Patent ID: 8436683

Claim:
An audio amplifier circuit, comprising: an operational amplifier, the operational amplifier operatively connected to an audio input and an audio output; a step-up converter, the step-up converter having an output that is operatively connected to the operational amplifier and provides a variable supply voltage Vcc to the operational amplifier, the variable supply voltage Vcc being selected from a set of predetermined voltages; a first comparator configured to compare the voltage at the output of the operational amplifier with a first reference voltage Vref 1 , wherein the first reference voltage Vref 1 is selected such, that the output of the first comparator creates a first signal which indicates a need to raise the supply voltage Vcc to the operational amplifier to avoid clipping of the output of the operational amplifier; a second comparator configured to compare the voltage at the output of the operational amplifier with a second reference voltage Vref 2 , wherein the second reference voltage Vref 2 is selected such, that the output of the second comparator creates a second signal which indicates a possibility to lower the voltage of the step-up converter output without causing clipping of the output of the operational amplifier; a microcontroller, operatively connected to the step-up converter, the first comparator, and the second comparator, wherein the microcontroller is configured to raise the variable supply voltage Vcc to the operational amplifier in response to the first signal from the first comparator by Vstep, and to lower the variable supply voltage Vcc to the operational amplifier in response to the second signal from the second comparator by Vstep.