Class D audio amplifier working principle diagram + design components list

This article mainly shares: Class D amplifiers, advantages and disadvantages of Class D amplifiers, Class D amplifier principles, Class D amplifier circuit diagrams, Class D amplifier design, and Class D amplifier testing.

1. Class D Amplifier Tutorial

What is a Class D audio amplifier? The simplest way to say it is that a Class D audio amplifier is a switching amplifier. In order to understand the working principle of a Class D audio amplifier, we need to understand the function of a Class D audio amplifier and how the switching signal is generated. The following block diagram is given to help you understand.

Class D audio amplifier working principle diagram

What about Class D amplifiers?

Class D amplifiers are highly efficient. Class D audio amplifiers can be as efficient as 90-95% compared to Class A, B, and AB amplifiers, which have a maximum efficiency of 60-65%, because they operate in the active region and exhibit low power losses, as you can see if you multiply the collector-emitter voltage by the current.

3. Class D Amplifier Principle

Now, back to the simplified functional block diagram of a Class D audio amplifier.

Class D Amplifier Principle

What you see at the non-inverting end, there is the audio input; at the inverting end, there is the high frequency triangle signal.

At this time, when the voltage of the input audio signal is greater than the voltage of the triangle wave, the output of the comparator becomes high, and when the signal is low, the output is low. With this setup, we simply modulate the input audio signal with a high-frequency carrier signal, and then connect it to the MOSFET gate driver IC. As the name suggests, the driver is used to drive the gate side and low side of the two MOSFETs at once.

At the output, we get a strong high frequency square wave, which we pass through a low pass filter to get our final audio signal.

Class D amplifier working principle diagram

Components Required for Class D Amplifier Design

Now that we know the basics of Class D amplifiers, we can DIY a Class D amplifier. This is a relatively simple test project, and the components are relatively common. You can buy most of the components directly online. The following is a list of components with pictures.

Parts List for Building a Class D Power Amplifier

Parts List for Building a Class D Power Amplifier:

Figure 1. Parts list for building a Class D power amplifier

5. Class D audio amplifier circuit diagram

The circuit diagram of the Class D amplifier circuit is shown below:

Class D amplifier circuit diagram

6. How to use Class D amplifier

Here we mainly talk about each main functional module of the Class D audio amplifier and explain the working principle of each module.

1. Input voltage regulator

Input voltage regulator

First regulate the input voltage using 5V regulator LM7805 and 12 volt regulator LM7812. This is very important because we are going to power the circuit using 13.5V DC adapter and to power NE555 and IR2110 ICs, 5V and 12V power supplies are required.

2. Triangle wave generator with 555 astable multivibrator:

Triangle wave generator with 555 astable multivibrator

As can be seen from the figure below, we use a 555 timer with a 2.2K resistor to generate a 260KHz triangle signal.

3. Modulation circuit:

Modulation Circuit

As you can see from the above figure, we have used a simple LM358 op-amp to modulate the input audio signal. Speaking of the input audio signal, we have used two 10K input resistors to get the audio signal, and since we are using a single supply, we have connected a potentiometer to offset the zero signal present in the input audio.

When the value of the input audio signal is greater than the input triangle wave, the output of this comparator will be high and at the output, we will get the modulated square wave which is then fed to the MOSFET gate driver IC.

4. IR2110 MOSFET gate driver IC:

IR2110 MOSFET Gate Driver IC

We have used a MOSFET gate driver IC to drive the MOSFET properly. All the necessary circuits are placed as suggested in the IR2110 IC datasheet.

To work properly, this IC requires an inverted signal of the input signal, so we use a BF200 high frequency transistor to generate an inverted square wave of the input signal.

5. MOSFET output stage:

MOSFET Output Stage

As you can see from the above diagram, we have the MOSFET output stage which is also the main output driver, and since we are dealing with high frequencies and inductances, there are always transients involved, so we use some UF4007 as flyback diodes to prevent the MOSFET from getting damaged.

6. LC low-pass filter:

LC Low Pass Filter

The output of the MOSFET driver stage is a high frequency square wave, which is definitely not suitable for driving loads such as speakers.

To prevent it, we use a 26uH ​​inductor and a 1uF non-polarized capacitor to make a low pass filter, denoted as C11. This is the simple circuit function.

7. Testing Class D Amplifier Circuits

Testing Class D Amplifier Circuits

As you can see from the above picture, a 12V power adapter is used to power the circuit, which sends out a voltage slightly higher than 12V, 13.5V to be exact, which is perfect for our onboard LM7812 voltage regulator.

The load used was a 4 Ω, 5 W speaker. For audio input, I used a laptop with a 3.5 mm long audio jack.

When the circuit is powered up, there is no noticeable hum like other types of amplifiers, but this circuit does have clipping issues at higher input levels, so this circuit has a lot of room for improvement. When driving moderately low loads, the MOSFET did not get hot at all, so for these tests it did not require any heat sink.

8. Further Enhancement

This class D amplifier circuit is a simple prototype and has a lot of room for improvement. The main problem with this circuit is the sampling technique, which needs to be improved. In order to reduce clipping of the amplifier, the appropriate inductor and capacitor values ​​need to be calculated to get a perfect low pass filter stage. As always, the circuit can be made on a PCB for better performance. A protection circuit can be added to protect the circuit from overheating or short circuits.