JPH03183110A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To reduce the number of resonance points by specifying the size ratio of a length, a width and a thickness regarding the external size of a chip main body. CONSTITUTION:An inversely proportional relationship exists between individual sizes of a laminated ceramic capacitor chip and the mechanical resonance frequency of this capacitor. Consequently, when the chip size of a laminated ceramic capacitor is devised well, the number of mechanical resonance points of the capacitor can be reduced and the capacitor can have the resonance points outside a range of + or -100kHz of a switching frequency of a power supply. That is to say, regarding the ratio of a length, a width and a thickness of external sizes of a chip main body 1, the length is set to 1; then, the width is set to 0.5 + or -20% and the thickness is set to 0.25 + or -20%. Thereby, the mechanical resonance points of the capacitor do not exist within the range of + or -100kHz of the switching frequency of the power supply. As a result, the power supply does not become unstable, and an obstacle such as a radiation of noise radio waves or the like can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilayer ceramic capacitor, and particularly to a multilayer ceramic capacitor for power supply that is suitable for a high frequency switching power supply.

[Conventional technology]

The switching frequency of switching power supplies is increasing year by year, and the mechanical resonance frequency due to the electrostrictive effect of multilayer ceramic capacitors for power supplies, which has not been a problem in the past, is now attracting attention. In conclusion, when the switching frequency of the power supply and the mechanical resonance frequency of the multilayer ceramic capacitor for power supply are close to or coincide with each other, there is a phenomenon that causes malfunction of the power supply. This is largely due to the external dimensions of the capacitor, and the mechanical resonance frequencies due to the electrostrictive effect of laminated ceramic capacitors of conventionally standard sizes are shown in Table 1.

Table 11 (Electrostrictive effect of source chip multilayer ceramic capacitor) As shown in Table 1, there are primary resonance frequencies corresponding to the length, width, and thickness of the multilayer ceramic capacitor.

Furthermore, second-order and third-order resonance points at integral multiples of each frequency are observed. For example, in the case of sample No. 2, 330kHz
z, 430kHz, 660kHz, 860kHz, etc., and especially up to the secondary resonance point becomes a problem.If the switching frequency of the power supply is, for example, 460kHz, if there is a mechanical resonance point of the capacitor within the range of ±100kHz around it, The power supply tends to become unstable, and problems such as noise radio wave emission are likely to occur. Especially for power supply input side filter applications,
This also becomes a problem with multilayer ceramic capacitors used for smoothing the output side.

[Problem to be solved by the invention]

In the example of the sample in Table 1, No. 1 and No. 2 are 460 kHz ± 100 kHz (360 kHz to 5
This becomes a problem because the mechanical resonance point of the capacitor exists within the range (60 kHz).

The problem to be solved is the switching frequency of the power supply ±100
The objective is to ensure that there are no mechanical resonance points of the capacitor within the kHz range and to minimize the number of such resonance points.

[Means for Solving the Problem] It can be seen from the measured values in Table 1 that there is an inversely proportional relationship between each dimension of a multilayer ceramic capacitor chip and the mechanical resonance frequency of this capacitor. is 2
If it is doubled, the resonant frequency will be # times. Therefore, it has been found that by skillfully adjusting the chip size of a multilayer ceramic capacitor, it is possible to reduce the number of mechanical resonance points of the capacitor and to have a resonance point outside the range of the power supply switching frequency of ±100 kHz.

In other words, the external dimensions of the chip body are length and width.

The thickness ratio is 0.5±20 when the length is 1.
% and a thickness of 0.25±20%, and an exterior-type multilayer ceramic capacitor using this chip.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is an external view of a chip multilayer ceramic capacitor for high frequency power supply according to an embodiment of the present invention. FIG. 2 is a perspective view of a resin-clad multilayer ceramic capacitor with lead electrodes for high frequency power supply according to an embodiment of the present invention. In Fig. 1, l is the chip body, 2 is the external electrode, and each dimension of the chip body length #'Ni# thickness is 1 vs. #±20% vs. $±2
The ratio is 0%. In FIG. 2 as well, l indicates the chip body, which has the same external dimension ratio as in FIG. 1.

By the way, the standard dimensions of conventional products stipulated in the EIAJ standard are shown in Table 2, and those that meet all the conditions of the present invention have standard external dimensions only for the specific parts marked with external dimensions 1 and 3.However, for power supplies, the standard dimensions are relatively large. A multilayer ceramic capacitor with a capacity of 4.5 x 3.2 x 1.0 is required for boat fishing.
Products with external dimensions of mm or more are used.

In the example of a 3 watt output electronic exchange DC-DC converter with a 460 kHz switching frequency, the input side tco,
33~1) tF/100V product 5.7 x 5. OX2
, Omm) is on the output side Et! 10-18. ijF'/
A 16V (10x6.3x3.Oam) large-capacity multilayer ceramic capacitor is used.

NEC has improved the mechanical resonance problem of the multilayer ceramic capacitor itself due to the electrostrictive effect as described above. 5.8
We developed the world's first 1pF/100V and 10μF/25V products with a size of X2.9X1.45mm.

〔Effect of the invention〕

By the way, the mechanical resonance frequencies due to the electrostrictive effect of NEC's Y5U characteristic 10μF/25V product for high frequency power supply according to the present invention are 350kHz and 70.0kHz.

It is in the range of 1.4 to 2.2MHz, and the switching frequency of a normal high frequency power supply is 430kHz±100kHz.

460kHz±100kHz, IMHz±100kHz
is outside the range of Moreover, # of the length dimension is the width dimension, and furthermore, # of the width dimension is the thickness dimension, so the frequencies of the primary and secondary resonance points, which are the main problem, become heavier (the primary resonance point of the length is 350kHz, Secondary resonance point 700kHz, I
The primary resonance point of I is 700kHz.

) has the advantage of having fewer resonance points than conventional products. The capacitor according to the present invention was mounted on a DC-DC converter, and the results of tests also demonstrated its effectiveness.

[Brief explanation of drawings]

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

Claims (3)

[Claims] (1) When the length, width, and thickness of the external dimensions of the chip body are 1, the width is 0.5 ± 20% and the thickness is 0.25 ± 20%. A multilayer ceramic capacitor featuring (2) The multilayer 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 capacitor has a capacitance of 1 μF or more.