ICs requiring 3 or 6 volts can be run from a battery or fixed regulated supply of a higher voltage by using the circuit shown. The transistor should be mounted on a heatsink as considerable power will be dissipated by its collector. Additional filtering can be obtained by fitting a capacitor (Cl) as shown. The capacitance is effectively multiplied by the gain of the transistor, A ripple of 200 mV (peak to peak) at the input can be reduced to 2 mV in this fashion
Maximum output current depends on the supply rating and transistor type (with heatsink) - used.