To provide a voice output circuit having a speaker save circuit stably operating when activating a power supply and changing a headphone and a protection function to the short-circuiting of a speaker drive terminal.
The voice output circuit comprises a precharge circuit, a comparator 12, and a speaker drive circuit. The precharge circuit has first and second resistors 13, 14 connected between a power terminal and a ground terminal in cascade, and a capacitor 15 whose one end is connected to the connection section of the second resistor; and outputs voltage to the voltage, where a power terminal voltage is divided by the first and second resistors, to a charge voltage terminal 35 by simultaneously starting charging when voltage is applied to the power terminal. The comparator 12 outputs a result, where an input terminal is connected to the charge voltage terminal for comparing with a reference voltage. In the speaker drive circuit, the continuity of speaker drive signals is broken according to the output signal of the comparator 12. When the voltage of the charge voltage terminal 35 is lower than a reference voltage value, the speaker drive circuit is broken. Contrarily, when the voltage of the charge voltage terminal 35 is higher than the reference voltage, the speaker drive circuit conducts electricity.
FUJII KEIICHI
Tomoyasu Sakaguchi
Hiroki Naito