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

A device for amplifying an audio signal and supplying an amplified signal to a speaker, comprising:

• a preamplifier for amplifying an audio signal;
• a first output stage push-pull amplifier for amplifying the audio signal amplified by said preamplifier and supplying it to said speaker;
• a second output stage push-pull amplifier for amplifying the audio signal amplified by said preamplifier and supplying it to said speaker;
• a first switching circuit including a ramp wave generator circuit oscillating at a frequency in a range from 50 kHz to 800 kHz, a comparator having one input supplied with an output of said ramp wave generator circuit and another input supplied with a control signal and a switching transistor for ON/OFF switching of power supplied from a power source line in accordance with an output of said comparator and for feeding power to said first and second amplifiers;
• a smoothing circuit having a coil provided between the feed power output of said first switching circuit and respective terminals of said first and second amplifiers for receiving a feed power;
• a second switching circuit for forming a circulating path, in accordance with the half cycle of said audio signal to supply said first and second amplifiers with a current of said coil in a period when said switching transistor is in an OFF state;
• and
• a control circuit including a control voltage value generator circuit for generating a voltage value corresponding to a voltage difference between a voltage signal of the feed power and a voltage of one of a first output signal of said first amplifier and a second output signal of said second amplifier as the control signal and supplying the voltage value to said another input of said comparator to control the comparator output for controlling a switching period of said switching transistor such that the voltage difference between the voltage of one of said first output signal and said second output signal and the voltage of the feed power becomes substantially constant.

A power amplifier circuit for an audio signal, comprising:

• a first push-pull amplifier for amplifying an audio signal;
• a second push-pull amplifier for amplifying the audio signal;
• a first switching circuit including a ramp wave generator circuit oscillating at a frequency in a range from 50 kHz to 800 kHz, a comparator having one input supplied with an output of said ramp wave generator circuit and another input supplied with a control signal and a switching transistor for ON/OFF switching of current from one of said first amplifier and said second amplifier to a ground in accordance with an output of said comparator for grounding the current;
• a smoothing circuit having a coil provided between an input of said first switching circuit for receiving the current and a terminal of one of said first amplifier and said second amplifier for passing the current to said ground;
• a second switching circuit for forming a circulating path in accordance with the half cycle of said audio signal to supply one of said first amplifier and said second amplifier with a current of said coil in a period when said switching transistor is in an OFF state;
• and
• a control circuit including a control voltage value generator circuit for generating a voltage value corresponding to a voltage difference between a voltage signal of the current from one of said first amplifier and said second amplifier and a voltage of a pull output signal of one of said first amplifier and said second amplifier as the control signal and supplying the voltage to said another input of said comparator to control the comparator output for controlling a switching period of said switching transistor such that the voltage difference between the voltage of said pull output signal and the voltage of the current from said one of said first amplifier and said second amplifier becomes substantially constant.

A device for amplifying an audio signal and supplying an amplified signal to a speaker, comprising:

• a preamplifier for amplifying an audio signal;
• a first push-pull amplifier for amplifying an audio signal;
• a second push-pull amplifier for amplifying the audio signal;
• a first switching circuit including a ramp wave generator circuit oscillating at a frequency in a range from 50 kHz to 800 kHz, a comparator having one input supplied with an output of said ramp wave generator circuit and another input supplied with a control signal and a switching transistor for ON/OFF switching of current from one of said first amplifier and said second amplifier to a ground in accordance with an output of said comparator for grounding the current;
• a smoothing circuit having a coil provided between an input of said first switching circuit for receiving the current and a terminal of one of said first amplifier and said second amplifier for passing the current to said ground;
• a second switching circuit for forming a circulating path in accordance with the half cycle of said audio signal to supply one of said first amplifier and said second amplifier with a current of said coil in a period when said switching transistor is in an OFF state;
• and
• a control circuit including a control voltage value generator circuit for generating a voltage value corresponding to a voltage difference between a voltage signal of the current from one of said first amplifier and said second amplifier and a voltage of a pull output signal of one of said first amplifier and said second amplifier as the control signal and supplying the voltage to said another input of said comparator to control the comparator output for controlling a switching period of said switching transistor such that the voltage difference between the voltage of said pull output signal and the voltage of the current from said one of said first amplifier and said second amplifier becomes substantially constant.