Increasing the output current of LM7805
Increasing the output current of a voltage regulator can be done with an outboard transistor.

     +--------     ------------+
     |        \&gt;__/            |
     |          |              |
IN --+---/\/\/--+----[ REG ]---+-- OUT
          Rsense        |
                        |
                       ---


When current flowing across the small-valued current-sensing resistor develops a voltage greater than 0.7V, the outboard PNP transistor turns on and begins to shunt extra current around the regulator.

The resistor is chosen such that the transistor starts to turn on before the regulator's current limit is reached. For instance, for 1A, it would be around 0.7 ohms.

There is no upper limit on this current. Whereas the regulator protects itself, the outboard transistor has no current limiting. That can be added with more components. Another transistor circuit with an even smaller current sensing resistor can kick in at some upper current value, and redirect current back into the regulator, thereby triggering its shutdown mechanism.



For instance if Q1 cannot handle much over 10A (with the heatsink we put on it and all) Rtiny can be chosen with a 0.07 ohm value. When 10A passes through it, Q2 is turned on, and starts to pass collector current into the regulator which takes care of the rest.

For the negative voltage regulator, the circuit is similar, but with NPN transistors rather than PNP.