15 amp current boost regulator - MC78TXX

This circuit uses an MC78TXX voltage regulator to form a 15 amp current boost regulator. The 2N4398 PNP transistor provides current to 15 amps. Resistor R in conjunction with the Vbe of the PNP determines when the pass transistor begins conducting. For example, if R=0.3 ohm, the transistor will start conducting at about 2.0 amps passing through the MC78TXX. This circuit is not short circuit proof. Input-output differential voltage minimum is increased by Vbe of the pass transistor.