In the figure we show a means of changing the output voltage of a fixed regulator, such as 7805 or 7806, to obtain a higher voltage with reference to a TL431. The reference voltage VREF will be added to the voltage of the regulator, this voltage being given by the relationship between R1 and R2 as follows:
Vo = (1 + R1 / R2) Vo
For the values indicated on the circuit we have an output voltage of 9 V when the voltage regulator is 7805. The output will be 10 V for 7806. The input voltage in this case is 14.0 of a car battery, but other input voltages can be used. The integrated circuit shall be provided with a suitable heat radiator and the maximum output current of the configuration is 1 A.
