# BD438

**STMicroelectronics** · Bipolar (BJT) · TO-126-3

BD438 from STMicroelectronics, in a TO-126-3. 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 | Base | input | Control input terminal with maximum base current of 1 A |
| 2 | Collector | output | Collector terminal with maximum collector current of 4 A and collector-emitter voltage of 45 V |
| 3 | Emitter | output | Emitter terminal with maximum emitter-base voltage of 5 V |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | STMicroelectronics |
| Package | TO-126-3 |
| 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 |  |  | 45 | V | IE = 0; PNP BD438 column (datasheet note: PNP voltage/current values are negative) | 1 |
| Collector-Emitter Voltage | VCES |  |  | 45 | V | VBE = 0; PNP BD438 column (datasheet note: PNP voltage/current values are negative) | 1 |
| Emitter-Base Voltage | VEBO |  |  | 5 | V | IC = 0 | 1 |
| Collector Current | IC |  |  | 4 | A |  | 1 |
| Collector Peak Current | ICM |  |  | 7 | A | t ≤ 10 ms | 1 |
| Base Current | IB |  |  | 1 | A |  | 1 |
| Total Dissipation | Ptot |  |  | 36 | W | Tc ≤ 25 °C | 1 |
| Storage Temperature | Tstg | -65 |  | 150 | °C |  | 1 |
| Max. Operating Junction Temperature | Tj |  |  | 150 | °C |  | 1 |
| Thermal Resistance Junction-case Max | Rthj-case |  |  | 3.5 | °C/W |  | 2 |
| Thermal Resistance Junction-ambient Max | Rthj-amb |  |  | 100 | °C/W |  | 2 |
| Collector Cut-off Current (IE = 0) | ICBO |  |  | 100 | µA | for BD437/438 VCB = 45 V | 2 |
| Collector Cut-off Current (VBE = 0) | ICES |  |  | 100 | µA | for BD437/438 VCE = 45 V | 2 |
| Emitter Cut-off Current (IC = 0) | IEBO |  |  | 1 | mA | VEB = 5 V | 2 |
| Collector-Emitter Sustaining Voltage (IB = 0) | VCEO(sus) | 45 |  |  | V | IC = 100 mA for BD437/438; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |
| Collector-Emitter Saturation Voltage | VCE(sat) |  |  | 0.6 | V | IC = 2 A, IB = 0.2 A for BD437/438; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |
| Base-Emitter Voltage | VBE |  |  | 0.58 | V | IC = 10 mA, VCE = 5 V; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |
| Base-Emitter Voltage | VBE |  |  | 1.2 | V | IC = 2 A, VCE = 1 V for BD437/438; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |
| DC Current Gain | hFE | 30 |  |  |  | IC = 10 mA, VCE = 5 V for BD437/438; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |
| Matched Pair DC Current Gain Ratio | hFE1/hFE2 |  |  | 1.4 |  | IC = 500 mA, VCE = 1 V; pulsed: pulse duration 300 µs, duty cycle 1.5 % | 2 |

## CAD (KiCad official)

- Symbol: `BD438`
- Footprint: `Package_TO_SOT_THT:TO-126-3_Vertical`
- 3D model: TO-126-3 (KiCad packages3D, STEP)
- 3D model files: `bd438-etched.step` / `bd438-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `bd438.step` / `bd438.glb` are the bare package body.

## Provenance

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

- **Datasheet:** [STMicroelectronics datasheet](https://www.st.com/resource/en/datasheet/bd438.pdf) (4 pp, sha256 `eff0c287adc6d211`, retrieved 2026-09-24, tier: manufacturer)
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.2`, primary `claude-haiku-4-5-20251001` (text), consensus `claude-sonnet-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/bd438-datasheet.pdf)