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diotec (Diotec Semiconductor AG)

Diotec Semiconductor AG

https://www.diotec.com/
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Jul 10, 2026

BST62 - PNP Darlington Transistor with Anti-Parallel Diode and Resistors: Low Device Count Relay Drive for Domestic Controls

In building automation, a Darlington transistor serves as an amplifier between a control unit (e.g., a microcontroller) and a relay. Since microcontrollers often cannot supply enough current to directly drive a relay, the Darlington transistor amplifies the control signal. The high current gain makes it possible to activate the relay coil and thus switch higher-power devices. A flyback diode protects the transistor from voltage spikes when the relay is deactivated. The Base-Emitter resistors prevent unintended turn-on, ensure a defined OFF state, improve switching speed and stabilize behavior against leakage and noise. As a result, the Darlington transistor enables reliable and safe control of relays in automation systems.

Containing a PNP Darlington transistor plus diode and resistors in a single SOT-89 case outline, Diotec's BST62 allows design engineers to build a relay drive at lowest board space and without the need of further external components. An input current of as low as 190 µA allows to drive a 150 mA relay coil. Its collector voltage of up to 110 V allows operation on 24 V DC bus rails.

Features:

  • PNP Darlington transistor

  • Antiparallel diode

  • Base-Emitter resistors

  • High current gain

Applications:

  • Domestic controls

  • Smart home systems

  • KNX devices

  • LED drivers

  • Relay drivers

  • Control Circuits

Specifications:

  • 1 A DC Collector current (-IC)

  • 110 V Collector-Emitter voltage (-VCEO)

  • Minimum DC current gain of 800 at –IC = 150 mA (hFE)

  • Power dissipation 1.3W at 25°C (Ptot)

  • SOT-89 case outline