# BD135

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

The BD135 is an NPN medium-power transistor rated for 45 V and 1.5 A continuous collector current in a TO-126 package. It is the lower-voltage member of the BD135/137/139 NPN series, used in audio driver and output stages, discrete regulators, and medium-power switching.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | E | passive | Emitter. Common-emitter reference for the NPN device. VEBO max = 5 V; typically tied to the low-side rail or output node depending on topology. |
| 2 | C | passive | Collector. Electrically connected to the metal mounting tab. VCBO max = 45 V, VCEO max = 45 V, IC max = 1.5 A continuous (3 A peak). Thermal path to case: Rthj-case = 10 °C/W. |
| 3 | B | input | Base. Controls collector current via base-emitter forward bias. VBE(on) ≈ 1 V at IC = 0.5 A; VEBO absolute max = 5 V; IB max = 0.5 A. |

## Key specifications

| Parameter | Value |
|---|---|
| Type | NPN medium-power transistor |
| Collector-emitter voltage (VCEO) | 45 V |
| Collector current (IC) | 1.5 A continuous (3 A peak) |
| DC current gain (hFE) | 40 to 250 |
| Transition frequency (fT) | 190 MHz |
| Power dissipation | 12.5 W |
| Operating temperature | -55 C to 150 C |

## Ordering variants

- `BD135`
- `BD135-16`

## 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 | 3 |
| Collector-emitter voltage | VCEO |  |  | 45 | V | IB = 0 | 3 |
| Emitter-base voltage | VEBO |  |  | 5 | V | IC = 0 | 3 |
| Collector current | IC |  |  | 1.5 | A |  | 3 |
| Collector peak current | ICM |  |  | 3 | A |  | 3 |
| Base current | IB |  |  | 0.5 | A |  | 3 |
| Total dissipation | PTOT |  |  | 12.5 | W | Tc ≤ 25 °C | 3 |
| Total dissipation | PTOT |  |  | 1.25 | W | Tamb ≤ 25 °C | 3 |
| Storage temperature | Tstg | -65 |  | 150 | °C |  | 3 |
| Max. operating junction temperature | Tj |  |  | 150 | °C |  | 3 |
| Thermal resistance junction-case | Rthj-case |  |  | 10 | °C/W |  | 3 |
| Thermal resistance junction-ambient | Rthj-amb |  |  | 100 | °C/W |  | 3 |
| Collector cut-off current (NPN) | ICBO |  |  | 0.1 | µA | VCB = 30 V | 4 |
| Collector cut-off current (NPN) | ICBO |  |  | 10 | µA | VCB = 30 V, TC = 125 °C | 4 |
| Emitter cut-off current (NPN) | IEBO |  |  | 10 | µA | VEB = 5 V | 4 |
| Collector-emitter sustaining voltage (NPN, BD135) | VCEO(sus) | 45 |  |  | V | IC = 30 mA | 4 |
| Collector-emitter saturation voltage (NPN) | VCE(sat) |  |  | 0.5 | V | IC = 0.5 A, IB = 0.05 A | 4 |
| Base-emitter voltage (NPN) | VBE |  |  | 1 | V | IC = 0.5 A, VCE = 2 V | 4 |
| DC current gain (NPN) | hFE | 25 |  |  |  | IC = 5 mA, VCE = 2 V | 4 |
| DC current gain (NPN) | hFE | 40 |  | 250 |  | IC = 150 mA, VCE = 2 V | 4 |

## CAD (KiCad official)

- Symbol: `bd135.kicad_sym`
- Footprint: `bd135.kicad_mod`
- 3D model: TO-126 body from KiCad `Package_TO_SOT_THT/TO-126-3_Vertical`.
- 3D model files: `bd135-etched.step` / `bd135-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `bd135.step` / `bd135.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/bd135.pdf) (9 pp, sha256 `9a72cdfa334700b8`, retrieved 2026-08-17, tier: manufacturer)
- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/bd135-datasheet.pdf)