A class D amplifier is not a digital amplifier but a switching amplifier. The class D amplifier converts the analog signal (input) into a PWM waveform. The PWM modulator is not an ADC converter (as many think) but a frequency modulator that creates a sort of pulse train corresponding to the amplitude and frequency of the input signal. This process appears digital but this is analog. The signal is not "digitized", assigned to a numerical value; the PWM pulse train is an "analog" version of the input audio signal. The PWM waveform drives the push-pull MOSFET output stage fully on or off for each pulse. When one of the MOSFETs is on, the current flowing through it is high, but the voltage is very low, so the power is dissipated only during the short transitions between the on and off state. Similarly, when the MOSFET is off, the voltage across it is high, but the current is nearly zero. There is no power dissipation except in the on / off state transitions. The amplified PWM waveform, before being transferred to the speakers, is subjected to low-pass filtering to recover the audio waveform and to eliminate spurious ultrasonic noise.
Converting the analog waveform to a PWM waveform is done by applying the analog waveform to one input of a comparator, while a triangular waveform is applied to the other input. The pulse width varies according to the width of the input signal.
Class D amplifiers were first made in the 1950s. Why have they only recently gained more widespread popularity? The answer involves several factors. Until the 1980s, there were no switching transistors that met the performance needs of Class D amplifiers, and it was only in the mid 1990s that Class D ICs became available. switching frequency of 250 kHz or higher. During the 1990s, the combination of dedicated integrated circuits and continuous improvements in silicon-based power MOSFETs contributed to an acceleration in the adoption of Class D in high-end audio systems.
The choice of the amplifier board is the first step for realize a custom power amplifier. To this end you will need to consider the following factors:
1) the load impedance of the speakers that you want to drive, expressed in Ohms;
2) the power that you need, espressed in watts;
3) the impedance of the input signal, expressed in Ohms;
For the less experienced, our staff is always available for any kind of advice in this regard. Requests may be made by mail at no additional cost.