# 2SD1781

**Changjing** · Bipolar (BJT) · SOT-23

2SD1781 from Changjing, in a SOT-23. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | BASE | input | Base terminal of the 2SD1781 NPN transistor; the datasheet's maximum rated emitter-base voltage VEBO is 5 V. |
| 2 | EMITTER | passive | Emitter terminal of the 2SD1781 NPN transistor; the same 5 V maximum emitter-base voltage rating (VEBO) applies across the emitter and base. |
| 3 | COLLECTOR | passive | Collector terminal of the 2SD1781 NPN transistor; the datasheet's maximum ratings are VCBO 40 V, VCEO 32 V and collector current IC 800 mA. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | Changjing |
| Package | SOT-23 |
| Category | Transistors/Thyristors |
| Pins | 3 |

## Electrical characteristics

Limits as printed in the datasheet (page.json `metadata.characteristics` carries them as data).

| Parameter | Symbol | Min | Typ | Max | Unit | Conditions | Page |
|---|---|---|---|---|---|---|---|
| Collector-base breakdown voltage | V(BR)CBO | 40 |  |  | V | IC=50μA,IE=0 | 1 |
| Collector-emitter breakdown voltage | V(BR)CEO | 32 |  |  | V | IC=1mA,IB=0 | 1 |
| Emitter-base breakdown voltage | V(BR)EBO | 5 |  |  | V | IE=50μA,IC=0 | 1 |
| Collector cut-off current | ICBO |  |  | 0.5 | μA | VCB=20V,IE=0 | 1 |
| Emitter cut-off current | IEBO |  |  | 0.5 | μA | VEB=4V,IC=0 | 1 |
| DC current gain | hFE(1) | 120 |  | 390 |  | VCE=3V,IC=100mA | 1 |
| Collector-emitter saturation voltage | VCE(sat) |  |  | 0.4 | V | IC=500mA,IB=50mA | 1 |
| Transition frequency | fT | 150 |  |  | MHz | VCE=5V,IC=50mA,f=100MHz | 1 |
| Collector output capacitance | Cob |  |  | 10 | pF | VCB=10V,IE=0,f=1MHz | 1 |
| Collector-Base Voltage | VCBO |  |  | 40 | V |  | 1 |
| Collector-Emitter Voltage | VCEO |  |  | 32 | V |  | 1 |
| Emitter-Base Voltage | VEBO |  |  | 5 | V |  | 1 |
| Collector Current | IC |  |  | 800 | mA |  | 1 |
| Collector Power Dissipation | PC |  |  | 200 | mW |  | 1 |
| Operation Junction and Storage Temperature Range | TJ,Tstg | -55 |  | 150 | ℃ |  | 1 |
| Thermal Resistance From Junction To Ambient | RΘJA |  |  | 625 | ℃/W |  | 1 |

## CAD (KiCad official)

- Symbol: `2SD1781`
- Footprint: `Package_TO_SOT_SMD:SOT-23`
- 3D model: SOT-23 (KiCad packages3D, STEP)
- 3D model files: `2sd1781-etched.step` / `2sd1781-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `2sd1781.step` / `2sd1781.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [Changjing datasheet](https://jlcpcb.com/api/file/downloadByFileSystemAccessId/8602943873798979584) (4 pp, sha256 `b0d5a3f7653c931b`, retrieved 2026-10-18, tier: lcsc)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-haiku-5-5` (text), consensus `claude-sonnet-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/2sd1781-datasheet.pdf)