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Power Amplifier With Output Stage Protect Circuit

IP.com Disclosure Number: IPCOM000075120D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Lamoreaux, WG: AUTHOR

Abstract

In the above power amplifier circuit, a class B(2) output stage comprises a complementary series push-pull configuration driven from a full Darlington (I-Mode) push-pull inverting stage. Transistors 10 and 11 which form the class B(2) stage consist of a power emitter-follower and collector-loaded amplifier, respectively, each transistor operating into clamping diodes 12 and 13 across the matching auto transformer 14. A load device, such as a transducer coil 15 of an air horn 16, or the like, is connected across the auto transformer 14. Transistors 17 and 18 with associated circuit resistors and capacitors form the full Darlington push-pull inverting stage.

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Power Amplifier With Output Stage Protect Circuit

In the above power amplifier circuit, a class B(2) output stage comprises a complementary series push-pull configuration driven from a full Darlington (I- Mode) push-pull inverting stage. Transistors 10 and 11 which form the class B(2) stage consist of a power emitter-follower and collector-loaded amplifier, respectively, each transistor operating into clamping diodes 12 and 13 across the matching auto transformer 14. A load device, such as a transducer coil 15 of an air horn 16, or the like, is connected across the auto transformer 14. Transistors 17 and 18 with associated circuit resistors and capacitors form the full Darlington push-pull inverting stage.

The protect circuit for the class B(2) output stage comprises NPN transistor 19 and PNP transistor 20, which are connected across resistors R1 and R2 to form a "crow-bar" circuit. This crow-bar circuit is essentially a nonlinear amplifier, which serves as a fast-acting high current "sink" to protect the output circuit from accidental shorts or overloads. Specifically, if shorting or overloading occurs in transducer coil 15, an increased current flows in resistors R1 and R2 in the emitter and collector circuits of transistors 10 and 11, respectively. The voltage drops across R1 and R2 causes base voltage cutoff in transistors 19 and 20, removing all signal-drive from the Darlington driver and class B power-output stage.

In a specific application, the various com...