Patent ID: 7999610
Filing Date: 2011-08-16
Classification: H03F

Abstract:
1. A Class D amplifier capable of setting restraint power, the Class D amplifier comprising: an audio amplification unit, being configured to receive and amplify first input audio signals and second input audio signals to output first amplified audio signals and second amplified audio signals; a pulse width modulation (PWM) unit, being coupled to the audio amplification unit and configured to receive and perform pulse width modulation on the first amplified audio signals and the second amplified audio signals to output first pulse width modulated signals and second pulse width modulated signals; a first pre-drive unit, being coupled to the PWM unit and configured to receive the first pulse width modulated signals and control circuit units of the next stage coupled thereto according to the first pulse width modulated signals; a second pre-drive unit, being coupled to the PWM unit and configured to receive the second pulse width modulated signals and control circuit units of the next stage coupled thereto according to the second pulse width modulated signals; a first power transistor set, being coupled to the first pre-drive unit, wherein upon receiving the first pulse width modulated signals, the first pre-drive unit controls the on/off status of the first power transistor set according to the first pulse width modulated signals so that the first power transistor set outputs first output audio signals for driving an external speaker unit; a second power transistor set, being coupled to the second pre-drive unit, wherein upon receiving the second pulse width modulated signals, the second pre-drive unit controls the on/off status of the second power transistor set according to the second pulse width modulated signals so that the second power transistor set outputs second output audio signals for driving the external speaker unit; and a power restraint unit, being coupled to the audio amplification unit and an external first reference voltage and having a comparator circuit and a power restraint circuit, wherein the comparator circuit is configured to compare the high level of the first/second amplified audio signals against the level of the first reference voltage, and when the high level of the first/second amplified audio signals is higher than the level of the first reference voltage, meaning that power of the first/second output audio signals for driving the speaker unit is too high, the comparator circuit outputs a first comparison signal and a second comparison signal to the power restraint circuit, and then the power restraint circuit restrains the power of the first/second output audio signals by decreasing a DC level of the first/second input audio signals to prevent the output audio power of the first/second output audio signals from going too high and causing damage to the speaker unit.