In this circuit the output current is limited by R3. For a 300 mA current, R3 must have 12 Ω. For 500 A the value is 1.2 A and for 1 A the value is 0.68 ohm. The transistor must be mounted on a heatsink. Equivalent transistor can be used. Input voltage can range from 9 to 14 V.
