Amplifier with over-current protection

An amplifier with over-current protection comprising:

• an input terminal for receiving an input signal current;
• an output terminal for connection to a load;
• a common terminal for connection to an operating potential;
• transistor means having a base electrode connected to said input terminal, having a collector electrode connected to said output terminal, and having an emitter electrode;
• a resistive element with substantially constant resistance connecting the emitter electrode of said transistor means to said common terminal and responsive to the emitter current of said transistor means to develop a potential proportional to that current between said common terminal and said emitter electrode;
• a source providing a potential with reference to said common terminal, which potential is responsive to said operating potential so as to decrease as said operating potential decreases below a threshold potential;
• and
• a unilaterally conductive device connecting said source to the base electrode of said transistor means, the direction of relatively easy conduction through said device being such as to limit the excursion of signal potential appearing responsive to said input signal current between the base electrode of said transistor means and said common terminal.

An amplifier with over-current protection comprising:

• an input terminal for receiving an input signal current;
• an output terminal for connection to a load;
• a common terminal for connection to an operating potential;
• transistor means having a base electrode connected to said input terminal, having a collector electrode connected to said output terminal, and having an emitter electrode;
• a resistive element connecting the emitter electrode of said transistor means to said common terminal and responsive to the emitter current of said transistor means to develop a potential proportional to that current between said common terminal and said emitter electrode;
• a source providing a potential with reference to said common terminal, which potential is responsive to said energizing potential so as to decrease as said energizing potential decreases below a threshold potential, and is responsive to the temperature of said transistor means so as to decrease as said temperature increases;
• and
• a first unilaterally conductive device connecting said source to the base electrode of said first transistor means, the direction of relatively easy conduction through said device being such as to limit the excursion of signal potential appearing responsive to said input signal current between the base electrode of said transistor means and said common terminal.

An amplifier with over-current protection comprising:

• an input terminal, an output terminal and a common terminal, said output and common terminals for providing an output current responsive to an input current received between said input and common terminals;
• a first transistor of a first conductivity type having a base electrode coupled to said input terminal and having an emitter and a collector electrode;
• a second transistor of a second conductivity type having a base electrode direct coupled from said first transistor collector electrode, having an emitter electrode direct current conductively coupled to said output terminal, and having a collector electrode to which said first emitter electrode is direct coupled;
• means for limiting the range of potential excursions appearing between said first transistor base electrode and said common terminal, which potential excursions occur responsive to said input current;
• a resistive element coupling said second transistor collector electrode to said common terminal and proportionally responsive to collector current of said second transistor to develop a potential proportional to that current between said first transistor base electrode and said common terminal;
• and
• at least one further transistor of said second conductivity type having a base electrode direct coupled from said first transistor collector electrode, an emitter electrode direct current conductively coupled to said output terminal, and a collector electrode direct current conductively coupled to said common terminal other than through said resistive element.

The combination of:

• a composite transistor comprising a plurality of transistors of one conductivity type connected base-to-base, connected emitter-to-emitter to an output terminal, and all except one connected collector-to-collector to an operating voltage terminal, and an input transistor of another conductivity type connected at its collector to all of said bases, at its base to an input signal terminal, and at its emitter to the collector of said one of said plurality of transistors;
• a current sensing element connected between said emitter of said input transistor and said operating voltage terminal;
• and
• means responsive to the sensing by said element of more than a given level of current for limiting to a given value the potential at said input signal terminal.