The following article is from Murata China Author Murata

In wireless chargers, film capacitors are sometimes used in the resonant circuit. MLCCs are more suitable for miniaturization and can help reduce mounting area. Additionally, MLCCs generally offer advantages in terms of device surface temperature control and power conversion efficiency. Here, we present an evaluation conducted by Murata on replacing film capacitors with multilayer ceramic capacitors (MLCCs).

Evaluation Subject

We conducted a replacement evaluation using a commercially available wireless charger. In the photo below, the red circles indicate the film capacitors installed as resonant capacitors in the original design.

Replacement Proposal

In the original design (shown above), the film capacitor specifications are 7.3 × 6.5mm, 0.33μF, 63V. The Murata replacement proposal is shown in the image below. The replacement product is GRM3195C2A104JA01 (1206, C0G, 0.1μF, 100V).

Proposal Evaluation

To evaluate the results after replacing the film capacitor, we verified the following characteristics (evaluation items) during charging before and after the capacitor replacement:

1.     Capacitor surface temperature rise

2.     Power conversion efficiency

Measuring Capacitor Surface Temperature
The conditions for measuring the capacitor surface temperature were set as follows:

·       Operating Environment: When using the wireless charger

·       Measurement Environment: Placing the wireless charger inside a wind shield for measurement

·       Measurement Equipment: Infrared thermal camera

·       Room Temperature During Measurement:

o   When measuring the film capacitor: 26.0°C

o   When measuring the MLCC: 24.5°C

o    

Film Capacitor: 7.3×6.5mm, 0.33μF, 63V
Peak Temperature: Approximately 57.0°C

MLCC: GRM3195C2A104JA01 (1206, C0G, 0.1μF, 100V) × 4 pieces
Peak Temperature: Approximately 34.6°C

This measurement confirmed a difference in surface temperature rise exceeding 20°C between the film capacitor and the MLCC.
Furthermore, the ESR (Equivalent Series Resistance) of the MLCC is lower than that of the film capacitor, resulting in better temperature rise control.

ESR Curve Comparison: Film Capacitor vs. MLCC

Power Conversion Efficiency
Using the capacitors mentioned above, we evaluated the power conversion efficiency during charging. This evaluation confirmed that the power conversion efficiency of the MLCC is more than 2% better than that of the film capacitor.

Power Conversion Efficiency Comparison: Film Capacitor vs. MLCC

Summary
We replaced the film capacitors in the original wireless charger design with MLCCs and verified the characteristics of capacitor surface temperature rise and power conversion efficiency during charging. The results show that the MLCC solution offers prominent advantages in the following three aspects:

·       Capacitor Surface Temperature Rise: The MLCC's ESR (Equivalent Series Resistance) was confirmed to be lower than that of the film capacitor, resulting in a difference in surface temperature rise exceeding 20°C.

·

·       Power Conversion Efficiency: The MLCC's power conversion efficiency was confirmed to be more than 2% better than that of the film capacitor.

·       Space Advantage: In a direct comparison between an MLCC and a film capacitor, the MLCC is more suitable for miniaturization and can help reduce mounting area.
The alternative solution uses four MLCCs from Murata Manufacturing Co., Ltd.: GRM3195C2A104JA01 (1206, C0G, 0.1μF, 100V).

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