-
-
-
Solutions
-
-
language
Delve deeply and work diligently to achieve new heights
All colleagues unite and focus their efforts to write a new chapter of developmentAnalysis of the Causes of Abnormal Noise in Switching Power Supply Transformers
所属分类： Industry News
发布时间：2020-06-12
The whine of a transformer is primarily caused by low-frequency oscillations in its magnetizing current, which induce the magnetic domains in the core to vibrate at that low frequency, generating mechanical vibrations that, in turn, set the surrounding air into motion. Since the human ear can perceive frequencies roughly between 20 Hz and 20 kHz, if these air vibrations fall within this range, they are ultimately transmitted to the ear and heard.
The main causes of acoustic noise in switch-mode power supply transformers fall into four categories: manufacturing‑process issues, loop‑related problems, core‑material defects, and… Switching power supply The load issues will be analyzed one by one below.
1. The transformer core issue
When the transformer core saturates, the current in the windings increases, causing the transformer to heat up and generating self‑excited oscillations. The oscillations of the windings induce vibrations in the surrounding air, producing audible noise.
2. Load issues in switch-mode power supplies
2.1 The transformer is operating under severe overload conditions, with an imminent risk of burnout at any moment—this is the root cause of the “screaming” that many power supplies exhibit before failing.
2.2 Under no-load or light-load conditions, switch-mode power supplies may exhibit oscillation at certain operating points, manifesting as transformer hum and output instability.
This phenomenon occurs because, under no‑load or light‑load conditions, the switch’s turn‑on transient duration is excessively long, leading to an excessive output energy and a significant voltage overshoot. As a result, it takes a prolonged period for the voltage to return to its normal level, necessitating that the switch remain off for a certain interval. Consequently, the switch operates in an intermittent mode, causing the transformer to vibrate at a lower frequency—either with regular, intermittent full‑off cycles or with a frequency characterized by abrupt changes in duty cycle.
3. Process-related issues of transformers
3.1. An improperly tightened coil winding may also cause noise.
3.2 When the magnetic core assembly contains an air gap, high-frequency operation can cause the air to vibrate, producing audible noise (transformers that have undergone full vacuum impregnation typically do not generate sound).
3.3 Insufficient varnish impregnation and baking result in an unstable magnetic core, causing mechanical vibration and noise.
3.4 The air gap length is inappropriate, causing the transformer to operate unstably and produce noise.
4. Loop issues in transformers
The loop problem in transformers refers to oscillations occurring in the transformer’s feedback loop, which can cause the transformer to emit a whining noise.
4.1 Component quality issues in the circuit—such as insufficient capacitance in the input filter capacitor, poor‑quality fast‑recovery rectifier diodes at the output, substandard power MOSFETs, or defective high‑voltage capacitors or diodes in the RCD snubber circuit—can all trigger oscillations and produce audible noise.
4.2 Improper PCB routing can cause interference, leading to oscillation and resulting in noise.
4.3 Improper setting of feedback loop parameters can lead to loop instability, resulting in oscillations and audible noise.