Although there is an enormous amount of 12 V voltage regulator integrated circuits, it may be that the reader may need to improvise one, or more, to obtain an output voltage that can be adjusted in a range around 12 V with some ease and with current reaching 2 or 3 A. For this purpose, the circuit shown in figure 8 is a good solution, even with the possibility of being modified to provide other voltage ranges such as 6, 9, 15 V, etc. The zener diodes can have slightly different voltages and the output voltage is adjusted in trimpot P1. The transistor must be equipped with a good heat radiator, depending on the current that will be drained by the load circuit. We observed that the input voltage must be between 3 V above the desired voltage at the output and a maximum of 30 V. It will not be necessary to provide the symmetrical operational amplifier.
