This circuit converts the voltage from small fixed sources of 6 V or 12 V into 3 V for powering circuits using two small batteries. The plug for the power supply can be replaced with a 12V adapter for the car. For 6 V inputs the resistor can be 47 ohm x 2 W. The maximum current of this reducer is of the order of 50 mA. The diodes can also be 1N4004 and the capacitor can have values between 100 uF and 1000 uF.
