Two small Schottky diodes connected in series inside one SOT-23, with the shared cathode/anode node brought out on pin 3. The low forward drop (about 0.32 V) and fast recovery of a Schottky, in a tiny surface-mount package, make the BAT54S the default for signal steering and OR-ing two sources, level shifting, small-signal rectification, and clamping a node between two rails (tie the outer pins to the rails, the signal to the center). It blocks 30 V and handles 200 mA. The related BAT54 (single), BAT54A (common anode), and BAT54C (common cathode) cover the other configurations.

Pinout

Pin	Name	Type	Function
1	A1	passive	Anode of diode D1. Forward-biased current flows from pin 1 (A1) through D1 to pin 3 (K1/A2, the internal series node).
2	K2	passive	Cathode of diode D2. Forward current from pin 3 (K1/A2 series node) exits through D2 to pin 2.
3	K1_A2	passive	Series junction node: cathode of D1 connected internally to anode of D2. This is the shared middle pin of the BAT54S series-diode configuration.

Key specifications

Parameter	Value
Type	Series dual Schottky diode
Configuration	2 diodes in series (common node = pin 3)
Reverse voltage (VRRM)	30 V
Forward current (IF)	200 mA
Forward voltage (VF)	~0.32 V at 10 mA
Recovery	fast (Schottky)
Pinout	1=A1, 2=K2, 3=common (K1/A2)
Package	SOT-23

Ordering variants

BAT54S-7-F (SOT-23)
BAT54S (SOT-23, tape & reel)

CAD (KiCad official)

Symbol: Diode:BAT54S
Footprint: Package_TO_SOT_SMD:SOT-23
3D model: SOT-23 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Diodes Incorporated datasheet (5 pp, sha256 50b04e4e17bcf5db, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF