Technologies for Developing and Designing CRT Ferrite Core Materials

The demand for optimal design technologies for cathode-ray tube (CRT) components is increasing, thus enabling TVs and other image-display equipment to have larger and wider screens, higher image quality, and lower power consumption. To achieve these goals, it is important to use low-loss ferrite components in deflection circuits, high-voltage circuits and other CRT sections, because low-loss ferrites reduce heat generation and thus ensure greater safety. We, therefore, report on the latest technologies applied to the development of low-loss ferrites, and introduce recent design technologies based on computer-simulated design of ferrite core materials and computer-simulated analyses of magnetic fields and heat generation.
 1. INTRODUCTION
Television is one of the most popular inventions of the 20th century. Recently, however, there has been a growing need for new CRTs with brighter, higher definition, flatter and larger screens, as is evident in the commercialization of liquid crystal displays. In response, ferrite components for CRTs will have to become smaller and lighter while achieving higher performance levels. At the same time, Japanese ferrite component makers are being compelled to reduce production costs to overcome the yen's rising exchange rate. Accordingly, it is now imperative that CRT ferrite components incorporate both performance and cost advantages, starting with the design stage. Figure 1 shows a circuit diagram of a TV receiver with a built-in satellite broadcast tuner. TVs and other image displays incorporate a variety of ferrite components, such as deflection yokes, flyback transformers (FBT), convergence components, linearity coils, transformer choke coils and noise suppression devices. These components use Mn-Zn, Mg-Zn or Ni- Zn ferrites. In this report, we shall examine the ferrites used for deflection yokes and flyback transformers.
2.FERRITE MATERIALS AND APPLICATIONS
 Figure 2 summarizes the major ferrite technologies that have been developed since the start of TV broadcasting.  
2-1.Materials for Deflection Yoke Ferrites
  From 1955 to 1965, when ferrites were first applied to electron beam deflection, Mn-Zn or Ni-Zn ferrites were used. Providing lower resistance, Mn-Zn ferrites were used with saddle toroidal winding. But due to ringing problems, they were gradually replaced by Ni-Zn ferrites, which featured higher resistance. Currently, Japanese makers mainly select Mg-Zn ferrites for their low material costs. Tables 1 and 2 compare the characteristics of different ferrite core materials. Table 3 lists the ferrite core requirements as seen from the producers of deflection yokes. In displays with a 120 kHz horizontal scanning frequency, Mn- Zn ferrites may be employed and, in some special cases, slot- type core shapes are adopted to allow different winding patterns for better heat dissipation.
Table-1 Comparison Table of Ferrite Material for DY Use

Property Mg-Zn Ni-Zn Mn-Zn
Core for Deflection Yoke Core Loss
Saturated Magnetic Flux Density
Resistivity
AC Initial Permeability
Curie Temperature
Deflection Yoke Coil Rise in Temperature
Ringing
Cross Talk
Beats
Cost
Total Cost Performance

Table-2 Standard Material Characteristics of Ferrite Cores for Deflection Yokes
Property Symbol Unit Condition DY-1
Mg-Zn 		DY-2
Mg-Zn 		DY-3
Mn-Zn 		DY-4
Ni-Zn
AC Initial Permeability - 0.1 MHz 350 380 1800 500
Saturation Magnetic Flux Density Bs mT 23C 230 250 500 360
100C 160 170 400 295
Corecivity Hc A/m 23C 50 30 20 36
Relative Loss Factor 0.1 MHz < 50 <120 < 5 < 30
Core Loss Pc kW/m3 25 kHz
(100 mT) 		23C 420 230 90 280
60C 380 170 70 280
100C 430 170 60 260
100 kHz
(100 mT) 		23C 1500 1000 270 960
60 C 1470 850 230 950
100 C 1640 860 180 940
Curie Temperature Tc C - >145 >145 >180 >200
Resistivity - 105 105 1 105

Table-3 Customer Needs for Deflection Yoke Cores
Field Use Customer's Request
Consumer
TV 		Deflection Angel 110 Low Cost
Monitor Horizontal Scanning
Frequency 90 KHz

Precision(Inner Dimension,Roundness)High Saturated Magnetic Flux Density Low Core Loss
High Frequency Monitor Horizontal Scanning frequency 90-130 kHz

Precision(Dimension)High Saturated Magnetic Flux Density Low Core Loss
HDTV

Deflection Angel 110
Double Scan

Low Cost Precision(Dimension,Roundness) High Saturated Magnetic Flux Density Low Core Loss

2-2.Materials for Flyback Transformers
Mn-Zn ferrites have the advantage of low loss and high saturation flux density, making them suitable core materials for transformers. Furthermore, their core loss performance is being improved, using micro-crystal structure control technologies. Table 4 shows the characteristics of FBT ferrites in practical use over recent years. Since heat generation inside FBTs must be minimized to ensure safety, utmost efforts have been exerted to reduce core loss. In addition, efforts have been made to curb the core base diameter so as to reduce core material costs, core size and weight. Figure 5 presents the history of core loss reduction through the development of new production processes and new element technologies. Today, the average core loss is only one-fifth or one-sixth of the initial levels, when ferrite cores were first applied to FBTs.
Table-4 Standard material characteristics of ferrite cores for flyback transformers
Property Symbol Unit Condition FBT-1 FBT-2 FBT-3
AC Initial Permeability - 100 KHz 1800 2300 2200
Saturation Magnetic Flux Density Bs mT 23C 520 500 500
100C 420 400 400
Corecivity Hc A/m 23C 13 13 13
Relative Loss Factor 0.1 MHz < 5 < 5 < 5
Core Loss Pc kW/m3 16 kHz
(150 mT) 		60C 5.4 4.6 3.8
80C 3.9 3.5 2.9
100C 3.5 3.3 2.7
32 kHz
(200 mT) 		60 C 24 22 18
80 C 19 18 15
100 C 17 16 13
50 kHz
(200 mT) 		60 C 43 39 32
80 C 36 33 27
100 C 32 29 24
100 kHz
(200 mT) 		60 C 110 100 82
80 C 95 88 72
100 C 90 85 70
Curie Temperature Tc C - >200 >200 >200
Temperature Coefficient in Permeability X10-6 20 - 80C 8 6 6
Resistivity - 3 3 3
3.HIGH-PRECISION PROCESSING TECHNOLOGIES
3-1.Precise Dimensions of Deflection Yoke Cores
In the design of deflection yokes, the saddle-saddle winding method has been adopted in answer to the growing need for higher quality image displays. Since this requires greater convergence precision, it is increasingly important to achieve higher precision in core dimensions. Dimensional precision has been improved mainly by NC processing machines, which can grind the curved surfaces of cores with higher precision, so that the gaps between the coil and core are drastically reduced for higher convergence precision.
3-2.Gap Surface Grinding for FBT Cores

In recent years, core design has seen a rapid change, that is from split winding to layer winding in order to prevent rare shorting in high-voltage areas and to realize uniform winding density. While layer winding partially solves ringing problems, efforts are also being made to enhance gap surface grinding precision and to minimize sintering deformation for the correction of ringing. Furthermore, higher precision in grinding and sintering is in greater demand due to the ongoing changes in core coupling methods, from the use of metallic clamps to the use of glues. Because high-voltage FBT cores require wider gaps between the core and coil, the tolerance for inductance must be below +2.5%. Thus, gap grinding precision must be improved to a level that is no more than 10 um deviation in the case of high-voltage FBT cores.

4.DESIGN OF FERRITE COMPONENTS USING A CAE SYSTEM
In order to put an end to the inefficient development of new ferrite components based on trial and error, we have been utilizing the computer-aided engineering (CAE) technique as a design tool for magnetic components since 1984. We now have a ferrite material design system (MAGSYS-F) and a magnetic field analysis system (S-FIAS). As a result, it has become possible to simulate heat generation in planned ferrite components, thus remarkably cutting the design time and improving the design accuracy.
4-1.Ferrite Material Design System (MAGSYS-F)
MAGSYS-F is used to predetermine manufacturing conditions that will meet the customer's specification requirements. It adopts artificial intelligence technologies to enable the systematic utilization of theoretical, experimental and empirical data bases. By indicating the experimental conditions, the design engineer can obtain from MAGSYS-F suitable manufacturing conditions in the form of graphs and tables. For example, Figure 6 compares the actual measurement values and MAGSYS-F output values concerning the ferrite loss coefficient and disaccommodation of a Mn-Zn ferrite.
4-2.General-purpose Magnetic Field Analysis System (S-FIAS)

We have developed a software program to simulate the electromagnetic characteristics of axial-symmetry coils, applying the marginal element method. By inputting customer specifications on core shape, materials, winding shape, input signals and ambient conditions, we can obtain from S-FIAS the data needed to design a coil. Through repeated simulations using varied input data, it is possible to determine the optimal design specifications for a coil product. Figure 7 provides a flow chart of simulation steps, from data input to output. Table 5 lists the output data items available from S-FIAS, for the design of coil products. These items include inductance, mutual inductance, leakage flux, DC overlap characteristics, and flux distribution.

Table-5 Application & Output Items.
Application CAE System FDK core name Output Items
Inductance Mutual Inductance Leackage Flux DC Bias Flux Density Distribusion Core Heat Evolution
Deflection Yoke SUPER-
FIAS 		DY DP - - -
Flyback Transformaer SUPER-
FIAS 		RU RUI
Switching Power Supply Transformer SUPER-
FIAS 		EI
EP
EED
PM
EE
EER
RM X
UU
UI
Small Core for Radio FIAS B FR TP
TF
LP 		- -
Common Mode Choke Coil SUPER-
FIAS 		FR
EE
EI

4-3.Heat Generation Analysis System

Thanks to the development of the ferrite material design system and the general-purpose three-dimensional magnetic field analysis system, we are now able to determine the safe designs of various magnetic components, including deflection yokes and FBT ferrite cores. Especially in the case of deflection yokes and FBT ferrite cores, which are TV components, the prevention of excessive heat generation from coils is of crucial importance, since TVs operate with a large amount of electric power. By building up heat dissipation data bases in relation to the ambient conditions, coil conditions, component materials, and circuit layouts and by utilizing a load simulation system for ferrite cores, we have enabled the simulation of heat generation in magnetic components. Figure 8 shows a the simulated flux distribution inside a ferrite core for a 49cm-size display, when electricity of fH = 64 kHz and fV = 64 Hz is applied. Figure 9 shows the simulated heat distribution in that core, with the sizes of the core and coil reduced to one-fourth scale.
5.CONCLUSION

The first ferrites were invented in Japan about 60 years ago. Over the past ten years or so, we have rapidly increased our know-how in selecting the most suitable ferrite materials from a vast selection, a result of improved computer technology. To our delight, computer simulation has realized two-way design communication in which the maker designs ferrite materials in response to customer needs. Our CAE technology is also applied to the design of CRTs for Hi-Vision and other large-screen television receivers. With the CAE technology, new ferrite materials are being developed while constantly referring to customer needs. Our current challenge is to construct data bases intended for the design simulation of host equipment as well as of components. This should bring about an even higher level of simulation accuracy.

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