As I get older, I suspect I’m gradually getting deafer. My hearing was pretty sharp during my teenage years but these days, I miss out on conversations and need to frequently ask people to repeat themselves. Perhaps my hearing ability is deteriorating due to age; however, when I hear static noise creeping out of an amplifier, I know to trust my ears.
In electronics, the power supply of audio circuits can mean the difference between perfect audio quality and irritating background noise. In certain cases, you can immediately hear noise as you turn on the amplifier; in other situations, these noises are detected only by the most sensitive listeners. Either way, unwanted background noise robs users of the satisfaction of beautiful audio.
Types of Audio Power Supply Design
In audio design, you’ll come across three types of power supply design. The first type of design involves a simple unregulated power supply that only requires a transformer to step down the incoming voltage, along with a couple of passive components. While this type of design provides the easiest way to build a power supply, it causes a ripple in the DC voltage and affects audio circuit performance.
The second type of power supply design involves a linear regulated voltage supply that provides a cleaner voltage source than unregulated ones. Despite this advantage, linear regulated voltage supply designs can be expensive and more complex to design. Heat dissipation is also a prominent issue, as the voltage is dropped over a voltage regulator. Furthermore, regulated supply designs can also be unstable in high-frequency ranges.
The best type of audio power design is perhaps the third type: switch mode power supply. Compared to the previous two design types, it offers the most advantages, like the absence of a heavy transformer. It can also support a wide range of input voltages. However, the switch mode power supply is also a common source of high-frequency noise in the audio output.
Tips for Audio Power Supply Circuit Design
While the ultimate choice of the power supply type depends on factors like cost and design complexities, certain design techniques are essential to reduce interference on the audio output and prolong the lifespan of the power supply itself.
With smooth audio, the right power supply design makes users smile.
1. Inrush Current Limiting Circuit
Ever experience water splashing all over you as you turn it on abruptly? When the power supply is suddenly turned on, inrush current has a similar effect. The sudden rush of current that surpasses the tolerated limit of the power supply may eventually damage components.
To mitigate the damaging effects of inrush current, it is important to add a current limiting circuit to the design. A simple circuit consists of resistors and a Zener diode to clamp and reduce the inrush current. In some designs, a relay is also included to short-circuit the input when the rising current breaches the limit.
2. Low Pass Filter
I usually avoid engaging in serious conversations at crowded events, as the noise level makes it impossible to hear every other word. In audio power supply design, high-frequency noise can couple itself to the audio output, turning pleasant music into irritating noises.
A low-pass filter using the correct value of capacitors and inductors prevents any noises above 1 kHz from coupling into audio components. This dramatically improves sound performance.
Use a low pass filter to keep out high-frequency noise.
3. Thermal Management
Heat dissipation issues are common in any power supply design, including those that drive audio application. When nothing is done to disperse the heat, it accumulates and shortens the lifespan of surrounding components. While FR-4 is a commonly used substrate for PCB, aluminum PCBs have a much better heat dissipation rate.
Besides considering the type of PCB to use, you need to apply proper heat management techniques to the PCB itself. For example, onboard heatsinks and thermal vias help prevent heat build-up at a single point. With flexible design software like Altium Designer, you can easily place thermal vias on the PCB.
Need more tips on audio power supply circuit design? Talk to the experts at Altium today.
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