The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 29, 1993
Filed:
May. 13, 1991
Robert E Morris, Jr, Indianapolis, IN (US);
Mark R Anderson, Indianapolis, IN (US);
Thomson Consumer Electronics, Inc., Indianapolis, IN (US);
Abstract
A protection circuit for an audio output channel of a television receiver includes a detector which detects the presence of either or both of (1) a sustained DC component applied to the loudspeaker form the audio power amplifier, (2) and the loss of a supply voltage for the power amplifier. The presence of a of a sustained DC component can damage the loudspeaker. The loss of a supply voltage of the power amplifier can damage the power amplifier and can also result in the application of a sustained DC amplifier and can also result in the application of a sustained DC component to the loudspeaker. For example, the loss of the negative supply voltage of a power amplifier incorporated in an integrated circuit results in the removal of potential from the substrate which otherwise serves to electrically isolates various semiconductor devices supported by the substrate. The detector includes a low pass filter coupled between the output of the power amplifier and inputs of first and second comparators to detect when the output of the low pass filter is within or outside of a 'window'. A transistor switch is coupled to output of the comparators. As long as the output of the low pass filter is within the window, each comparator generates a respective low level output signal which keeps the transistor switch turned off. However, if the output signal of the lowpass filter is outside of the window, one of the comparators generates a high level output signal signal which causes the transistor switch to be turned on. The comparators normally receive the same supply voltages as the power amplifier, and the loss of the negative supply voltages does not enable either of the comparators to generates a low enough level output signal for keeping the transistor off.