the applied charge in reverse, and thus a diode is used in proportion to the solar cells.
Power rectifier Schottky barrier diodes also function as high-power rectifiers. Their high current density and low forward voltage drop mean that power wastage is lower than in normal PN junction diodes.
Choosing the Perfect Schottky Diode for Your Application
Schottky diodes are a popular choice in a wide range of applications, from power supplies to solar panels, thanks to their unique combination of low forward voltage drop, fast switching speeds, and high efficiency. Choosing the right Schottky diode is crucial for optimal performance and reliability. In this blog post, we'll walk you through the key factors to consider when selecting the perfect Schottky diode for your specific application.
Voltage rating (VR) The first step in choosing the right Schottky diode is determining the maximum voltage the diode will be exposed to in your circuit. Select a diode with a reverse voltage rating (VR) higher than this value. As a rule of thumb, choose a diode with a VR of at least 1.5 to 2 times the maximum voltage to ensure a safety margin and prevent premature failure.
Forward Current Rating (IF) Estimate the maximum current the diode will be required to handle in your application. Choose a Schottky diode with a forward current rating (IF) higher than this value. Providing a safety margin ensures reliable operation and prevents the diode from overheating or failing under high-current conditions.
Forward voltage drop (VF) One of the main advantages of Schottky diodes is their low forward voltage drop (VF), which typically ranges from 0.15V to 0.5V. This characteristic minimizes power losses and reduces heat generation. Select a diode with a low forward voltage drop that meets your voltage and current requirements for optimal efficiency.
Package type Schottky diodes come in various package types, including through-hole (e.g., DO-201, DO-41) and surface-mount (e.g., SOD-123, SMC). Consider your specific application, space constraints, thermal performance, and ease of assembly when selecting the appropriate package type.
Thermal performance Ensure that the Schottky diode you choose can handle the heat generated during operation. Check the diode's power dissipation and thermal resistance values to confirm it can effectively dissipate heat and maintain safe operating temperatures.
Reverse recovery time (trr) While Schottky diodes generally have fast reverse recovery times compared to standard diodes, it's essential to consider this parameter in high-frequency applications. Select a diode with a reverse recovery time (trr) that meets the switching speed requirements of your circuit to maximize efficiency and minimize losses.
What Is the Difference Between Schottky Diode and PN Junction Diode
A Schottky diode is a unipolar device whose current flow is entirely due to electrons. Many differences distinguish a Schottky diode from a typical PN junction diode (small-signal or rectifier diodes). The Schottky diode is constructed by joining metal with an n-type semiconductor, while the PN junction diode is constructed by joining P-type and N-type semiconductors. A PN junction diode is a bipolar device in which current flows due to electrons and holes. The forward knee voltage of the Schottky diode is much lower than that of a PN junction diode, and its reverse recovery time and reverse recovery loss are also shorter. This makes the Schottky diode a high-speed switching device compared to a typical PN junction diode. That is why the diode used in logic circuit designs is usually a Schottky diode.
Schottky diode
PN junction diode
In this diode, the junction is formed between the n-type semiconductor and the metal plate
In this diode, the junction is formed between the p-type and n-type semiconductors
The forward voltage drop is low
The forward voltage drop for pn junction diode is more
Reverse recovery loss and reverse recovery time are very less
Reverse recovery loss and reverse recovery time are more
It is a unipolar device
It is a bipolar device
The conduction of current happens only due to the movement of electrons
The conduction of current happens due to the movement of electrons and holes
Schottky Diode Working Principle
A Schottky diode, also known as a hot carrier diode, is a semiconductor diode that has a low forward voltage drop and a very fast switching action. There is a small voltage drop across the diode terminals when current flows through the diode. A normal diode will have a voltage drop between 0.6 to 1.7 volts, while a Schottky diode's voltage drop is usually between 0.15 and 0.45 volts. This lower voltage drop provides better system efficiency and higher switching speed. In a Schottky diode, a semiconductor–metal junction is formed between a semiconductor and a metal, thus creating a Schottky barrier. The N-type semiconductor acts as the cathode and the metal side acts as the anode of the diode. This Schottky barrier results in both a low forward voltage drop and very fast switching.
Schottky diodes are high-current diodes used primarily in high-frequency and fast-switching applications. They are also known as hot-carrier diodes. The term "hot-carrier" is derived from the higher energy level of electrons in the n region compared to those in the metal region. A Schottky diode is formed by joining a doped semiconductor region (usually n-type) with a metal such as gold, silver, or platinum. Rather than a pn junction, there is a metal-to-semiconductor junction, as shown in the figure below. The forward voltage drop is typically around 0.3 V because there is no depletion region as in a pn junction diode.
