# BF420

**Changjing** · Bipolar (BJT) · TO-92

BF420 from Changjing, in a TO-92. 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 | EMITTER | passive | Emitter terminal of the NPN transistor, with a maximum emitter-base voltage VEBO of 5 V and a maximum continuous collector current of 100 mA stated for the device. |
| 2 | COLLECTOR | passive | Collector terminal of the NPN transistor, rated for a collector-emitter voltage VCEO of 300 V (BF420) or 250 V (BF422) and a continuous collector current of 100 mA. |
| 3 | BASE | passive | Base terminal of the NPN transistor; the datasheet gives no base-specific rating beyond the device maximum ratings. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | Changjing |
| Package | TO-92 |
| 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 Voltage | VCBO |  |  | 300 | V |  | 1 |
| Collector-Emitter Voltage | VCEO |  |  | 300 | V |  | 1 |
| Emitter-Base Voltage | VEBO |  |  | 5 | V |  | 1 |
| Collector Current - Continuous | IC |  |  | 100 | mA |  | 1 |
| Operation Junction and Storage Temperature Range | TJ,Tstg | -55 |  | 150 | ℃ |  | 1 |
| Thermal resistance from junction to ambient | Rthja |  |  | 151 | ℃/W |  | 1 |
| Collector-base breakdown voltage | V(BR)CBO | 300 |  |  | V | IC=100μA, IE=0 | 2 |
| Collector-emitter breakdown voltage | V(BR)CEO | 300 |  |  | V | IC=1mA, IB=0 | 2 |
| Emitter-base breakdown voltage | V(BR)EBO | 5 |  |  | V | IE=100μA, IC=0 | 2 |
| Collector cut-off current | ICBO |  |  | 0.01 | μA | VCB=200V, IE=0 | 2 |
| Emitter cut-off current | IEBO |  |  | 0.05 | μA | VEB=5V, IC=0 | 2 |
| DC current gain | hFE | 50 |  |  |  | VCE=20V, IC=25mA | 2 |
| Collector-emitter saturation voltage | VCE(sat) |  |  | 0.6 | V | IC=30mA, IB=5mA | 2 |
| Transition frequency | fT | 60 |  |  | MHz | VCE=10V, IC=10mA, f=100MHz | 2 |
| Feedback capacitance | Cre |  |  | 1.6 | pF | VCE=30V, IC=0, f=1MHz | 2 |

## CAD (KiCad official)

- Symbol: `BF420`
- Footprint: `Package_TO_SOT_THT:TO-92_Inline`
- 3D model: TO-92 (KiCad packages3D, STEP)
- 3D model files: `bf420-etched.step` / `bf420-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `bf420.step` / `bf420.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/8590920203603955712) (4 pp, sha256 `59caae688fbf914f`, retrieved 2026-10-17, 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/bf420-datasheet.pdf)