Classification standard and selection principle of plane transformer

The classification standard of plane transformer and plane transformer generally fall into three categories: PCB type transformer, film type transformer and thick film transformer.

1. PCB type transformer and printed circuit PCB type transformer can save the winding skeleton, increase the heat dissipation area, reduce the eddy current loss caused by skin effect and proximity effect when working at high frequency, and also increase the current density. Its current density can be as high as 20A/mm, with large power and simple process. However, with PCB, the window utilization rate is low, only 0.25~0.3. The window utilization rate of traditional transformer is 0.4, and its volume is also large. The power of PCB type transformer can be up to 20kW, and the frequency can reach the order of megahertz. Pulse plane technology is adopted. Multilayer PCB is sandwiched between magnetic cores. The thin and efficient ferrite plane transformer has a small bottom area, a height of only 7.4mm, a working frequency of 150~750kHz, and a working temperature of - 400~1300.

2. Thin film transformer, thin film transformer is a kind of laminated miniature transformer made of magnetic thin film. The height of the thin film is less than 1mm, and the working frequency is more than 1MHz. It is small and easy to integrate, but only suitable for small power. Most of them are made of metal magnetic materials, such as permalloy, FeSiAl and amorphous alloy. The main reason is that they have high BS and high permeability. Tsuijimotol et al. used belt type (copper thickness 35 μ m. 34mm long and 3mm wide) with insulating film (100 thick μ m) , amorphous CoNbZr film (1.8 μ m) A thin film transformer with controllable output voltage at high frequency, pinhole type transformer, is formed, and the thickness is 210 μ M chip transformer. It adopts two-layer 10 μ It is made of m thick CoZr amorphous film and used for 5V, 0.3A and 1MHz switching power supply. 77.5% ferrite material (mainly MnZn system) can also be made into thin-film transformer. However, it is difficult to produce suitable micro-magnetic film by conventional methods, so it is necessary to develop new film-forming technology. At present, PVD, CVD and other deposition technologies are mainly used in foreign countries, such as chemical etching, laser ablation, light irradiation and low temperature coating. The miniature transformer designed and manufactured by Yamaguchi K and others has an area of only 2.4mm × 3.1 mm, the efficiency can reach 67% at 10 MHz.

3. Thick film transformer is proposed to overcome the defect of large conductor resistance in thin film transformer. The primary and secondary windings are printed on the upper and lower surfaces of the aluminum oxide substrate using the thick film process. The efficiency of the plane transformer made of ferrite is 85% at 2MHz and the output power is 75W. The efficiency of plane transformer manufactured by thick film technology is generally low, so it is the key to realize the high frequency integration of plane transformer to seek further technology to improve the thick film technology of plane transformer manufacturing.

Selection principle of plane transformer

1. Select the corresponding power transformer plane transformer according to the output voltage

2. Determine the number of parallel plane transformers according to the output current

3. The transformation ratio and the number of turns of the primary coil are determined according to the power transformer size of the input and output voltage.

For example, the output voltage of the switch is 5V and the output current is 150A. 5V series plane transformer FTI-12 X 2A-XX is selected. If FTI-12 X 2A-1A is used, five parallel switches are required; If FTI-12 X 2A-5A is used (it is actually composed of five FTI-12 X 2A-1A in parallel), only one is needed.

In addition, it is also necessary to know the change of plane transformer and the number of turns of primary coil in practical application. The transformation ratio can be calculated by the following formula:

Transformation ratio=K X N X P: 1

Where K is the coefficient. When the output of plane transformer is through the center tap, K=0.5; When the plane transformer has no central tap, K=1. N is the number of planar transformer units in parallel. The number of turns on the original side of the P-plane transformer.

In the above example, if the output plane transformer uses the center tap, the input DC voltage is 150V, and the transformation ratio can be set as 10:1, then the original side turns P=10/(0.5X5)=4. If the input DC voltage is 300V and the transformation ratio can be set to 201, then the original side turns P=20/0.5X5=8. It can be seen that the number of turns of the primary winding of the plane transformer is usually small. Basic principles of selection