Summary of How to Build a Class-D Power Amp
This article introduces the construction of a DIY Class-D audio power amplifier, highlighting its superior efficiency (80–95%) compared to linear amplifiers like Class AB. It explains that Class-D amplifiers use MOSFETs as switches rather than linear devices, resulting in minimal heat generation and the need for smaller heat sinks. The project utilizes Pulse Width Modulation (PWM) via a comparator to encode input signals into rectangular pulses, which are then amplified and passed through a low-pass filter to reconstruct the analog output.
Parts used in the Class-D Amplifier:
- MOSFETs (Power Transistors)
- Comparator
- Low-pass Filter
Have you always wanted to build your own audio power amplifier? An electronic project where you not only see the results but also hear them?
If your answer is yes, then you should continue reading this article on how to build your own Class D amplifier. I will explain to you how they work and then guide you step by step to make the magic happen all by yourself.
Theoretical Basics
What is a Class-D audio power amplifier? The answer could be just a sentence long: It is a switching amplifier. But in order to fully understand how one works, I need to teach you all its nooks and crannies.
Let’s start with that first sentence. Traditional amplifiers, like the class AB, operate as linear devices. Compare this to switching amplifiers, so called because the power transistors (the MOSFETs) are acting like switches, changing their state from OFF to ON. This allows a very high efficiency, up to 80 – 95%. Because of this, the amplifier does not generate a lot of heat and does not require a big heat sink like linear class AB amplifiers do. For comparison, the class B amplifier can only achieve a maximum efficiency of 78.5% (in theory).
Below you can see the block diagram of a basic PWM Class-D amplifier, just like the one that we are building.
The input signal is converted into a pulse width modulated, rectangular signal using a comparator. This basically means that the input is encoded into the duty cycle of the rectangular pulses. The rectangular signal is amplified, and then a low-pass filter results in a higher-power version of the original analog signal.
There are other methods for converting the signal into pulses, such as ΔΣ (delta-sigma) modulation, but for this project we will be using PWM.
Read more: How to Build a Class-D Power Amp
- What is a Class-D audio power amplifier?
It is a switching amplifier where power transistors act like switches changing state from OFF to ON. - How efficient is a Class-D amplifier compared to Class AB?
Class-D amplifiers achieve 80–95% efficiency, while traditional Class AB amplifiers operate as linear devices with lower efficiency. - Why does a Class-D amplifier generate less heat?
Because it uses switching action instead of linear operation, it does not require big heat sinks like linear Class AB amplifiers. - What method is used to convert the input signal into pulses for this project?
The project uses PWM (Pulse Width Modulation) converted by a comparator. - How is the final analog signal produced after amplification?
A low-pass filter processes the amplified rectangular signal to result in a higher-power version of the original analog signal. - Does this project use Delta-Sigma modulation?
No, while Delta-Sigma is another method, this specific project uses PWM. - What is the theoretical maximum efficiency of a Class B amplifier?
A Class B amplifier can only achieve a maximum efficiency of 78.5% in theory.
