How to Choose the Right Schottky Diode for Your Circuit Design

Understand the key decisions and options when selecting a Schottky diode for your circuit design - from my experience I explain the options, advantages and disadvantages that need to be considered.

Home » Electronic components » this page

Diode Tutorial Includes:
Diode types Diode specs & ratings PN junction diode Fast recovery diode LED PIN diode Schottky barrier diode SiC diode Solar cell / photovoltaic diode Transient voltage suppressor diode Varactor / varicap Zener diode

Diode component data: PN junction diode data Schottky diode data Silicon carbide, SiC Schottky diode data

When designing any circuit, there are many decisions to make and these often require skill and expertise to gain the right balance between several factors.

Choosing the right Schottky barrier diode is a classic example of balancing interdependent trade-offs.

This page focusses on the traditional silicon Schottky diodes, but of course, Silicon Carbide Schottky's are also available and are the ideal choice for many applications.

For design engineers working on high-frequency power supplies, reverse polarity protection, or low-voltage power OR-ing rails, the Schottky diode is an indispensable tool. Its distinct lack of a standard p-n junction gives it two legendary properties: an exceptionally low forward voltage drop (V_F) and near-zero reverse recovery time (t_rr).

but there are disadvantages to using these diodes as well. Silicon Schottky diodes have a high reverse leakage, and this is even worse at high temperatures.

Another disadvantage is that their maximum reverse voltage blocking capability (V_RRM) tops out around 200V for the highest voltage diodes and for many it is very much less.

1. The Physics Brief: Why It Matters to the Circuit

To select the right component, we must first look at how a Schottky diode behaves under the hood. Traditional rectifiers rely on a p-n semiconductor junction where minority charge carriers must recombine when switching from a forward-biased state to a reverse-biased state. This recombination takes time, manifesting as a reverse recovery current spike (I_RM) and a corresponding time delay (t_rr).

A Schottky diode replaces the p-type element of the junction with a metal contact (typically molybdenum, platinum, chromium, or tungsten) bonded to an n-type silicon substrate.

Deposited metal Schottky diode structure and technology — Deposited metal Schottky diode structure
*Note, real diodes typically have a more complicated structure to improve performance and reduce breakdown*

As a result of the fact that the current is carried almost entirely by majority carriers, i.e. electrons in the conduction band, there is virtually no stored minority carrier charge.

When the voltage flips, the current shuts off near-instantaneously. The "switching loss" seen in a silicon Schottky datasheet isn't caused by carrier recombination; it is almost entirely the result of charging and discharging the device's parasitic junction capacitance (C_J).

2. Core electrical parameters demystified

When looking at a datasheet for a classic part like an MBR340, SS14, or a high-current trench Schottky, it is really important to look at how parameters shift under real-world operating conditions.

Maximum Repetitive Reverse Voltage (V_RRM)

This is the absolute maximum peak voltage the diode can block in its off-state.

The Engineering Rule: Never run a silicon Schottky right at its V_RRM limit. High-frequency circuits inherently suffer from inductive voltage spikes during switching transitions.
he Recommendation: Often design recommendations suggest a safety margin of at least 20% to 30% above your maximum steady-state DC rail. I personally prefer to run things with a 40% margin, i.e. at a maximum of 60% of the design maximum ratings. If you are rectifying a 24V rail that sees transient spikes up to 32V, a 40V or 45V rated diode (V_RRM) is the bare minimum; a 60V device is significantly much safer, and there is often little cost difference.

Forward Voltage Drop (V_F)

The headline feature of the Schottky is a low V_F, typically between 0.2V and 0.5V, compared to 0.7V to 1.1V for standard silicon p-n diodes. (Although the turn on voltage is typically 0.2V for Schottky diodes and 0.6 to 0.7V for standard silicon diodes, when current passes through the overall voltage drop is actually higher).

The Nuance: V_F is composed of two distinct parts: the ideal barrier voltage and the internal series resistance (R_D) of the silicon substrate multiplied by the forward current (I_F). At low currents, the barrier voltage dominates. At high currents, the ohmic voltage drop across R_D takes over, causing the V_F curve to steepen significantly.
Temperature Dependency: Crucially, V_F features a negative temperature coefficient. As the junction temperature (T_J) increases, V_F drops. While this slightly improves conduction efficiency at high loads, it directly worsens the next parameter.

Reverse Leakage Current (I_R)

The reverse leakage current is one of the major disadvantages of Schottky diodes and in some instances it can mean that silicon Schottky diodes are not able to be used.

While a standard p-n diode might leak a few nanoamps or microamps under reverse bias, a silicon Schottky can easily leak hundreds of microamps at room temperature (25°C).

The Temperature Trap: I_R scales exponentially with temperature. A Schottky leaking 10µA at room temperature can easily leak 10 mA to 50 mA when running hot at 125°C. This leakage represents a major source of standby power dissipation and introduces the real danger of thermal runaway.

Average Rectified Forward Current (I_F(AV)) and Surge Current (I_FSM)

I_F(AV): The maximum average current the diode can sustain continuously over a complete cycle, usually specified under a specific thermal environment (e.g., a specific PCB copper pad area or lead temperature).
I_FSM: The non-repetitive peak surge current the device can handle for a brief window (typically a single half-sine wave pulse at 50Hz or 60Hz). This is critical for circuits charging large input bulk capacitors at startup, where inrush currents can be orders of magnitude higher than nominal operating currents.

1N5822 diodes — A pair of 1N5822 Schottky diodes

7. The Design Engineer's Selection Checklist

When selecting a silicon Schottky diode , here is a streamlined approach that can be adopted.

Verify V_RRM: Ensure a minimum of a 30% margin over the absolute highest voltage spike expected on the node. I would recommend more if possible to accommodate any transients that might appear.
Check V_F at Peak Operating Current: Do not look only at the headline typical value; look at the I_F vs V_F curve at your maximum operating temperature.
Calculate High-Temperature Leakage: Check the I_R curve at 100^\circ\text{C}+. If the leakage power dissipation exceeds a few milliwatts, re-evaluate your thermal layout or consider a trench device.
Match the Package to the Power: Compact surface mount options like SOD-123 or SMA are excellent for signal clamping and low currents, but high-current switchers need DPAK, D2PAK, or through-hole TO-220 packages with ample copper ground planes acting as heat sinks.
Account for Parasitic Capacitance (C_J): For high-frequency layouts, verify that the energy stored in C_J won't create unacceptable switching losses or introduce unexpected EMI ringing into your circuit.