What Is a Small Signal Schottky Barrier Diode?

A small-signal Schottky diode trades leakage for a 410 mV forward drop. What three real parts specify, and the calculation that decides whether it fits.

Request a Quote

What Is a Small Signal Schottky Barrier Diode?

A small-signal Schottky barrier diode is chosen for a forward drop measured in hundreds of millivolts, and paid for in reverse leakage measured in tens of microamps. One real device makes the trade concrete: Nexperia’s PMEG2005EPK drops 410 mV maximum at 500 mA, recovers in 3 ns — and specifies up to 130 µA of reverse leakage at just 10 V. Whether that is a bargain or a problem depends entirely on the node it sits on.

Last updated: October 11, 2026

Key Takeaways

The barrier is a metal-semiconductor junction, so the diode has no minority-carrier storage to clear — recovery is in the nanosecond range rather than the hundreds of nanoseconds a p-n device can need.
Barrier height is a design choice with two ends: lowering it reduces the forward drop and raises reverse leakage. The datasheet always shows both.
Reverse voltage is the other limit. Small-signal Schottky parts in these families are rated at 20 V, 30 V or 40 V, well below a p-n switching diode.
Leakage at temperature is the number that surprises designs: in the BAT54 family the maximum rises from 1 µA at 25 °C to 100 µA at a 100 °C junction.
Package choice follows the current: a leadless outline for density, a flat-lead power outline when the same function has to carry more.

Three Real Parts, and What Each One Costs

Reading three datasheets side by side shows the trade better than any summary. All three are small-signal Schottky rectifiers; the differences are the barrier, the package and the leakage you accept in exchange for the forward drop.

Parameter	PMEG2005EPK	PMEG4005EJ	BAT54 (ST)
Reverse voltage	20 V	40 V	40 V
Current	0.5 A average	0.5 A average; 7 A repetitive peak (1 ms, δ ≤ 0.25); 10 A non-repetitive (8 ms square)	300 mA continuous; 1.25 A non-repetitive (10 ms sinusoidal)
Forward voltage	360 mV typ, 410 mV max at 500 mA	420 mV typ, 470 mV max at 500 mA	240 mV at 0.1 mA; 400 mV at 10 mA; 900 mV at 100 mA (max)
Reverse leakage	30 µA typ, 130 µA max at 10 V	Per the datasheet curves at the rated voltage	1 µA max at 25 °C; 100 µA max at 100 °C (V_R = 30 V)
Recovery / capacitance	3 ns typical recovery	Schottky behaviour; no minority-carrier recovery	7 pF typical, 10 pF max; 5 ns reverse recovery
Package	DFN1608D-2 (SOD1608), 0.37 mm high	SC-90 (SOD323F), 1.7 × 1.25 × 0.7 mm	SO123, SOD323, SOD523, SOT-23, SOT-323
Thermal path	Ceramic-PCB mounting condition for the rated current	Flat-lead body; 360 mW or 830 mW dissipation depending on the pad	500 °C/W junction-to-ambient in SOT-23; 550 in SOT-323/SOD323; 600 in SOD-523

Two rows in that table are the whole argument. Forward drop falls as the barrier is lowered, and leakage rises with it — the 20 V part has the lowest drop and the highest leakage of the three. Reverse voltage is the second: the same technology that makes the diode fast also caps how much voltage it can block, which is why this class stops well short of the 100 V a p-n switching diode offers.

The Calculation That Decides Whether It Fits

Compare the two losses on the same node and the choice usually resolves itself.

Conduction: at 100 mA, the BAT54 family specifies 900 mV maximum, so the diode dissipates 90 mW. In SOT-23, with the datasheet’s 500 °C/W junction-to-ambient figure, that is a 45 °C rise above ambient.
Leakage: the same part is specified at 1 µA maximum at 25 °C and 100 µA maximum at 100 °C. At 30 V that hot figure is 3 mW of continuous loss.
The comparison to make: 3 mW of leakage against 90 mW of conduction loss. On a conducting path the leakage is a rounding error; on a blocking path with no load current, it is the only loss there is.

