A Schottky diode is a semiconductor diode formed by a metal-semiconductor junction rather than a p-n junction, resulting in a lower forward voltage drop (typically 0.15 V to 0.45 V) and very fast switching due to the absence of minority carrier storage.
In practice
In embedded power circuits, Schottky diodes are commonly used for reverse-polarity protection, catch/freewheeling diodes on inductive loads, and diode-OR power path circuits. Their low forward drop makes them preferable to standard silicon p-n diodes (which drop roughly 0.6 V to 0.7 V) wherever supply efficiency or headroom matters, such as in battery-powered designs.
In switching power supplies, Schottky diodes are a frequent choice for the rectifier or synchronous-rectifier bypass position because their lack of a minority carrier reverse-recovery time reduces switching losses at high frequencies. Parts like the 1N5817-1N5819 series (1 A) and B340 (3 A) appear in many reference designs for this reason. However, Schottky diodes typically have higher reverse leakage current than p-n diodes, and that leakage rises significantly with temperature, which can become a relevant loss in high-ambient or self-heating environments.
Schottky diodes are also widely used as clamping and protection devices on logic and MCU I/O lines, and as the body-diode bypass in discrete FET gate-drive circuits. The blog post "Modeling Gate Drive Diodes" discusses nuances of diode selection in gate-drive paths. "Byte and Switch (Part 2)" and "Hot Fun in the Silicon: Thermal Testing with Power Semiconductors" are relevant when evaluating the thermal behavior of these devices in real circuit conditions.
One practical pitfall is assuming a Schottky diode's forward drop is always low: at high currents the resistive component of the junction can push the drop well above the low-current datasheet value. At the other extreme, the reverse leakage at elevated temperature can be significant enough to cause thermal runaway in some configurations -- a concern covered in depth in "Voltage Drops Are Falling on My Head: Operating Points, Linearization, Temperature Coefficients, and Thermal Runaway".
Frequently asked
Why choose a Schottky diode over a standard silicon diode in a power circuit?
The main reasons are lower forward voltage drop (often 0.2 V to 0.4 V vs. 0.6 V to 0.7 V for a p-n
diode at similar currents) and faster switching with no reverse-recovery charge. Both traits reduce losses in rectifiers, freewheeling paths, and power-path OR circuits, which is particularly valuable in low-voltage or battery-powered designs.
What is reverse-recovery time, and why does it matter for Schottky diodes?
Reverse-recovery time is the interval a p-n
diode conducts in reverse while stored minority carriers are swept out. Schottky diodes use a metal-semiconductor junction with majority-carrier conduction only, so they have negligible minority carrier storage and switch off much faster. This makes them suitable for high-frequency switching applications where a slow-recovery diode would cause significant switching losses or voltage spikes.
What are the main drawbacks of Schottky diodes compared to p-n junction diodes?
Schottky
diodes generally have lower reverse breakdown voltages (many common parts are rated 20 V to 60 V, though higher-voltage parts exist), and they exhibit significantly higher reverse leakage current that increases sharply with temperature. In high-temperature environments this leakage can become a non-trivial loss and, in worst-case situations, can contribute to thermal runaway. They also tend to cost slightly more than equivalent p-n rectifier diodes.
Can I use a Schottky diode for reverse-polarity protection on an MCU power rail?
Yes, a series Schottky
diode is a simple and common approach. The reduced forward drop compared to a standard diode preserves more usable headroom. For very low-dropout designs, a PMOS FET controlled to act as an ideal diode is often preferred, since it can be driven to a much lower drop. The tradeoff is circuit complexity. Either way, ensure the diode's current and voltage ratings cover the worst-case supply conditions.
How does temperature affect a Schottky diode's forward drop and leakage?
Like p-n
diodes, the forward voltage drop of a Schottky diode decreases with rising temperature -- roughly -1 mV/°C to -2 mV/°C depending on the device and operating point. Reverse leakage, however, increases substantially with temperature, and for some Schottky parts it can roughly double for every 10°C rise. In designs where the diode runs warm, it is worth checking datasheet curves at the actual operating temperature rather than relying only on room-temperature values. The post 'Voltage Drops Are Falling on My Head' discusses this temperature coefficient behavior in detail.
Differentiators vs similar concepts
Schottky
diodes are often compared to standard silicon p-n rectifier diodes (e.g., 1N4001 series) and to
Zener diodes. Unlike p-n rectifiers, Schottky diodes use a metal-semiconductor junction, giving them lower forward drop and negligible reverse-recovery charge, at the cost of higher leakage and typically lower reverse voltage ratings. Unlike Zener diodes, which are designed to conduct in reverse at a controlled breakdown voltage for regulation or clamping, Schottky diodes are not normally operated in reverse breakdown. Schottky diodes are also distinct from PIN diodes, which are optimized for
RF switching and photodetection rather than rectification or clamping.