The Schottky diode operates only with majority carriers. There are no minority carriers and thus no reverse leakage current as in other types of diodes. The metal region is heavily occupied with conduction-band electrons, and the n-type semiconductor region is lightly doped. When forward-biased, the higher energy electrons in the n region are injected into the metal region where they give up their excess energy very rapidly. Since there are no minority carriers, as in a conventional rectifier diode, there is a very rapid response to a change in bias. The Schottky diode is a fast-switching diode, and most of its applications make use of this property. It can be used in high-frequency applications and in many digital circuits to decrease switching times.
Construction of Schottky Diode
A Schottky diode is constructed by joining a metal electrode with a lightly doped, n-type semiconductor. Due to the metal-semiconductor junction, a Schottky diode has no depletion region. The n-type material must be lightly doped; otherwise, the device will fail to operate as a rectifier. In a Schottky diode, current flows due to majority charge carriers, i.e., electrons, when forward biased. In reverse bias, the conduction of reverse saturation current stops immediately because there are no minority charge carriers (i.e., holes) in the construction of a Schottky diode.
The most straightforward construction of a Schottky diode is a point contact between a metal wireanda lightly-doped n-type semiconductor material. This type of construction is simple but notveryreliable. Another common manufacturing technique is usingavacuum to deposit metal ontothen-type semiconductor material. First of all, the semiconductor surface is protected by an oxide ring. Then, the metal is deposited onto the semiconductor surface using a vacuum technique. The oxide ring avoids breakingthe bond betweenthe metal surfaceandthe semiconductor due to electric fields established in reverse bias conditions. The most common metal used in the construction of Schottky diodes is silicide.Silicideis known to have very low ohmic resistance, which makes it the most preferred metal for Schottky diodes. Other metals that may be used in constructingaSchottky diode are aluminum and platinum. The selection of the metal and doping level of the n-type material plays an essential role in determining the diode’s forward voltage.
Specifications of Schottky Diode
The following specifications are worth noting in the datasheet of any Schottky diode. Forward voltage: This is the forward bias voltage at which the current through the diode starts rising exponentially. This is typically from 150 mV to 450 mV for all Schottky diodes.
Capacitance: This is the diode capacitance exhibited byaSchottkydiode. It is in the picofarads range. In an equivalent model ofaSchottky diode, the capacitor must be replaced by the same capacitance value.
Reverse leakage current: This is the typical reverse current value whenareverse voltage is applied. It is specified for a given temperature. The reverse leakage current increases as the temperature rises.
Reverse breakdown voltage: This is the peak inverse voltage at which the Schottky diodebreaks downin reverse bias.
Reverse recovery time: The switching time required by the Schottky diode to transition between the states of ON and OFF. It is typically in picoseconds or nanoseconds.
Working temperature: The operating temperature that the metal-semiconductor junction can tolerate.
How Does a Schottky Diode Maintain a Constant Voltage
A fundamental property of all types of diodes (silicon, germanium, Schottky, LEDs, Zener ...) is to maintain a relatively constant voltage when the current through them varies. How do they do that? This question can be answered specifically by considering the processes in the semiconductor PN junction. Also, it would be interesting to explain this on a conceptual level by revealing the basic idea. This "philosophical" approach has several advantages: first, it does not require in-depth knowledge of semiconductor devices; second, it would be applicable to all 2-terminal devices that have this property. I will do this using the concept of "dynamic resistance". In the most general sense, a diode behaves like a resistor that interferes with current, creating a voltage drop and heat loss. In the initial sloping part of its IV curve, this "resistor" has a relatively constant high resistance. And if it were really a resistor, the curve would continue in the same direction. When the current I increases, the diode decreases its static resistance R with the same rate of change. So, the voltage drop across the diode V = I×R does not change.
FAQ
Q: What is a Schottky diode used for?
A: Schottky diodes are used as switches in fast-clamp diode applications. In this application, the base junction is forward biased. With Schottky diodes, the turn-off time is significantly reduced and the speed of the circuit is increased.
Q: What is the difference between a Schottky diode and a normal diode?
A: Generally, Schottky diodes are preferred when low forward voltage drop, high switching speed, and high-frequency operation are important. However, conventional diodes are better when high reverse breakdown voltage, low reverse leakage current, and high reliability are essential.
Q: Why is a Schottky diode used instead of a general diode?
