To execute a mute process instantly at a transition from a power-on state to a power-off state, and prevent the mute process from being executed upon an input supply voltage drop in the power-on state.
In a power-on state, a resistance R17 and a transistor Q11 are directly connected without the intervention of a Zener diode D13. Even if an input supply voltage drops in the power-on state, transistors Q12, Q13 remain on to keep a mute control signal for executing a mute process from being output. At a transition from the power-on state to a power-off state, the resistance R17 and the transistor Q11 are connected via the Zener diode D13. An input supply voltage drop can then cause the Zener diode D13 to draw a current to the resistance R17 to instantly control the transistors Q12, Q13 to an off state and instantly output the mute control signal for executing the mute process.
UMETSU NORIO
MINAGAWA ATSUSHI
