Audio amplifier circuit and controlling method thereof

An audio amplifier circuit comprising:

• a pulse width modulation circuit coupled between a first node and a second node;
• an auxiliary loop circuit coupled between the second node and the first node, wherein the auxiliary loop circuit is corresponded to a first variable resistance value and a first variable current value;
• and
• a main loop circuit coupled between the second node, an output terminal, and the first node, wherein the main loop circuit is corresponded to a second variable resistance value and a second variable current value,
• wherein under a condition that the auxiliary loop circuit and the main loop circuit are both turned on, the second variable resistance value is decreased and the second variable current value is increased after the auxiliary loop circuit enters into a first control state such that the main loop circuit enters into a second control state, and the first variable resistance value is increased and the first variable current value is decreased after the main loop circuit enters into the second control state such that the auxiliary loop circuit is out of the first control state.