Patent ID: 7764797
Filing Date: 2010-07-27
Classification: H03F,H03G

Abstract:
1. A speaker driving device for driving speakers of a plurality of types with different load impedances, comprising: an output terminal to which a speaker among a plurality of types selected is connected; a power supply terminal to which a voltage corresponding to a load impedance of a speaker connected to the output terminal is applied; a power supply voltage detection circuit for determining a type of speaker connected to the output terminal based on a voltage applied to the power supply terminal; an amplifier circuit for amplifying an input signal to drive a speaker connected to the output terminal with a voltage applied to the power supply terminal as a source of power; and a gain switching circuit for switching a gain of the amplifier circuit to a gain corresponding to a type of speaker connected to the output terminal as determined by the power supply voltage detection circuit so that when the same input signal is applied to any one of the plurality of types of speakers, the same output power of the amplifier circuit is produced, wherein the amplifier circuit amplifies the input signal by a gain switched by the gain switching circuit.