Power amplifier circuit for audio signal and audio device using the same

A power amplifier circuit for audio signal, comprising:

• a first push-pull output stage amplifier for amplifying an audio signal;
• a second push-pull output stage amplifier for inverting and amplifying the audio signal;
• a first switching circuit for switching power for a power source line at a frequency exceeding audible frequency and feeding one of said first and second output stage amplifiers with the power;
• a second switching circuit for switching a ground current flowing from said first or second output stage amplifier to a ground at a frequency exceeding audible frequency and flowing the current to the ground;
• a first control circuit for controlling a switching period of said first switching circuit such that the power fed changes correspondingly to a level of the audio signal by comparing a level of a first ramp wave with a comparison level generated correspondingly to one of a first difference in voltage between one of the audio signal and an amplified audio signal produced by amplifying the audio signal by said first output stage amplifier and the power fed and a second difference in voltage between one of the audio signal and an amplified audio signal produced by amplifying the audio signal by said second output stage amplifier and the power fed;
• a second control circuit for controlling a switching period of said second switching circuit such that the power circulated to the ground side changes correspondingly to a level of the audio signal by comparing a level of a second ramp wave with a comparison level generated correspondingly to one of a third difference in voltage between one of the audio signal and an amplified audio signal produced by amplifying the audio signal by said first output stage amplifier and the ground current voltage from said first output stage amplifier and a fourth difference in voltage between one of the audio signal and an amplified audio signal produced by amplifying the audio signal by said second output stage amplifier and the ground current voltage from said second output stage amplifier;
• and
• a capacitor provided between the outputs of said first and second output stage amplifiers, a loud speaker being driven by outputs of said first and second amplifiers.

An audio device for amplifying an audio signal and outputting the amplified signal to a load comprising:

• a pre-amplifier circuit for amplifying the audio signal;
• a first push-pull output stage amplifier for power-amplifying the audio signal amplified by said pre-amplifier and outputting to said load;
• a second push-pull output stage amplifier for power-amplifying the audio signal amplified by said pre-amplifier and outputting to said load;
• a switching circuit for switching power from a power line at a frequency exceeding audible frequency and supplying it to said first and second amplifiers;
• a control circuit for controlling a switching period of said switching circuit such that the supplied power is changed correspondingly to a level of the audio signal correspondingly to one of a first difference in voltage between the supplied power and one of the audio signal voltage and an amplified audio signal produced by amplifying the audio signal by said first amplifier and a second difference in voltage between the supplied power and one of the audio signal voltage and the amplified audio signal produced by amplifying the audio signal by said second amplifier;
• a loudspeaker provided between the outputs of said first and second amplifiers as said load;
• and
• a capacitor provided between the outputs of said first and second output stage amplifiers.

An audio device for amplifying an audio signal and supplying an amplified signal to a load comprising:

• a pre-amplifier for amplifying the audio signal;
• a first push-pull output stage amplifier for amplifying the audio signal amplified by said pre-amplifier and supplying it to said load;
• a second push-pull output stage amplifier for amplifying the audio signal amplified by said pre-amplifier and supplying it to said load;
• a first switching circuit for switching power from a power line at a frequency exceeding audible frequency and feeding it to one of said first and second output stage amplifiers;
• a second switching circuit for switching a ground current flowing from one of said first and second output stage amplifiers to a ground at a frequency exceeding audible frequency and feeding it to the ground;
• a first control circuit for controlling a switching period of said first switching circuit such that the feeding power is changed correspondingly to a level of the audio signal correspondingly to one of a first difference in voltage between the feeding power voltage and one of the audio signal voltage and the audio signal amplified by said first output stage amplifier and a second difference in voltage between the feeding power voltage and one of the audio signal voltage and the audio signal amplified by said second amplifier;
• a second control circuit for controlling a switching period of said second switching circuit such that the power flowing to the ground is charged corresponding to a level of the audio signal correspondingly to one of a third difference in voltage between the ground current voltage from said first output stage amplifier and one of the audio signal voltage and the audio signal amplified by said first output stage amplifier and a fourth difference in voltage between the ground current voltage and one of the audio signal voltage and the audio signal amplified by said second amplifier;
• a loud speaker provided between the outputs of said first and second amplifiers as said load;
• and
• a capacitor provided between the outputs of said first and second amplifiers.