Don't worry about the mini house boom anymore! - Have you heard of a small inductor for a Class D amplifier for a car?
Recently, when you turn on your TV or browse the web, you're likely to come across a lot of news about the mini-house trend. The idea that "smaller is better" has taken hold in many industries, and the mobile phone sector is no exception—manufacturers are now focusing on producing compact, lightweight devices.
This same philosophy is now making its way into the automotive industry, particularly in the field of Class D audio amplifiers. In this blog post, I’ll explore how using smaller inductors can help create more efficient and compact Class D amplifiers for infotainment systems.
Background
Class D audio amplifiers used in vehicles require an output filter to ensure clean audio signals. This filter typically consists of an inductor and a capacitor, commonly referred to as an LC filter. Choosing the right inductor value is essential for achieving good audio performance, efficiency, electromagnetic compatibility (EMC), and cost-effectiveness, especially in applications like main audio units or external amplifiers.
The bridged load configuration shown in Figure 1 is a common setup where the speaker is connected between two amplifier outputs. This means that each channel in a vehicle’s audio system usually requires two inductors.
Figure 1: Class D amplifier bridged load circuit
Why Small Inductors Matter
Modern cars are packed with more electronics than ever before. However, space is limited, and car manufacturers are pushing suppliers to make components smaller and lighter. This not only helps with design flexibility but also contributes to overall vehicle weight reduction, which improves fuel efficiency.
In a typical car radio with four channels (two front and two rear speakers), eight inductors are needed—one for each channel. These inductors take up significant space on the PCB and add to the system's overall weight. Reducing their size and weight is therefore a key priority in modern infotainment system design.
Inductor Size vs. Amplifier Switching Frequency
The inductance value required for an LC filter in a Class D amplifier depends largely on the switching frequency. At lower frequencies, such as 400 kHz, larger inductors are necessary. For example, a 400 kHz amplifier might use 10 μH or 8.2 μH inductors. However, at higher frequencies, like 2.1 MHz (as seen in TI’s TAS6424-Q1), smaller inductors—such as 3.3 μH to 3.6 μH—can be used without compromising performance.
Figure 2: Comparison of inductor size and switching frequency
What Affects Inductor Weight?
The weight difference between an 8.2 μH and a 3.3 μH inductor comes down to the materials used. Larger inductors require more copper wire and heavier core materials to handle the current and maintain the required inductance. In a four-channel system, this adds up quickly. As shown in Figure 3, switching to a higher frequency system can significantly reduce both the weight and size of the inductors.
Figure 3: Inductor weight comparison for a four-channel amplifier
New Metal Alloy Inductors Enable Smaller Designs
Traditional inductors at 400 kHz use copper windings and ferrite cores. But with higher switching frequencies, new metal alloy cores allow for much smaller and lighter inductors. These advanced inductors not only save space but also reduce the overall weight of the system. As shown in Figure 4, they provide a more compact solution for multi-channel amplifiers.
Figure 4: Small Metal Alloy Inductors for a Quad Amplifier
Conclusion
Class D amplifiers with higher switching frequencies, like the 2.1 MHz TAS6424-Q1, are shaping the future of automotive audio systems. These designs not only improve performance but also push the inductor industry toward smaller, lighter solutions. As the demand for compact and efficient infotainment systems grows, high-frequency Class D amplifiers will play a crucial role in meeting these challenges.
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