You can generate a tiny dc supply voltage of a just a few hundred millivolts using an additional positive voltage connected to the feedback resistor of a dc-dc converter. The need for such a low-voltage rail is increasingly commonplace as supply voltages for electronic components have been decreasing steadily over the last few years. This is largely due to the decreasing size of the geometrical structures in digital circuits such as microcontrollers, CPUs, DSPs, and others. Applications in the measurement field also require low supply voltages.
For many years, linear and switching regulators had a feedback voltage of approximately 1.2 V. This voltage was generated with a bandgap circuit in a dc-dc converter IC, which determined the lowest voltage that could be set with an external resistive divider. Now, most modern voltage-regulator ICs can generate output voltages of 0.8 V, 0.6 V, or even 0.5 V.