To operate with high input voltages using a 3-terminal voltage regulator such as the LM340-15, we can use the circuit shown in the figure. This circuit is also suitable for integrated circuits that do not allow more than a 25 V input. Both the voltage regulator integrated circuit and the 2N3055 power transistor must be mounted on good heat radiators. The zener diode is 1 W. Note that in this circuit the output voltage is 15 V, but other integrated ones with different outputs may be used according to the desired application. The maximum output current of this circuit is 1.5 amps.
