PNP Output short circuit protection

An amplifier having a current-limited output comprising:

• first and second terminals for applying supply potential therebetween;
• a third terminal at which output signal is available;
• first and second transistors of a first conductivity type and a third transistor of a second conductivity type complementary to the first, each having respective first and second electrodes and respective principal conduction paths therebetween, and having control electrodes, the principal conduction path of each transistor being controlled responsive to potential applied between its respective first and control electrodes;
• resistive means having a first end connected at the first electrode of said third transistor and a second end connected at the first terminal;
• current source means connected between the second terminal and a node connected to the control electrode of said first transistor, to which node the second electrode of said third transistor connects;
• respective means connecting the first and second electrodes of the first transistor to the third and first terminals respectively;
• means responsive to the current through the principal conduction path of said first transistor exceeding a prescribed value for diverting current from the control electrode of said first transistor;
• means connecting the second electrode of the second transistor to the control electrode of the third transistor;
• means for applying an input signal current to the first electrode of the second transistor;
• and
• means applying a potential of predetermined value between the first terminal and the control electrode of said second transistor, for determining the maximum value of current that can flow in said resistive means responsive to increase in said input signal current, irrespective of further increase in said input signal current past that required to support said maximum value of curent flow in said resistive means, and thereby limiting the maximum current to the control electrode of the first transistor.

An amplifier having a current-limited output comprising:

• first and second terminals for applying supply potential therebetween;
• first and second transistors of a first conductivity type and a third transistor of a complementary conductivity type each having respective first and second electrodes and a respective principal conduction path therebetween and having a respective control electrode, the conduction path controlled responsive to potential between the respective control and first electrodes;
• means connecting each of the second electrodes of the first and third transistors to the control electrode of the second transistor;
• means connecting the first electrode of the first transistor to the first terminal;
• a resistive means having first and second ends connected respectively to the first electrode of the second transistor and to the first terminal;
• a first current source connected between the second terminal and the second electrode of the second transistor at which point output signal current is available;
• a second current source connected between the second terminal and the first electrode of the third transistor for providing supply current to the third transistor;
• means for applying input signal to the control electrode of the first transistor;
• and
• means for applying a potential between the first terminal and the control electrode of the third transistor, which potential being determinative of the maximum potential appearing across the resistive element, and thereby determinative of the maximum current passed in the principal conduction path of the second transistor.

An amplifier having a current limited output comprising:

• a common-emitter output transistor amplifier including a first transistor having emitter, base and collector electrodes and an emitter degeneration resistor connecting its emitter electrode to a point of reference potential;
• a second transistor of conductivity type opposite to the first transistor, having emitter, base and collector electrodes, and having its collector electrode connected at the base electrode to the first transistor;
• respective means for supplying signal current to the base of the first transistor and supply current to the emitter electrode of the second transistor;
• potential generating means connected between the base electrode of the second transistor and said point of reference potential for establishing substantially constant potential therebetween, so that the potential at the emitter electrode of said second transistor, when said second transistor is caused to saturate by the means for supplying signal current, establishes the maximum potential across and therefore the maximum current through said emitter degeneration resistor.