What Is a Schottky Diode?

A Schottky diode is a diode that uses a metal-semiconductor junction to produce rectifying behavior.

Unlike a conventional silicon PN diode, which uses a semiconductor p-n junction, the Schottky structure produces different electrical characteristics that are particularly useful in high-speed and low-voltage applications.

Two of its most important characteristics are:

• Relatively low forward-voltage drop
• Very fast switching behavior

Schottky Diode Symbol

Anode                         Cathode
  A                              K
  │                              │
───|>|───────────────────────────

The exact graphical representation of the Schottky symbol includes modified cathode markings. The actual schematic symbol should be checked when drawing or interpreting a circuit diagram.

The physical cathode of many Schottky diodes is identified by a band or stripe, but the manufacturer's datasheet should be consulted when the marking is unclear.

How a Schottky Diode Works

The metal-semiconductor junction in a Schottky diode produces a different charge-storage behavior from a conventional PN junction.

This is one of the reasons Schottky diodes can switch very quickly and have very little reverse-recovery charge compared with many conventional PN diodes.

When forward biased, the diode conducts current. When reverse biased, it blocks current subject to its leakage and reverse-voltage characteristics.

Low Forward Voltage

One of the main advantages of Schottky diodes is their relatively low forward-voltage drop.

Depending on the particular device and operating current, the forward voltage can often be substantially lower than that of a conventional silicon PN diode.

Lower forward voltage can reduce conduction losses.

P ≈ VF × IF

For example, if a diode has a forward voltage of 0.4 V and carries 5 A:

P ≈ 0.4 × 5
P ≈ 2 W

The actual loss must be determined from the manufacturer's forward-current characteristic and operating conditions.

Fast Switching

Schottky diodes are known for fast switching because they do not have the same minority-carrier charge-storage mechanism associated with conventional PN junctions.

This makes them useful in high-frequency switching circuits where diode reverse-recovery losses can be significant.

Applications include:

• Switch-mode power supplies
• DC-DC converters
• High-frequency rectifiers
• Clamping circuits
• Logic circuits
• RF applications

Reverse-Recovery Characteristics

A conventional PN diode can continue conducting briefly after its polarity is reversed because of stored charge in the junction.

Schottky diodes do not rely on minority-carrier storage in the same way. Consequently, their reverse-recovery behavior is generally much faster and has very low stored charge.

This can reduce switching losses and unwanted current spikes in suitable circuits.

Reverse Leakage Current

One disadvantage of many Schottky diodes is higher reverse leakage compared with conventional silicon PN diodes of similar ratings.

Leakage also tends to increase significantly with temperature.

This should be considered in:

• High-temperature equipment
• Battery-powered circuits
• Low-current circuits
• Precision circuits
• High-impedance circuits

Reverse-Voltage Rating

Schottky diodes are available in many reverse-voltage ratings, but their maximum reverse voltage is often lower than that of some conventional silicon rectifier families.

The maximum reverse voltage in the circuit must therefore be checked carefully before selecting a Schottky diode.

A low forward voltage does not mean that the diode can tolerate a high reverse voltage.

Schottky Diodes in Power Supplies

Schottky diodes are particularly useful in switching power supplies because both low forward voltage and fast switching can improve efficiency.

They can be found in:

• Buck converters
• Boost converters
• Flyback converters
• Forward converters
• DC-DC modules
• Low-voltage power supplies

Schottky Diodes in Buck Converters

In an asynchronous buck converter, a Schottky diode can provide the freewheeling path when the main switching transistor is turned off.

        Switch
Vin ──────┬──────
          │
          ├──────── L ───── Load
          │
         |<|
       Schottky
          │
         GND

The low forward voltage can reduce conduction losses during the freewheeling interval.

The exact diode requirements depend on the converter's input voltage, output voltage, switching frequency, load current, and topology.

Schottky Diodes in DC-DC Converters

Low-voltage DC-DC converters benefit particularly from low forward voltage because the diode drop can represent a significant percentage of the output voltage.

For example, a 0.4 V drop is much more significant in a 3.3 V power supply than in a 50 V supply.

This is one reason Schottky diodes are frequently found in low-voltage switching converters.

Schottky Rectifiers

Schottky diodes can be used as rectifiers where their voltage and current ratings are suitable.

They are particularly useful for:

• Low-voltage rectification
• High-frequency rectification
• Switching power supplies
• Battery-powered equipment
• High-efficiency converters

At higher reverse voltages, other diode technologies may provide a more appropriate balance of voltage rating, leakage, switching performance, and cost.

Schottky Diodes for Reverse-Polarity Protection

A Schottky diode can be connected in series with a power input to provide reverse-polarity protection.

