Battery line capacitors (12 V power supply line)
1) Capacitor mounting locations
These capacitors are mounted in five different circuits (circuits A to E), such as the CPU circuit.
We evaluated acoustic noise in the capacitors in the battery line indicated in pink, and took measures against it.
3) Replacement evaluation results
|The data shown below are reference values obtained through our own evaluations. The sound pressure level reduction effects differ depending on the circuit board shape, parts mounting state, and other conditions. Note that effects are not guaranteed for all cases.
The sound pressure level differs depending on the operating mode, so acoustic noise was evaluated and solutions were proposed for four operating modes that have a high sound pressure level: camera start-up, sleep mode, video playback (LCD screen maximum luminance), and standby screen.
※All evaluations were performed in the fully charged state with the AC adapter connected.
The sound pressure level could be reduced as shown below by replacing all of the battery line capacitors with low acoustic noise “KRM” capacitors.
The detailed results for each operating mode are shown below.
＜Detailed results of replacement (1/4) ＞ Camera start-up
＜Detailed results of replacement (2/4) ＞ Video playback
＜Detailed results of replacement (3/4) ＞ Sleep mode
＜Detailed results of replacement (4/4) ＞ Standby screen
Change in sound pressure level due to replacement with low acoustic noise capacitors (KRM) circuit by circuit (1/2)
The battery line capacitors (area enclosed in the pink frame) are located in the same power line before splitting into each circuit at the DC-DC converter, so they all experience approximately the same voltage fluctuation.
The capacitors in this battery line were replaced with low acoustic noise capacitors circuit by circuit, and the effects were evaluated.
Change in sound pressure level due to replacement with low acoustic noise capacitors (KRM) circuit by circuit (2/2)
The battery line capacitors shown in the figure above were replaced from normal capacitors (GRM) to low acoustic noise capacitors (KRM) in order, from circuit [A] to circuit [E].
The sound pressure level decreased gradually as the number of capacitors replaced with KRM series capacitors increased.
The sound pressure level can be reduced even further by replacing not just some, but all of the capacitors with low acoustic noise capacitors as a solution to suppress acoustic noise in the battery line.
1）Mechanism of acoustic noise
Acoustic noise is produced by capacitors as follows. When an AC electric field is applied to a capacitor made of material with a high dielectric constant, the capacitor deforms and vibrates. This vibrates the circuit board, which results in the issue of “unpleasant noise” when the vibration cycle is in the audible frequency range (20 Hz to 20 kHz).
2) Method of evaluating acoustic noise
The sound pressure level is measured, and the acoustic noise is quantified.
The voltage fluctuation and the circuit board displacement are measured and evaluated, and the causes of the acoustic noise are investigated.
The current capacitors are then replaced with low acoustic noise capacitors, and the sound pressure level is measured and evaluated to confirm the effects.
3) Capacitors and operating modes that easily produce acoustic noise in a laptop computer
Capacitors are used in the battery line (DC-DC converter primary side) of a laptop computer.
This battery line is typically high voltage and supplies power to circuits that have high power consumption. This means that voltage fluctuation easily occurs, which results in operating conditions in which capacitors easily produce acoustic noise.
In addition, operating modes in which acoustic noise easily occurs include sleep mode, camera start-up, PWM dimming of the LCD backlight, and video playback.
4) Evaluation of replacement in a laptop computer
When the operating mode is changed, the internal operation of the laptop computer also changes, so it is necessary to perform evaluation in each operation mode in which acoustic noise easily occurs.
When multiple ceramic capacitors are used in a battery line (DC-DC converter primary side), the sound pressure level can be suppressed even further by using low acoustic noise capacitors for not just some, but all of the battery line capacitors.
Introduction of low acoustic noise capacitors
＜Factors influencing acoustic noise, and solutions＞
When acoustic noise due to the influence of ceramic capacitors becomes an issue, Murata proposes solutions to suppress this acoustic noise, such as the use of low acoustic noise capacitors or modification of the component layout, depending on the factors influencing the acoustic noise.