AC Adapter Whining Noise: Causes and Solutions

Understanding Whining Noises from AC Adapters and Power Supplies

Typically, AC adapters and power supplies operate silently. However, a whining sound emanating from one can understandably cause concern. Is this a sign of a problem? This article addresses a reader’s inquiry regarding this issue.

The Source of the Noise

The following explanation is based on a question posed and answered within the SuperUser community. SuperUser is a segment of Stack Exchange, a network of question-and-answer websites maintained by its users.

A whining noise often originates from the components within the power supply vibrating at a specific frequency. This is particularly common in switching power supplies.

Why Does This Happen?

• Component Vibration: Certain components, like transformers and inductors, can physically vibrate when electricity passes through them.
• Frequency Matching: If the vibration frequency coincides with an audible range, a whining sound is produced.
• Load Sensitivity: The intensity of the whine can fluctuate depending on the electrical load placed on the power supply.

While often harmless, the noise can indicate stress on the components. It's important to monitor the situation.

Is It a Cause for Concern?

Generally, a mild whine isn't immediately indicative of failure. However, a progressively louder whine, or one accompanied by other symptoms, warrants investigation.

Potential Issues to Watch For:

• Overheating
• Reduced performance of the connected device
• Unusual smells

If you observe any of these, discontinue use and consider replacing the power supply or AC adapter.

Further Information

The original discussion and further insights can be found on SuperUser. The image accompanying this explanation is credited to Bart Everson (Flickr).

Understanding the Whining Noise in Power Supplies

A SuperUser user, Rishat Muhametshin, has inquired about the cause of a whining sound emanating from various AC adapters and power supplies. This issue is observed across a range of devices, from small 5V/1A USB chargers to larger laptop adapters and desktop PSUs.

The Phenomenon Explained

The whining noise is frequently noticed when these power supplies operate without a connected load, or with a partially charged device. Interestingly, the sound ceases when a device requiring more power is connected.

The Root Cause: Magnetostriction

The primary reason for this audible whine is a phenomenon called magnetostriction. This occurs within the power supply’s transformer.

Transformers utilize laminated steel cores to efficiently transfer energy. However, these laminations can subtly change shape when subjected to a magnetic field.

How Magnetostriction Creates Noise

This shape change, though minuscule, happens at the frequency of the alternating current (AC) – typically 50 or 60 Hz. The rapid expansion and contraction of the laminations generate vibrations.

These vibrations are then transmitted to the transformer’s housing, which acts as a sounding board, amplifying the sound into the whining noise we perceive.

Why Some Units are Quieter

Not all power supplies exhibit this behavior due to several factors. The quality of the materials used in the transformer core plays a significant role.

• Core Material: Higher-quality silicon steel laminations are less prone to magnetostriction.
• Tightness of Lamination: A more tightly packed core reduces the space for vibrations.
• Potting/Encapsulation: Some power supplies employ potting compounds or encapsulation to dampen vibrations.
• Load Dependency: The noise is often more pronounced at lighter loads because the magnetic flux density is higher.

Can the Noise Be Suppressed?

While eliminating the noise entirely can be difficult, several approaches can help reduce it.

Adding a minimal load to the power supply can sometimes diminish the whine. This is because a small current draw alters the magnetic flux and reduces magnetostriction.

Physically damping the transformer itself, if accessible, might also offer some relief. However, this should only be attempted by someone experienced in electronics repair, as it could void warranties or create safety hazards.

Ultimately, the presence of this whining noise is generally a sign of a functioning, though not necessarily optimized, power supply. It rarely indicates an imminent failure.

Understanding AC Adapter and Power Supply Whining Noises

The source of the high-pitched whining sound emanating from some power conversion devices is explained by contributions from SuperUser users DragonLord and Daniel R Hicks.

The Role of Coils and Electromagnetism

Many power conversion devices, including transformers and inductors, rely on electromagnetism to convert alternating current (AC) mains power into low-voltage direct current (DC) power.

The fluctuating magnetic fields produced by these components can induce physical vibrations at high frequencies, which manifests as an audible, whining noise.

Switched-Mode Power Supplies (SMPS) and Frequency

Modern AC adapters predominantly utilize switched-mode power supplies (SMPS). The internal switching frequency within an SMPS isn't constant.

• It typically operates at a lower frequency when there's minimal load.
• As the load increases, the frequency rises, up to a design-specific limit.

This lower, no-load frequency often falls within the range of human hearing.

PWM and Coil Vibration

In situations with low or no load, the Pulse Width Modulation (PWM) employed for voltage regulation at the inverter stage operates with a low duty cycle.

This results in a "spikey" output profile, increasing the susceptibility of coils to vibration, and the transformer itself can also vibrate. These factors combined can generate audible noise, particularly in less expensive units lacking adequate noise suppression.

Load and Sub-Harmonic Frequencies

A properly functioning SMPS, when under load, should operate at a frequency exceeding the human hearing range – generally 50 KHz or higher.

However, a poorly designed or defective power supply can still produce noise even under load, as the coils may vibrate due to electrical stress at a sub-harmonic frequency.

Mitigation Techniques: Glue and its Application

Manufacturers sometimes apply a glue-like substance to coils within electronic devices to dampen vibrations and reduce noise generation.

Users have successfully replicated this by applying glue from a glue gun to coils in components like PC motherboards, graphics cards, and power supplies.

However, applying glue to small wall chargers is generally not recommended due to the risk of damage or exposure to hazardous voltages.