Supply + ───|>|──── Circuit +
Supply - ────────── Circuit -
```


Because the forward voltage can be relatively low, the power loss may be
lower than with a conventional silicon diode.



The diode still dissipates power, however, so the current and thermal
conditions must be considered.

Schottky Diodes as Clamp Diodes

Schottky diodes can be used for voltage clamping because their relatively low forward voltage allows a signal or switching node to be limited at a lower voltage than with a conventional silicon diode.

They are sometimes used to protect sensitive semiconductor inputs and switching nodes.

The clamp current must remain within the diode's specified limits.

Schottky Diodes in Logic Circuits

Schottky diodes have historically been used in high-speed logic circuits.

The Schottky junction can be used to prevent certain transistor junctions from becoming deeply saturated, helping improve switching speed in some bipolar logic families.

Modern digital systems generally use integrated logic technologies rather than discrete Schottky diodes for most logic functions, but the underlying principle remains important.

Schottky Diodes in RF Circuits

Small Schottky diodes can operate effectively at high frequencies because of their fast response and suitable junction characteristics.

Applications include:

• RF detectors
• Envelope detectors
• Mixer circuits
• RF switching
• Signal detection
• Microwave circuits

For RF applications, junction capacitance and package parasitics must also be considered.

Schottky Diodes as RF Detectors

A Schottky diode can rectify relatively small RF signals, making it useful in detector circuits.

Because the forward voltage can be relatively low, the diode can be useful for detecting low-level signals under appropriate circuit conditions.

Detector performance depends on diode characteristics, signal frequency, signal amplitude, impedance, and the surrounding detector circuit.

Schottky Diode Types

Schottky diodes are available in several forms designed for different applications.

Small-Signal Schottky Diodes

Used for low-current switching, detection, clamping, and RF applications.

Power Schottky Diodes

Designed for higher current and power applications such as switching converters and rectifiers.

Dual Schottky Diodes

Some packages contain two Schottky diodes internally. The internal configuration may be common-cathode, common-anode, or independent.

The internal connection must be checked in the datasheet before installation.

Common Schottky Diode Examples

Several Schottky diode families are widely used in electronic circuits. Examples include:

• 1N5817
• 1N5818
• 1N5819
• SS14
• SS34
• SR-series power Schottky devices

These parts do not all have the same ratings. Always verify the exact manufacturer's datasheet before selecting one for a circuit.

Schottky Diode vs Silicon Diode

Schottky Diode vs Fast-Recovery Diode

Power Dissipation

Even with a low forward voltage, a power Schottky diode can dissipate significant heat at high current.

A simplified estimate is:

P ≈ VF × IF

For example:

VF = 0.5 V
IF = 10 A

P ≈ 0.5 × 10
P ≈ 5 W

Five watts of heat requires appropriate thermal management. The actual power loss depends on the diode's forward characteristic, temperature, duty cycle, and operating conditions.

Temperature Effects

Temperature has a significant effect on Schottky diode behavior.

In particular, reverse leakage can increase considerably as the junction temperature rises.

Thermal design should therefore consider:

• Ambient temperature
• Junction temperature
• Forward current
• Power dissipation
• PCB copper area
• Heatsink requirements

Testing a Schottky Diode

A digital multimeter in diode-test mode can perform a basic test.

Forward Test

• Red probe → anode
• Black probe → cathode
• A relatively low forward-voltage reading should normally appear

Reverse Test

• Red probe → cathode
• Black probe → anode
• The meter should normally indicate an open or very high reverse reading

The exact forward voltage varies with device type, current, temperature, and meter test current.

A Schottky diode should not be declared faulty merely because its forward reading is lower than that of a silicon PN diode.

Common Schottky Diode Faults

Selecting a Schottky Diode

When selecting a Schottky diode, consider the complete set of operating requirements.

• Maximum reverse voltage
• Average forward current
• Peak and surge current
• Forward voltage at the actual operating current
• Reverse leakage
• Switching characteristics
• Junction capacitance
• Operating temperature
• Power dissipation
• Package

For switching power supplies, it is especially important to check the forward-voltage curve at the expected current rather than relying only on a single headline specification.

Choosing the Reverse-Voltage Rating

Determine the maximum reverse voltage that the diode will experience during normal operation and during expected transients.

The selected diode should have an appropriate reverse-voltage rating with suitable design margin.

Do not choose a Schottky diode solely because it has a low forward voltage. A device with insufficient reverse-voltage capability can fail even when its current rating is adequate.

Choosing the Current Rating

Determine the actual current waveform through the diode rather than simply using the average load current.

Depending on the application, consider:

• Average current
• Peak current
• RMS current
• Surge current
• Duty cycle
• Ambient temperature

The manufacturer's thermal conditions must also be considered because the current rating is not independent of temperature.

Replacing a Schottky Diode

When replacing a Schottky diode, compare the original and replacement datasheets carefully.

Check:

• Schottky technology/type
• Reverse-voltage rating
• Forward-current rating
• Forward voltage
• Reverse leakage
• Thermal characteristics
• Package
• Pin configuration
• Polarity

For a switching converter, also compare the diode's behavior at the actual switching frequency and operating current.

Common Selection Mistakes

• Choosing only by forward-current rating
• Ignoring reverse-voltage rating
• Ignoring reverse leakage
• Ignoring temperature effects
• Ignoring power dissipation
• Using a generic silicon diode instead of a required Schottky diode
• Ignoring package configuration
• Using a high-current diode without providing adequate cooling

Quick Selection Checklist

• ✔ Identify the application
• ✔ Determine maximum reverse voltage
• ✔ Determine average and peak current
• ✔ Check forward voltage at operating current
• ✔ Check reverse leakage
• ✔ Check switching requirements
• ✔ Check temperature range
• ✔ Calculate approximate power dissipation
• ✔ Check package and pin configuration
• ✔ Verify the manufacturer's datasheet

Key Points

• Schottky diodes use a metal-semiconductor junction.
• They generally have a lower forward voltage than conventional silicon PN diodes.
• They provide very fast switching with very low charge-storage effects.
• Reverse leakage is generally higher and can increase significantly with temperature.
• Many conventional Schottky devices have lower reverse-voltage ratings than high-voltage PN rectifiers.
• They are widely used in SMPS, DC-DC converters, low-voltage rectifiers, RF detectors, and protection circuits.
• Always check the complete datasheet rather than selecting a Schottky diode by one specification alone.