# TIP121

**STMicroelectronics** · Darlington Transistors · TO-220-3

TIP121 from STMicroelectronics, in a TO-220-3. 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 | B | input | Base terminal of the monolithic NPN Darlington, with internal R1 = 7 kΩ and R2 = 70 Ω, and base current limited to 0.12 A (absolute maximum). |
| 2 | C | passive | Collector terminal, electrically connected to the metal tab; rated 80 V VCEO and 80 V VCBO for TIP121, 5 A continuous collector current and 8 A peak (ICM). |
| 3 | E | passive | Emitter terminal of the NPN Darlington; the emitter-base voltage is rated at 5 V maximum (VEBO). |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | STMicroelectronics |
| Package | TO-220-3 |
| Category | Transistors/Thyristors |
| Pins | 3 |

## CAD (KiCad official)

- Symbol: `TIP121`
- Footprint: `Package_TO_SOT_THT:TO-220-3_Vertical`
- 3D model: TO-220-3 (KiCad packages3D, STEP)
- 3D model files: `tip121-etched.step` / `tip121-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `tip121.step` / `tip121.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [STMicroelectronics datasheet](https://jlcpcb.com/api/file/downloadByFileSystemAccessId/8590224496398397440) (13 pp, sha256 `e726b0e3ab76c110`, retrieved 2026-10-08, 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/tip121-datasheet.pdf)