The BD135 NPN Medium Power Transistor is a rugged and versatile semiconductor designed for applications that require more current than a standard small-signal transistor can handle. At Electrapac, we recommend the BD135 for hobbyists and professionals in Bangladesh who are building motor drivers, audio amplifiers, or power management circuits.

Product Overview

The BD135 is an NPN Bipolar Junction Transistor (BJT) housed in a SOT-32 (TO-126) plastic package. It is specifically engineered for medium power applications, capable of handling a continuous collector current of up to 1.5A. Its flat-faced design allows it to be easily mounted to a heatsink, ensuring stable performance even under heavy loads.

Key Features for Electrapac Customers

• Medium Power Capability: With a 1.5A rating, the BD135 can directly drive DC motors, large relay coils, and high-power LED arrays that would burn out a smaller BC547.

• Heatsink Compatible: The TO-126 package features a central mounting hole, allowing you to bolt the transistor to an aluminum heatsink for superior thermal management during continuous high-load operation.

• High Gain-Bandwidth Product: A 190MHz transition frequency makes it surprisingly capable in high-frequency switching and RF driver stages.

• Rugged Construction: Designed to withstand the voltage spikes common in inductive loads like solenoids and motors.

• Complementary Pairing: The BD135 is the NPN counterpart to the BD136 PNP transistor, making them a perfect pair for Class AB audio amplifier designs.

Pinout & Connection Guide

When looking at the labeled front side of the BD135 with the pins pointing downwards, the pinout is:

1. Pin 1 (Left): Emitter (Connects to Ground in typical switching).

2. Pin 2 (Middle): Collector (Connects to the Load).

3. Pin 3 (Right): Base (The control trigger).

Pro-Tip: Because the BD135 is a power transistor, its base requires more current to fully "turn on" (saturate) compared to small transistors. If you are triggering this from an Arduino or ESP32 to drive a 1 A load, use a lower value base resistor (like 220Ω or 470Ω) to ensure the transistor stays cool and efficient.

Primary Applications

• DC Motor Control: Acting as a high-speed switch for small to medium motors.

• Audio Power Amplifiers: Used in the output stages of home-built amplifiers or radio equipment.

• Relay & Solenoid Drivers: Safely triggering heavy-duty 12V or 24V relays.

• LED Strip Dimming: Handling the high current required for long lengths of LED tape.

• Voltage Regulators: Used as a pass transistor in custom-built linear power supplies.

Why Shop at Electrapac?

We source our BD135 Power Transistors with high-quality silicon wafers to ensure they meet the thermal and electrical demands of professional electronics repair and DIY innovation. Visit us at for the power components that drive your biggest ideas.