STMicroelectronics has developed the world's first commercial audio amplifier integrated circuits to use the class D technique. Called TDA7480, TDA7481 and TDA7482, these circuits are already in production and more than 150,000 parts have been delivered to customers.

Conventional audio amplifiers ICs operate in class AB, which means that their output stages operate linearly. Class D amplifiers use switching techniques -- like in a switch-mode power supply -- so the power stage is a simple switch. The advantage of the class D technique is that the circuit is more efficient and less power is wasted. In a class AB amplifier, in the condition of maximum dissipation often used for thermal dimensioning, the efficiency is only 50%, so as much power is wasted as is delivered to the speaker. In a class D equivalent the efficiency is around 90% so only 10% of the power is wasted as heat. Apart from the saving in energy, the benefit of this higher efficiency is that less heat is generated inside the amplifier, so bulky power packages and heatsinks can be eliminated. Further savings result from the reduced demand on the power supply, which can be made smaller, lighter and cheaper.

Designers may choose a class D amplifier to achieve the same power in a simpler package. For example, TDA7480 10W class D amplifier in a 20-lead DIP package will replace a conventional linear amplifier in the Multiwatt power package with a heatsink. Alternatively, the greater efficiency of the class D amplifiers can be used to obtain greater power with the same package and heatsink -- a class D amplifier in a Multiwatt package will deliver up to five times as much power as a class AB type.

In the past class D amplifiers were too costly for most applications because the only commercial solutions available used discrete power transistors, but by combining proprietary BCD2 bipolar-CMOS-DMOS mixed technology and several years experience designing discrete class D circuits STMicroelectronics has solved this problem, creating cost-effective practical integrated circuits that are already available in production quantities.

The holy grail of audio amplification! I built my first Class-D amplifier from a kit in the 60's. Didn't work, but then the company that supplied it didn't last long either. But since that time there have been multiple attempts to get commercial devices that would do the job. Seems like SGS-Thompson (it is still difficult to think of them as STMicroelectronics) is there first although I think there will be a couple of more announcements in the near future. If any of those is for a stereo or quad device that has 15+ W of output it will commercially eclipse these mono products -- in time.

Because they are there first and even though the products are only mono they will do extremely well in a short product life. This area will now burdgeon like crazy in the next year. But remember with Class-D that you don't win every benefit every time, you have to compromise your design between efficiency and higher output power.