A: While standard silicon diodes have a forward voltage drop of about 0.7 V and germanium diodes 0.3 V, Schottky diodes' voltage drop at forward biases of around 1 mA is in the range of 0.15 V to 0.46 V (see the 1N5817 and 1N5711), which makes them useful in voltage clamping applications andforprevention of transistordamage.
Q: What are Zener and Schottky diodes?
A: A Schottky diode has a type of junction that has a low forward voltage and very fast switching action. These properties make it attractive for a lot of applications. A Zener diode has a junction that has a very specific reverse voltage breakdown.
Q: Can I replace a Schottky diode with a normal diode?
A: Generally yes if the voltage and current ratings are similar, and you will getalower forward voltage drop. Schottky diodes are not available in high voltage ratings, though, so you might consider an SBS diode, which hasalowish drop and is available at higher voltages.
Q: What is the most common application for Schottky diodes?
A: A Schottky diode is primarily used for rectification in high-power applications. Commercial Schottky barrier diodes (SBDs) provide a low forward voltage drop, fast reverse recovery time, high switching speed, and enough thermal stability.
Q: What is a Schottky diode also known as?
A: The Schottky diode, also known asahot carrier diode, is a semiconductor diode with a low forward voltage drop and a very fast switching action.
Q: Why is a Schottky diode faster?
A: The diode does not use a p-n junction but a junction with a type of metal on one side and an n-type semiconductor on the other. This type of junction is called a Schottky junction. The Schottky barrier diode has an extremely low VF and an extremely high speed because it does not use holes.
Q: How do I choose a Schottky diode?
A: Choosing a Schottky diode with a low forward-voltage drop is beneficial when the DC diode current is high. However, low VF usually means higher diode capacitance, and high capacitance effects boost efficiency more at light currents.
Q: What is the advantage of a Schottky diode?
A: Following are the advantages ofaSchottky diode: The capacitance of the diode is low as the depletion region of the diode is negligible. The reverse recovery time of the diode is very fast, that is, the change from ON to OFF state is fast. The current density of the diode is high as the depletion region is negligible.
Q: What is the problem with Schottky diodes?
A: Schottky diodes tend to have a high reverse leakage current. This can lead to problems with any sensing circuits that may be in use. Leakage paths into high impedance circuits can give rise to false readings. This must therefore be accommodated in the circuit design.
Q: Is a Schottky diode a rectifier?
A: In the most basic sense, a Schottky barrier rectifier (or simply Schottky diode) operates in the same manner as a typical semiconductor diode made from Si or Ge. However, its primary purpose is to provide rectification, i.e., allow current to flow only easily along one specific direction.
Q: Why use a Zener diode?
A: The zener diode is used as a shunt voltage regulator for regulating voltage across small loads. The Zener diode is connected parallel to the load to make it reverse bias, and once the Zener diode exceedstheknee voltage, the voltage across the load will become constant.
Q: Why is it called a Zener diode?
A: The device is named after American physicist Clarence Zener, who first described the Zener effect in 1934 in his primarily theoretical studies ofthebreakdown of electrical insulator properties. Later, his work led to the Bell Labs implementation of the effect intheform of an electronic device, the Zener diode.
Q: How do I know if my Schottky diode is bad?
A: A “buzz” or “beep” will be produced by the multimeter. If the Schottky diode is not working properly, then no sound will be produced. Now, interchange the leads of the multimeter. If the meter does not make any noise, then the diode works well.
Q: What can replace a Schottky diode?
A: SBRs can directly replace Schottky diodes in the secondary stages of ac-dc power supplies such as "silver-box" computer power supplies.
Q: How much voltage is lost by a Schottky diode?
A: The Schottky diode consumes less voltage to turn on compared to traditional silicon diodes. A Schottky diode will drop around 0.2 to 0.3 volts across the terminals compared to conventional diodes, which drop about 0.6 to 0.7 volts.
Q: Are Schottky diodes more expensive?
A: Also, due to the Schottky diode being fabricated with a metal-to-semiconductor junction, it tends to be slightly more expensive than standard pn-junction silicon diodes which have similar voltage and current specifications.
Q: Are Zener diode and Schottky diode the same?
A: Schottky Diodes are made up of a metal electrode attached to an N-type semiconductor. Schottky diodes have no depletion layer and are classified as unipolar devices. Zener diodes are a modified form of PN silicon diode used extensively for voltage regulation.
Q: Where is a Shockley diode used?
A: The primary application for Shockley diodes is to control a silicon-controlled rectifier (SCR), which is a bistable switch. An SCR is just a Shockley diode with a gate connection to the p-type layer in the NPN stack of a Shockley diode.
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