Amplifier D-class - what is its popularity?

The D-Class audio amplifier is a device designed to reproduce the signal applied to the input of the device, using the elements of the input circuit, with a given volume and power level, with a minimum value of energy dissipation and distortion. The use of such amplifiers began back in 1958, but recently their popularity has increased noticeably. What is so good about the D-class amplifier? In this article we will try to answer this question.

In a conventional amplifying device, the output stage is built on semiconductor transistors. They provide the required output current. Many audio systems have amplifying cascades of class A, B and AB. If compared with the output stage implemented in class D, the power dissipation in linear stages is significant even with ideal assembly. This factor provides class D with a significant advantage in most applications, as a result of low heat generation, small overall dimensions, low product costs and increased device life.

Class D sound amplifiers have a dissipated power much lower than amplifiers A, B and AB classes. The keys in the output stage of such an amplifier connect the output, negative and positive power lines, thereby creating a series of pulses with a positive and negative potential. The D-class amplifier, due to the shape of this signal, significantly reduces the dissipated power, because in the presence of a potential difference, the current through the output transistors practically does not pass (the transistor is in a closed state). If the transistor in an open mode and through it passes a current, on it the insignificant pressure falls. Instantaneous power dissipation in this case is minimal.

Despite the fact that the Class D power amplifier dissipates a small amount of thermal energy in comparison with linear amplifiers, there is still a danger of overheating the circuit. This can happen when the unit is operated for a long time in full power mode. To prevent this process, it is necessary to include temperature control circuits in the D-class amplifier. In elementary protective schemes, the output stage is turned off when its temperature measured by the integrated sensor exceeds the temperature threshold and does not turn on until the temperature has dropped to normal. Of course, it is possible to use more complex schemes for temperature control. For example, by measuring the temperature, the control circuits can gradually lower the volume, thereby reducing heat generation, and the temperature will be kept within the required limits. The advantage of such schemes is that the device will continue to operate and will not shut down.

D-Class amplifiers have a drawback - when the device is turned on and off, there are clicks and pops that can irritate users. This effect can occur in the case of "aging" or installation of a poor-quality modulator, as well as synchronization of the output stage with the state of the LC-filter during power on and off.