Class D amplifiers
Class D switching amplifiers work by rapidly switching the output transistors between on and off states, rather than using linear techniques to vary the output voltage. The input audio signal is first converted to a pulse width modulated (PWM) signal, which is used to control the on and off states of the output transistors. This allows for very high efficiency, as the transistors are only on for a small portion of the time, which minimizes power loss.
The PWM signal is created by comparing the input audio signal to a high-frequency triangular waveform, known as the carrier signal. The width of the resulting PWM signal is proportional to the amplitude of the input audio signal. The PWM signal is then used to switch the output transistors on and off at a high frequency, typically several hundred kilohertz.
A low-pass filter is then used to remove the high-frequency carrier signal and recover the original audio signal. The overall efficiency of a class D amplifier can be greater than 90%.
Diagrams that may be useful to understand class D switching amplifiers can be found in resources such as:
https://www.electronics-tutorials.ws/amplifier/class-d-amplifier.html
https://www.circuitstoday.com/class-d-amplifier-circuit
https://www.electronics-notes.com/articles/analogue_circuits/amplifiers-linear/class-d-amplifiers-principles-design.php
Class D amplifiers offer several advantages over class AB amplifiers, which are the most common type of linear amplifier. The main advantage of class D amplifiers is their high efficiency, which is typically greater than 90%. This is because the output transistors are only on for a small portion of the time, which minimizes power loss. In contrast, class AB amplifiers have an efficiency of around 50%.
Another advantage of class D amplifiers is their smaller size and weight. This is because they do not require large heat sinks to dissipate heat, as the output transistors are not on for long periods of time. This makes class D amplifiers a popular choice for portable and mobile applications.
Class D amplifiers also have a lower output impedance than class AB amplifiers, which can help to improve stability and reduce distortion. One disadvantage of class D amplifiers is that they can produce higher levels of distortion than class AB amplifiers, especially at low frequencies. However, this can be minimized by using high-quality components and proper circuit design.
Another disadvantage of class D amplifiers is that they can generate electrical noise that could interfere with other electronic devices. These noise can be mitigated by using a proper filter.
In summary, class D amplifiers offer higher efficiency, smaller size and lower output impedance than class AB amplifiers, but they may produce more distortion and electromagnetic interference