See the line going right through the middle? This line represents what we call the zero crossing point and it is where no power is being delivered to the speaker nor converted to heat. Now follow the sine wave up to the highest point it goes (as well as the lowest): called the peak (like mountain peak). This is the point where the maximum amount of power is sent to the loudspeaker - but not the point of the most heat. This is important to understand so hang in there with me.
The zero crossing point and the peak are the two points on the sine wave where the least amount of heat is generated, relative to our efficiency figure I quoted you earlier. In the case of the zero point it's rather obvious because essentially the amp is turned off. However, the peak is where we get the greatest efficiency - meaning we deliver 95% of the power to the speaker and only 5% goes to producing wasted heat.
Everywhere in between the zero point and the peak generates more heat than it does power to the speaker. Therefore, everything in between the peak and the zero is inefficient. What would be perfect, if we wanted to create a power amplifier, would be to have only the two most efficient states in use at any one time.
Class D amplifiers have three states:
- Off (zero)
- On (peak)
- Time (width)
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