Better Quality of Sound with Class D Audio Amplifier PCB

(This project is being managed here: Project Repository )

What is Class D Amplifier?

As the name suggests D, is a digital amplifier. It is also known as a switching amplifier that uses the transistors and MOSFETs as electronic switches and performs quickly switching between the supply rails. There is a modulator available in this amplifier that shifts the sampling frequency to the highest frequency. That is why they are used in audio amplifiers to enhance the quality of sound. Using pulse width modulation, this amplifier converts the input (analog) signal to digital pulses. Their efficiency varies from 80% to 95%.

Comparison with other Amplifiers:

Class A:

It is an analog amplifier that always runs at full power. When there's no signal, the transistors’ power turns into heat. When there is a signal, the power goes out to the speaker terminals. Like the D class amplifier, they do not have an on-off state of the transistors instead that is why they are always constant bias. They are less efficient than the D class amplifier. They are expensive, bulky, and not suitable for car audio systems.

Class B:

Class B amplifiers have push-pull arrangements. Only one transistor remains on for the first half cycle while for the second half cycle the other transistor gets on. One transistor amplifies the negative part of the AC signal and the other is responsible for the positive part of the signal, thus, both of them are combined together to form a unified output. They perform cross-over distortion while turning the one on and the other off and vice versa. They are more efficient than A class amplifiers but are not suitable for achieving good sound quality due to the cross-over distortion.

Class AB:

This amplifier is a combination of both A and B amplifiers. They also have a push-pull pair of transistors to get the output. They don't turn on and off suddenly either. When the signal's at low power and conducting through both transistors it will be working as a class A amplifier that runs on full power always, and when the power is high it will be working as a class B amplifier. This amplifier is more efficient than A-class and has less distortion than class B. But as compared to the D class it is still less efficient.

As a result of this comparison, the Class D amplifier is more efficient and less distorted than the above-mentioned amplifiers and it is an accurate choice for achieving good quality of sound in music.

Block diagram:

This class D amplifier works on the principles of the following block diagram. In this diagram, the analog signal is given as an input signal to the comparator or modulator. This modulator converts the analog signal to the digital pulse signal. This digital rectangular pulse has low amplitude when it passes through the low pass filter it will increase the amplitude of the original signal. At this stage, we are enhancing the quality of improving the sound level of the original signal. Then it will be converted again into an analog signal and a sound can be heard in the speakers. Now this time, you will be enjoying the music of better quality.

Working:

The schematic diagram consists of a high pass filter followed by a low pass filter at the input stage. The ICs LM393P are acting as a comparator for the amplifier. In my design, I have used two comparators; one for the highest side of the driver and the other for the lowest side of the driver. They are using a bipolar supply of 5V which is provided by the Zener diodes because they regulate the voltages from the 30V. To drive the MOSFET in the circuits, I have used IC IR2110PBF. It uses 12V to drive the MOSFET which is provided by a transistor named BD241C and a Zener diode. In this part of the circuitry, we are shifting the level of the signals provided by the comparator using the transistor and a diode. Then there is a low pass filter to amplify the original signal, to filter the signal we are using the Butterworth filter. I have used LMC555CN_NOPB IC to generate the triangular wave. With the help of the capacitor, we can define the triangular shape of the signal; charging the capacitor defines the rise of the signal while discharging defines the fall of the triangular wave. This amplifier has a heat sink that does not get hot easily as compared to the class AB amplifier.

Schematic Diagram:

I have used the Altium designer to design my schematic diagram. First of all, I have created the symbols and footprints of all the components then I have designed my schematic. I have uploaded my schematic file online on Inventhub for the users who want to implement my design. They can go to the provided link and can view or download my design easily. I can also view the changes I have made in my design by going to the ‘view changes’ tab. I can also collaborate with the people, they can comment on my design and can give suggestions to improve my design further.

PCB Board Design:

I have converted my schematic file to the PCB file in Altium, where I can create connections on the board, define the shape of the board, arrange the components on the board, and can view my PCB in 3D view. I have uploaded my PCB file on Inventhub, where I can view my boards in different layers and can focus on a specific layer by disabling the other layers. Users and manufacturers can easily view or download my design for the implementation. Users do not need to design the symbols and footprints, they can download those parts from my components management library on Inventhub. This can help in reducing the errors in the design.

I have created a release file of the project on Inventhub which contains all the design files in a ZIP file format. For the fabrication, I do not need to visit the manufacturer instead I can send him the release file of the project. He can easily download the files and can fabricate my PCB board.

Project History:

To create a backup of my edits in the design, I have uploaded different revisions of my design on Inventhub. This contains the edits of my design at different stages. If I want to get back the specific change I have made in my design, I can go to the revision and can select that particular file and can download it to reuse it as my current design.

Bill of Materials:

After the fabrication of the board, I created a list of components on Inventhub which contains the details of the manufacturer, supplier, manufacturer part number, pricing, and quantity. By just putting these details in the BOM file on Inventhub, it has calculated the total cost of the design automatically using the supply chain option. I can also view the datasheet of the component and can view its 3D model. For this project, our cost is almost $17.23 which is reasonable.

Instead of visiting the component provider, I can send him this BOM file, he can download it in CSV file format and can deliver my components as per my design requirements.

Feel free to ask any query at arshmah@inventhub.io