I recently reversed engineered a discrete voltage regulator from a board that was performing quite well, and I stumbled upon a weird transistor pair circuit.

^{simulate this circuit – Schematic created using CircuitLab}

The zener here is just to make the circuit works, the regulator is actually based on a TL431 shunt regulator.

I looked for some time in the literature and dug into some schematics and cannot find any references to that kind of transistor pair. Does they have a name ? What would be the advantage of such an arrangement versus a simple BJT or even a Darlington?

I recently reversed engineered a discrete voltage regulator from a board that was performing quite well, and I stumbled upon a weird transistor pair circuit.

^{simulate this circuit – Schematic created using CircuitLab}

The zener D1 is a TL431 shunt regulator in the real circuit. I put a 5.8V zener just to make the simulation works.

I looked for some time in the literature and dug into some schematics and cannot find any references to that kind of transistor pair. Does they have a name ? What would be the advantage of such an arrangement versus a simple BJT or even a Darlington?