Over-current prevention circuitry for transistor amplifiers

Amplifier circuitry comprising:

• first and second terminals for receiving a fixed operating potential therebetween;
• a transistor having base and emitter and collector electrodes, having a base-emitter junction between its base and emitter electrodes and having a variable-conduction path between its collector and emitter electrodes the conduction of which is regulated responsive to current through its base electrode;
• load means serially connected with the variable conduction path of said transistor between said first and said second terminals;
• controlled current source means for supplying a current proportionally responsive to the potential across said load means, said current increasing and decreasing as the potential across said load means respectively increases and decreases, the proportionality between said proportionally responsive current and the potential across said load means so chosen as to avoid operation of said transistor outside its Safe Operating Area Rating;
• and
• means for applying, so long as available from said controlled current source means, a portion of said current linearly related to the potential across said load means, which portion is applied to the base electrode of said transistor and is linearly responsive to swings of an input signal in one polarity.

Push-pull amplifier circuitry comprising:

• first and second terminals for receiving an operating potential therebetween;
• a third terminal for receiving an input signal;
• a fourth terminal for output signal responsive to said input signal;
• first and second and third and fourth transistors of a first conductivity type and fifth and sixth transistors of a second conductivity type, each transistor having base and emitter and collector electrodes;
• first and second direct current conductive means connecting the collector electrodes of said second and said third transistors to said first terminal;
• a first circuit node to which said third terminal is direct coupled;
• means for direct coupling said first circuit node to the base electrode of said first transistor;
• means for direct coupling said first circuit node to the base electrode of said third transistor;
• a second circuit node to which said fourth terminal is direct coupled;
• means for direct coupling said second circuit node to the base electrode of said second transistor;
• means for direct coupling said second circuit node to the base electrode of said fourth transistor;
• means for direct coupling the collector electrode of said first transistor to the base electrode of said fifth transistor;
• means for direct coupling the collector electrode of said fourth transistor to the base electrode of said sixth transistor;
• third and fourth direct current conductive means connecting the respective emitter electrodes of said fifth and said sixth transistors to said first terminal and to said fourth terminal, respectively;
• fifth and sixth direct current conductive means connecting the respective collector electrodes of said fifth and said sixth transistors to said fourth terminal and to said second terminal, respectively;
• a third circuit node to which the emitter electrodes of said first and said second transistors are connected;
• a fourth circuit node to which the emitter electrodes of said third and said fourth transistors are connected;
• first current source means connected between said second terminal and said third circuit node for establishing the combined emitter current flows of said first and said second transistors;
• and
• second current source means connected between said second terminal and said fourth circuit node for establishing the combined emitter current flows of said third and said fourth transistors.

In a transistor amplifier having output transistor means with a control electrode and with an output circuit arranged for completing a circuit including a power supply and load;

• having over-current protection circuitry of the type comprising a constant current generator for supplying a bias current sufficiently constrained in magnitude that, if applied in full to the control electrode of said output transistor means, said output transistor means would be provided protection against over-dissipation;
• and having means responsive to input signal for applying a changing portion of the current from said constant current generator to the control electrode of said output transistor means, an improvement wherein said constant current generator provides substantially temperature-independent bias current and wherein the adverse effects of applying portions of a temperature-independent bias current to the output transistor means are forestalled by said output transistor means comprising:
• first and second transistors of the same conductivity type, each having base and emitter and collector electrodes, the control electrode of said transistor means being similarly direct coupled to each of the respective base electrodes of said first and said second transistors and having the collector electrode of said second transistor galvanically connected thereto;
• and
• the collector electrode of said first transistor being galvanically connected to a first end of the output circuit of said output transistor means;
• and
• first and second resistances of relatively low and relatively high value, having respective first ends respectively connected to the emitter electrode of said first transistor and to the emitter electrode of said second transistor, and having respective second ends connected together and to a second end of the output circuit of said output transistor means remote from its first end.