Do Switching Power Supplies Make Noise? A Deep Dive into Power Supply Acoustics

Yes, switching power supplies (SMPS) absolutely can and often do make noise. The noise can range from barely audible to quite annoying, and it stems from various sources within the power supply itself. Understanding these sources and what to do about them is crucial for both designers and users of electronic equipment. The nature of the noise, its loudness, and its frequency can provide valuable clues about the health and operating conditions of the power supply.

Understanding the Sources of Noise in Switching Power Supplies

Switching power supplies are inherently noisy due to their method of operation. Unlike linear power supplies, which regulate voltage by dissipating excess power as heat, SMPS rapidly switch current on and off to regulate voltage. This switching action generates electromagnetic interference (EMI), which can manifest as audible noise. Let’s break down the primary noise sources:

Magnetic Component Noise

This is probably the most common and noticeable type of noise. Transformers, inductors, and other magnetic components vibrate mechanically due to the alternating magnetic fields they generate. This vibration can be amplified by the surrounding structure, resulting in audible noise. Several factors contribute to this:

• Switching Frequency: If the switching frequency or its harmonics fall within the audible range (20 Hz to 20 kHz), the vibration becomes audible.
• Loose Windings: Loose windings in coils and transformers can vibrate against each other, creating buzzing or whining sounds.
• Core Saturation: If the magnetic core becomes saturated, it can lead to non-linear behavior and increased vibration.
• Magnetostriction: This phenomenon involves the change in shape of a ferromagnetic material (like the transformer core) when subjected to a magnetic field. This minute change, occurring at the switching frequency, can generate audible noise.

Capacitor Noise

While less common than magnetic component noise, capacitors can also contribute to audible sounds. Ceramic capacitors, in particular, are prone to a phenomenon called piezoelectricity, where they change shape slightly when subjected to voltage changes. If these voltage changes occur at audible frequencies, the capacitor can vibrate and produce a high-pitched whine.

Fan Noise

Many switching power supplies, especially those used in computers and high-power applications, incorporate fans for cooling. Fan noise is generally broadband (covering a range of frequencies) and can be a significant contributor to the overall noise level of the power supply. The fan’s speed, bearing quality, and design will influence the amount of noise it produces.

Electrical Noise

Switching transients, high-frequency oscillations, and other forms of electrical noise can also contribute to audible sounds, although indirectly. These electrical disturbances can induce vibrations in other components, such as the chassis or enclosure, which then radiate sound.

Reducing Noise in Switching Power Supplies

Reducing noise in switching power supplies is a multifaceted challenge. Here’s a look at some common techniques:

Component Selection

• Low-Noise Magnetic Components: Using high-quality transformers and inductors with tightly wound coils and well-laminated cores can minimize vibration.
• Solid Polymer Capacitors: Replacing ceramic capacitors with solid polymer capacitors can reduce piezoelectric noise.
• Quiet Fans: Selecting fans with optimized blade designs and low-noise bearings can significantly reduce fan noise.

Filtering

• Input Filters: Filters can reduce noise entering the power supply from the AC line.
• Output Filters: Filters can reduce noise at the output, preventing it from affecting the connected load.
• Common-Mode Chokes: These components help to suppress common-mode noise, which is a type of EMI.

Shielding

• Enclosures: Enclosing the power supply in a metal enclosure can block radiated EMI and reduce audible noise.
• Shielding Cans: Shielding individual components, such as transformers, can further reduce EMI and noise.

Damping

• Damping Materials: Applying damping materials to vibrating components can reduce the amplitude of their vibrations and the resulting noise.
• Glue/Varnish: Applying insulating varnish or coil lacquer to coils can help secure them and prevent vibrations.

Circuit Design

• Soft Switching Techniques: Implementing soft switching techniques can reduce switching transients and EMI.
• Frequency Shifting: Slightly varying the switching frequency can spread the noise over a wider range, making it less noticeable.

