Sughrue, Rothwell, Mion, Zinn and Macpeak
Temperature insensitive DC voltage detection and protection circuit
 A circuit for detecting a DC signal in the output of an audio amplifier 1 and for uncoupling a speaker SP in response thereto comprises a low-pass filter 2 whose output is coupled to one input of differential amplifiers 5, 6 whose other inputs are unbalanced by respective positive and negative threshold biasing potentials E.sub.1, E.sub.2. The differential amplifiers are directly connected to respective current mirror circuits 7, 8, and their high impedance side collector outputs are applied to the inputs of an OR circuit whose output in turn controls the speaker uncoupling. 
Pioneer Electronic Corporation
H H G
H03F H02H G01R
inventional inventional inventional
Hideo Susumu
Ito Sueyoshi