# MMST5551

**hongjiacheng** · Bipolar (BJT) · SOT-323

MMST5551 from hongjiacheng, in a SOT-323. 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 of the NPN transistor; the function diagram shows pin 1 as the base, with emitter-base breakdown V(BR)EBO of 6.0V min and VEBO max of 6.0V. |
| 2 | E | passive | Emitter of the NPN transistor; the function diagram shows pin 2 at the arrow terminal, with VEBO max of 6.0V. |
| 3 | C | passive | Collector of the NPN transistor; the datasheet rates it for VCBO 180V, VCEO 160V and IC 0.6A. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | hongjiacheng |
| Package | SOT-323 |
| 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 |  |  | 180 | V |  | 1 |
| Collector-Emitter Voltage | VCEO |  |  | 160 | V |  | 1 |
| Emitter-Base Voltage | VEBO |  |  | 6 | V |  | 1 |
| Collector Current | IC |  |  | 0.6 | A |  | 1 |
| Collector Power Dissipation | PC |  |  | 200 | mW |  | 1 |
| Storage temperature | Tstg | -55 |  | 150 | ℃ |  | 1 |
| Junction temperature | Tj | -55 |  | 150 | ℃ |  | 1 |
| Collector-Base Breakdown Voltage | V(BR)CBO | 180 |  |  | V | IC=100μA, IE=0 | 1 |
| Collector-Emitter Breakdown Voltage | V(BR)CEO | 160 |  |  | V | IC=1mA, IB=0 | 1 |
| Emitter-Base Breakdown Voltage | V(BR)EBO | 6 |  |  | V | IE=100μA, IC=0 | 1 |
| Collector-Emitter cut-off current | ICBO |  |  | 50 | nA | VCE=120V, IB=0 | 1 |
| Emitter-Base cut-off current | IEBO |  |  | 50 | nA | VEB=4.0V, IC=0 | 1 |
| DC Current Gain hFE(1) | hFE(1) | 80 |  |  |  | IC=1.0mA VCE=5.0V | 1 |
| DC Current Gain hFE(2) | hFE(2) | 80 |  | 300 |  | IC=10mA VCE=5.0V | 1 |
| DC Current Gain hFE(3) | hFE(3) | 30 |  |  |  | IC=50mA VCE=5.0V | 1 |
| Collector-Emitter Saturation Voltage | VCE(sat) |  |  | 0.15 | V | IC=10mA IB=1mA | 1 |
| Base-Emitter Saturation Voltage | VBE(sat) |  |  | 1 | V | IC=10mA IB=1mA | 1 |
| Collector output capacitance | Cob |  |  | 6 | pF | VCB=10V,IE=0,f=1MHz | 1 |
| Transition frequency | fT | 100 |  | 300 | MHz | IC=10mA, VCE=10V，f=100MHz | 3 |
| Typical Thermal Resistance, junction to ambient | RθJ-A |  | 625 |  | ℃/W |  | 1 |

## CAD (KiCad official)

- Symbol: `MMST5551`
- Footprint: `Package_TO_SOT_SMD:SOT-323_SC-70`
- 3D model: SOT-323 (KiCad packages3D, STEP)
- 3D model files: `mmst5551-etched.step` / `mmst5551-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `mmst5551.step` / `mmst5551.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [hongjiacheng datasheet](https://jlcpcb.com/api/file/downloadByFileSystemAccessId/8604448564001193984) (3 pp, sha256 `1368b3f7c24ca204`, retrieved 2026-10-09, tier: lcsc)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-sonnet-5-5` (text+vision), consensus `claude-opus-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/mmst5551-datasheet.pdf)