JPH088188B2 - Monolithic ceramic capacitors - Google Patents

Description

TECHNICAL FIELD The present invention relates to a monolithic ceramic capacitor, and more particularly to a monolithic ceramic capacitor for a power supply suitable for a high frequency switching power supply.

[Conventional technology]

The switching frequency of the switching power supply has been increasing year by year, and the mechanical resonance frequency due to the electrostrictive effect of the multilayer ceramic capacitor for power supply, which has not been a problem in the past, has been highlighted. In conclusion, when the switching frequency of the power supply and the mechanical resonance frequency of the monolithic ceramic capacitor for power supply are close or match, there is a phenomenon that the power supply function is impaired. This depends largely on the external dimensions of the capacitor, and the mechanical resonance frequency due to the electrostrictive effect of the monolithic ceramic capacitor of the size conventionally used as standard is shown in Table 1.

As shown in Table 1, the length of the monolithic ceramic capacitor,
There are primary resonance frequencies corresponding to the width and thickness, and secondary and tertiary resonance points that are integral multiples of each frequency are observed. For example, in the case of sample No. 2, 330kHz, 430kHz, 660kHz, 8
It is 60kHz, etc., especially the secondary resonance point becomes a problem, and in the case of the switching frequency of the power supply, for example 460kHz, if the mechanical resonance point of the capacitor is within the range of ± 100kHz, the power supply becomes unstable. It is easy to cause troubles such as emission of noise radio waves. Especially for input side filters of power supply,
Also, it becomes a problem with the monolithic ceramic capacitor for smoothing the output side.

[Problems to be Solved by the Invention]

Speaking of the example of the sample in Table 1, No. 1 and No. 2 are 460kHz ± 10 when the switching frequency of the power supply is 460kHz, for example.
This is a problem because the mechanical resonance point of the capacitor exists within the range of 0kHz (360kHz to 560kHz).

The problem to be solved is the switching frequency of the power supply ± 100k
There should be no mechanical resonances of the capacitor in the Hz range, and the number of such resonances should be as low as possible.

[Means for solving the problem]

It can be seen from the measured values in Table 1 that there is an inverse relationship between each dimension of the multilayer ceramic capacitor chip and the mechanical resonance frequency of this capacitor. For example, if the length dimension is doubled, the resonance frequency Becomes # times. Therefore,
It was found that the number of mechanical resonance points of the capacitor can be reduced and the resonance point can be made outside the switching frequency ± 100kHz of the power supply by properly devising the chip size of the multilayer ceramic capacitor.

That is, the ratio of the length, width, and thickness of the external dimensions of the chip body is 0.5 ± 20% when the length is 1, and the thickness is
A chip type characterized by 0.25 ± 20% and an exterior type laminated ceramic capacitor using this chip.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 is an external view of a chip monolithic ceramic capacitor for high frequency power supplies according to an embodiment of the present invention. FIG. 2 is a perspective view of a resin-coated monolithic ceramic capacitor with lead electrodes for a high frequency power source according to an embodiment of the present invention. In FIG. 1, 1 is a chip body, 2 is an external electrode, the length of the chip body,
The width and thickness are in the ratio of 1 to # ± 20% to $ ± 20%. Also in FIG. 2, 1 indicates the chip body, and
It has the same external dimension ratio as the figure.

By the way, the standard dimensions of the conventional product specified in the EIAJ standard are as shown in Table 2, and only the specific portions of the outline symbols 1 and 3 satisfy all the conditions of the present invention.

However, a relatively large-capacity monolithic ceramic capacitor is required for power supply, and an external dimension product of 4.5 × 3.2 × 1.0 mm or more is generally used. 3 watt output with 460kHz switching frequency In the example of DC-DC converter for electronic exchange, 0.33 to 1μF / 100V product on input side 5.7 × 5.0 × 2.0mm)
However, a 10-18μF / 16V product (10 × 6.3 × 3.0mm) large-capacity multilayer ceramic capacitor is used on the output side.

NEC has improved the problem of mechanical resonance of the monolithic ceramic capacitor itself due to the electrostrictive effect as described above. 5.8 x
We have developed the world's first 1μF / 100V and 10μF / 25V products of 2.9 × 1.45mm size.

〔The invention's effect〕

By the way, NEC's Y5U characteristic for high frequency power supply according to the present invention is 10μ.
The mechanical resonance frequency of the F / 25V product due to the electrostrictive effect is 350kHz,
700kHz, 1.4 to 2.2MHz, switching frequency of normal high frequency power supply 430kHz + 100kHz, 460kHz ± 100kHz, 1MHz ± 10
It is outside the range of 0 kHz. In addition, # in the length dimension is the width dimension,
Furthermore, since the width dimension # is the thickness dimension, the frequency of the primary and secondary resonance points, which is the main problem, becomes heavy (the primary resonance point of length 350 kHz, the secondary resonance point of 700 kHz, and the primary resonance point of the width). It has the advantage of having fewer resonance points than conventional products (such as 700 kHz). The effect of the capacitor according to the present invention is proved by the results of mounting the capacitor in a DC-DC converter and testing it.

[Brief description of drawings]

FIG. 1 is an external view of a chip monolithic ceramic capacitor for a high frequency power source according to an embodiment of the present invention, and FIG. 2 is a perspective view of a resin-clad monolithic ceramic capacitor with a lead electrode for a high frequency power source according to the present invention. 1 ... Chip body, 2 ... External electrode, 3 ... Exterior resin,
4 ... Lead electrode.

Claims (3)

[Claims] 1. The ratio of the length, width and thickness of the external dimensions of the chip body is 0.5 ± 20% and 0.25 ± 20% when the length is 1. And monolithic ceramic capacitors. 2. The monolithic ceramic capacitor according to claim 1, wherein the length is 4.5 mm or more. 3. The multilayer ceramic capacitor according to claim 1, wherein the capacitance of the capacitor is 1 μF or more.