Foldback voltage regulator

The usual senes 7805 and 7812 three-pin voltage regulators are excellent for normal applications. If currents up to 3 Aare required, an additional transistor, such as T2 in the diagram, is used. That solution works well, but the overall dissipation in case of a short-circuit can get fairly high. That creates a difficulty, particularly when a Type 7812, 7815 or 7824 is used. This difficulty may be overcome by so-called foldback regulation. This ensures electronically that the maximum current is reduced when the output voltage decreases. In the prototype, the maximurrt current with the output short-circuited was only 0.5 V so that overheating did not occur.