It's a temperature independent voltage reference with transistor only.
Vref = 1.278V. In the temperature range 0-50 °C, the output voltage varies by 0.056%. (Boundary condition: Input voltage = 5V)
Oscillogram from LTSpice:
This circuit is part of an ongoing power supply project.
Varga Laszlo - https://vargalaszlo.com - [email protected]
Project Link: https://github.com/vargalaszlo87/widlar-bandgap