Why are class D amps so much more efficient?

Don’t understand why class D amps are so much more efficient than A/B? The power supply is off part of the time, and on full power the rest of the time. Music is rarely off, so class D must be limited in how long the power supply can be off. Where are class D amps gaining all the efficiency?


The relatively simple answer is that class D amplifiers control their output power devices by turning them fully on and fully off (rapidly). The more traditional class A/B for example has the output power devices partially on at all times (based on level of bias current) and top and bottom devices are turned on more or less based on the music signal. Power devices have higher losses (lower efficiency) when they are partially on versus fully on and off.


@kcleveland123 now it makes sense. Amazing the “inbetween” is so inefficient. People are quick to point out class D doesn’t stand for digital. But, switching the power supply on & off sure seems more digital than analog?

The power supply is not being switched on and off. The output devices are.

I suggest some googling of various electronics concepts. Asking for quick easy answers to complex engineering problems will not lead to better understanding but it may lead to worse understanding.

Don’t some class D amps have switching power supplies also?

Yes they have switching power supplies but that’s not where the main efficiency comes from. You can use a switching supply on a class A amp and it will still operate like an oven.

Switching PSUs are more efficient than linear PSUs but not by a massive amount. As I said above, it’s the output devices and how they operate that makes the big deal in efficiency.

I should clarify my previous statement - yes switching supplies do have devices that switch on and off. But in an audio amplifier that’s not where you get the biggest efficiencies.

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