Addressing Specific Noise Issues

• Buzzing: Often related to loose windings in transformers. Try applying varnish or epoxy to secure the windings.
• Whining: Can be caused by ceramic capacitors or high-frequency oscillations. Try replacing the capacitors or improving filtering.
• Clicking: May indicate a relay switching. This is often normal, but repetitive loud clicking could indicate a problem.

The Importance of Noise Reduction

Minimizing noise in switching power supplies is not just about creating a more pleasant user experience. Excessive noise can also indicate underlying problems with the power supply, such as component stress or improper design. Addressing these issues can improve the reliability and longevity of the power supply and the equipment it powers. Moreover, reducing EMI is crucial for ensuring that the power supply does not interfere with other electronic devices. The concepts of circuit design and noise reduction can be better understood through interactive experiences, such as games and simulations. The Games Learning Society offers resources that explore these topics in engaging and effective ways; visit GamesLearningSociety.org for more information.

Frequently Asked Questions (FAQs)

1. Is it normal for a power supply to buzz?

A slight buzzing sound from a power supply is sometimes normal, especially with older or lower-quality units. This is often due to the magnetic components vibrating. However, excessive buzzing, or a sudden increase in buzzing, could indicate a problem.

2. What causes a power supply to hum?

Electric hum around transformers is usually caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction within the transformer core can also be a source of vibration.

3. Why does my PSU make a clicking sound?

Most power supplies have an inrush current bypass relay that makes a click noise when the PC turns on and off. This is generally normal. However, loud, repetitive clicking after the PC is on could indicate a failing relay or another problem.

4. How do you reduce the noise of a switching power supply?

Noise reduction involves a combination of strategies, including using low-noise components, implementing filtering and shielding, and applying damping materials. Circuit design techniques like soft switching can also help.

5. What is the common-mode noise of a power supply?

Common-mode noise in AC power is the noise signal between the neutral and ground conductors. This is different from normal-mode noise, which is between the line (hot) and neutral conductors.

6. How do I get rid of high-frequency noise?

High-frequency noise can be reduced using low-pass filters, which attenuate frequencies above a certain cutoff point. Careful component selection and shielding can also help.

7. Can the human ear hear 50Hz?

Yes, the human ear can typically hear sounds in the range of 20 Hz to 20,000 Hz. A 50 Hz hum is well within this range and is easily audible.

8. What is the annoying frequency noise?

Low-frequency noise (10Hz to 200Hz) can be particularly annoying to some people. Sounds in the higher-frequency range of around 2,000 to 5,000 Hz were rated as most unpleasant.

9. What does high-frequency noise sound like?

High-frequency noise can sound like a whine, hiss, or screech. Examples include birds chirping, sirens wailing, or cymbals crashing.

10. How do you stop high-pitched noise from electronics?

Paint insulating varnish or coil lacquer on the specific coils that you suspect are causing the high-pitched noise. Once it dries, the liquid will form a thick, protective barrier around the coils that should help reduce or even completely stop the coil whine.

11. How do you reduce MOSFET switching noise?

By inserting a resistor between the gate and the gate driver of the high-side MOSFET, gate charge is limited, and rising and falling of the high-side MOSFET are made gradual or “blunted”, so to speak, to reduce noise during both turn-on and turn-off.

12. How do you measure power supply noise?

The main tool for measuring power regulator noise is an oscilloscope, and possibly a spectrum analyzer if you want to look at the noise power spectrum.

13. How can I tell if PSU is bad?

Signs of a failing PSU include:

• Power-on failures
• Spontaneous rebooting
• Intermittent lockups
• Hard drive and fan failures
• Overheating
• Small brownouts

14. Is a noisy PSU bad?

A noisy PSU is not necessarily bad, but it can be a warning sign. If the noise is excessive or accompanied by other symptoms, it’s worth investigating.

15. Why do I suddenly hear a high-pitched sound?

A sudden high-pitched sound, especially if it’s constant, could be related to tinnitus or other auditory issues. It’s best to consult a medical professional if this persists. If it is only present when electronics are on, then the source is more likely the electronic device itself.

By understanding the sources of noise in switching power supplies and implementing appropriate mitigation techniques, designers and users can create quieter, more reliable, and more enjoyable electronic devices.