What Is a SOT-23 Switching Diode?

SOT-23 is a package, not a specification: the same 100 V, 4 ns switching silicon ships in six outlines. What the outline decides, and what it does not.

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SOT-23 is a package, not a specification. The same 100 V, 4 ns switching silicon appears in SOT-23, SOT-323, SOT-416, SOD-323, SOD-523 and even a leadless SOD-882 body, and what the outline changes is board area, thermal path, pin count and the configuration options you can get — not how fast the diode switches.

Last updated: October 11, 2026

Key Takeaways

The switching numbers belong to the die: the BAV99 series quotes a 4 ns reverse recovery time under a stated test condition, with junction capacitance at 1.5 pF or less.
SOT-23 buys three leads, which is what makes the dual-diode configurations possible — series, common anode or common cathode, depending on which family you order.
Reverse voltage in this class is typically 100 V, which places the part in signal and control paths rather than in mains rectification.
Marking codes matter at assembly and rework: a SOT-23 with no readable code is a part you cannot identify after the reel is gone.
Automotive programmes can use the same families: the BAS16 and BAV99 series are AEC-Q101 qualified.

What the Outline Does, and Does Not, Decide

A SOT-23 switching diode is a small-signal diode in the three-lead SOT-23 (TO-236AB) surface-mount outline. It is used where a signal or a low-current path has to be steered, clamped or blocked quickly, and it is chosen over a larger rectifier for exactly that reason.

The Nexperia BAV99 series is a useful reference: a high-speed switching diode family with a reverse recovery time of 4 ns or less when switched from 10 mA forward to 10 mA reverse through a 100 Ω load and measured at 1 mA, junction capacitance of 1.5 pF or less, reverse voltage of 100 V, reverse current of 0.5 µA or less at 80 V, and AEC-Q101 qualification — offered in SOT23 as a dual-series device, in SOT363 as a quadruple (two series pairs), and in SOT323 as a dual-series part in a smaller outline. The BAS16 series covers the same electrical class across a wider set of outlines, from SOT23 down to the leadless SOD882.

Parameter	Value in this class	Why it decides the design
Reverse recovery time t_rr	4 ns or less (10 mA → 10 mA, R_L = 100 Ω, read at 1 mA)	Sets how much current keeps flowing after the voltage reverses
Junction capacitance C_d	1.5 pF or less	Loads the node continuously, not only during switching
Reverse voltage V_R	100 V	Places the part in signal and control paths
Reverse current I_R	0.5 µA or less at V_R = 80 V	The standby figure on a high-impedance node
Configurations in SOT-23	Dual series; related families offer single, common anode and common cathode	Determines whether the package fits the circuit at all
Qualification	AEC-Q101 qualified across the series	Automotive programmes use the same family

Configurations: Why Three Leads Matter

Three leads are what let the package hold two diodes with a shared node, and the shared node is the whole point. The small-signal Schottky families show the pattern most clearly: the ST BAT54 device summary lists a single diode, a common-anode version (BAT54A), a common-cathode version (BAT54C) and a series version (BAT54S) built on the same 40 V, 300 mA die. Switching-diode families follow the same logic, which is why a designation suffix rather than the footprint tells you what you are buying.

That is the practical consequence for a schematic and a BOM. Two diodes in one SOT-23 save a placement and a footprint, but only if the shared node is where the circuit needs it: a common-anode part cannot be rotated into a common-cathode position, and a series pair is not interchangeable with either. Check the configuration before the layout, not after.

Reading the Part You Actually Have

Once the reel is off the machine, the marking code is the only identification left. SOT-23 devices carry short codes rather than full type numbers — the Nexperia BAS16 is marked with a two-character code — so a marking table in the datasheet is a production document, not an appendix. It is what lets a rework station confirm that the part it is about to fit is the one the BOM specifies, and it is the first thing to check when a board behaves differently from its predecessor.

Two boundary conditions go with the class. Reverse voltage: 100 V suits signal and low-voltage rails, and a design that needs to block mains or a high-voltage DC bus belongs to a rectifier family instead. Thermal: the current this outline can carry continuously is limited by the copper it sits on, so a part used at its rated current in a warm enclosure is a derating calculation rather than a datasheet lookup.

FAQ

What is the main job of a SOT-23 switching diode?

Fast, low-current steering, clamping and blocking on a signal or control path — the tasks where the diode has to switch off quickly and where a rectifier’s recovery time would be a liability.

Is a SOT-23 switching diode the same as a rectifier diode?

No. A rectifier is optimised for forward current and blocking voltage; a switching diode is optimised for recovery time and low capacitance, with a much lower current rating. They sit in different parts of a circuit.

Why is reverse recovery time important?

Because the diode keeps conducting briefly after the voltage reverses. In a fast circuit that current pulse flows through the surrounding loop, where it can slow an edge, cause ringing, or add to the loss in the device driving the node.

Can SOT-23 switching diodes be used in automotive designs?

The families used here are AEC-Q101 qualified, so an automotive programme can select from the same series rather than switching families. The qualification report applies to the exact part and package variant.

What should I check before replacing one part with another?

The configuration and pinout, the reverse recovery time at your switching conditions, the junction capacitance, the reverse voltage class, and the marking code — so that the substitute is identifiable on the board.

Official Resources

References

Nexperia, BAV99 series — High-speed switching diodes, Rev. 8 — source of the 4 ns reverse recovery time with its test conditions, the 1.5 pF maximum junction capacitance, 100 V reverse voltage, 0.5 µA maximum reverse current at 80 V, and the SOT23 dual-series, SOT363 quadruple and SOT323 dual-series package options with AEC-Q101 qualification. assets.nexperia.com — BAV99 series datasheet (PDF)
Nexperia, BAS16 series — High-speed switching diodes, Rev. 6 — source of the wider outline list for the same class, including the marking information. assets.nexperia.com — BAS16 series datasheet (PDF)
STMicroelectronics, BAT54 — Small signal Schottky diodes, DocID5505 Rev 12 — source of the single, common-anode, common-cathode and series configuration families used to illustrate why three leads matter. st.com — BAT54 datasheet (PDF)

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