That is a model assembled from the datasheet’s own maximums with stated assumptions, not a measurement, and the conclusion is the selection rule for the class: small-signal Schottky diodes belong where current flows in the forward direction for a meaningful fraction of the time, and a p-n device belongs where the diode is expected to block and stay quiet — particularly at temperature.

Where They Belong

Low-voltage rectification, reverse-polarity and reverse-current blocking, freewheeling in small converters, and OR-ing of low-voltage rails are the natural duties. The package follows the current and the density: the PMEG2005EPK’s leadless 0.37 mm body is for the smallest boards, while the flat-lead power outline (the CFP15 package used by the 3 A PMEG030V030EPD, qualified to AEC-Q101) is the step up when the same function must carry more current in a slightly thicker part.

Two boundaries are worth stating before a design freezes. High reverse voltage belongs to a different family, and so does any requirement for microamp-level leakage at a high junction temperature. Where either applies, the honest answer is a p-n or wide-bandgap device rather than a Schottky with a lower forward drop.

FAQ

What is the purpose of a Schottky barrier diode?

To conduct with a lower forward drop and switch faster than a p-n diode, because its junction stores no minority carriers. That makes it useful for low-voltage rectification, blocking and freewheeling — with the trade that it leaks more and blocks less voltage.

What is a small signal diode?

It is a diode intended for low currents and signal-level duties rather than for power conversion. In this class the current rating is typically a few hundred milliamps, and the important specifications are the forward drop at that current, the leakage, and the capacitance.

Why does a lower forward drop mean more leakage?

Because both follow from the barrier height. A lower barrier lets carriers through more easily in the forward direction and also in reverse, so a part specified at 410 mV maximum at 500 mA can be specified at 130 µA maximum of leakage.

What reverse voltage can a small-signal Schottky block?

In these families, 20 V, 30 V or 40 V. That ceiling is inherent to the technology at this size, and it is why 100 V signal duties are handled by p-n switching diodes instead.

Where does leakage actually matter?

On nodes that spend their time blocking: a battery-backed hold-up path, a sensing input, or a rail that must not bleed. On a path that conducts most of the time, the conduction loss dominates the comparison.

Official Resources

References

Nexperia, PMEG2005EPK — 20 V, 0.5 A low V_F Schottky barrier rectifier — source of the 410 mV maximum forward voltage at 500 mA, 130 µA maximum leakage at 10 V, 3 ns recovery, and the DFN1608D-2 outline 0.37 mm high with its ceramic-PCB current condition. assets.nexperia.com — PMEG2005EPK datasheet (PDF)
Nexperia, PMEG4005EJ — 40 V, 0.5 A very low V_F MEGA Schottky barrier rectifier — source of the 470 mV maximum forward voltage, the 7 A repetitive peak and 10 A non-repetitive ratings, the SC-90 (SOD323F) dimensions and the 360 mW / 830 mW dissipation figures. assets.nexperia.com — PMEG4005EJ datasheet (PDF)
STMicroelectronics, BAT54 — Small signal Schottky diodes, DocID5505 Rev 12 — source of the 40 V / 300 mA ratings, the forward voltage at five currents, the leakage at 25 °C and 100 °C, the 7 pF capacitance, 5 ns recovery and the 500 / 550 / 600 °C/W thermal resistances by package. st.com — BAT54 datasheet (PDF)
Nexperia, PMEG030V030EPD — 30 V, 3 A low V_F MEGA Schottky barrier rectifier — the flat-lead power-outline step-up referenced in the package discussion, with its AEC-Q101 qualification. assets.nexperia.com — PMEG030V030EPD datasheet (PDF)

Continue through this engineering topic

For the complete selection, design, verification, and troubleshooting path, explore the Zener and Signal Diode Hub.