A D-class audio amplifier is a device designed to reproduce a signal applied to the input of the device using input circuit elements, with a given volume and power level, with a minimum value of energy dissipation and distortion. The use of such amplifiers began in 1958, but recently their popularity has increased markedly. Why is a D-class amplifier so good? In this article, we will try to answer this question.
In a conventional amplifying device, the output stage is built on semiconductor elements-transistors. They provide the required value of the output current. Many audio systems have class A, B, and AB amplifier stages. Compared to the output stage implemented in class D, the power dissipation in the linear stages is significant even when assembled perfectly. This factor provides class D with a significant advantage inmost applications, as a result of low heat generation, small overall dimensions, low product cost, and extended device life.
Class D audio amplifiers have much lower power dissipation than class A, B and AB amplifiers. The keys in the output stage of such an amplifier connect the output, negative and positive power rails, thereby creating a series of pulses with a positive and negative potential. Due to the shape of such a signal, a D-class amplifier significantly reduces the dissipated power, because in the presence of a potential difference, the current practically does not pass through the output transistors (the transistor is in the closed state). If the transistor is in open mode and current flows through it, a negligible voltage drops across it. Instantaneous power dissipation in this case is minimal.
Despite the fact that a class D power amplifier dissipates a small amount of thermal energy compared to linear amplifiers, there is still a danger of overheating the circuit. This can happen when the device is running at full power for a long time. To prevent this process, it is necessary to include temperature control circuits in the D-class amplifier. In elementary protective circuits, the output stage is turned off when its temperature, measured by the built-in sensor, exceeds the temperature threshold and will not turn on until the temperature drops to normal. Of course, it is possible to apply more complex schemes for temperature control. For example,by measuring the temperature, the control circuits can gradually lower the volume, thereby reducing heat generation, as a result, the temperature will be kept within the required limits. The advantage of such schemes is that the device will continue to work and will not turn off.
D-class amplifiers have a drawback - when the device is turned on and off, clicks and pops occur in it, which can annoy users. This effect can occur in case of “aging” or installation of a low-quality modulator, as well as synchronization of the output stage with the state of the LC filter during turning the device on and off.
