Solved is not the same as optimised.
Every engineer knows this.
Not every engineer applies it to the circuits they stopped thinking about.
The transistor. The flyback diode. The base-emitter resistors.
Passed down through reference designs.
Proven. Unquestioned.
The circuit was correct. The component count was a habit.
The BST62 is what happens when someone finally optimises one.
PNP Darlington transistor, anti-parallel diode, and base-emitter resistors – one SOT-89 package. Nothing external.
190 pA drives a 150 mA relay coil directly from a microcontroller GPIO.
Up to 110 V VCEO – headroom for every spike the relay throws at switch-off.
Current gain minimum 800. Your microcontroller barely notices the relay is there.
One footprint.
The relay drive you’d have designed – if you’d been the first to design it.
For domestic controls, smart home systems, KNX devices, and building automation.
For the engineers who aren’t done when it works.