1 Introduction

Planar cores developed, can realize the transformer design graphic. The planar transformer magnetic core, windings requirements is a planar structure, so it should be adopted multi-layer winding of PCB. Now, many companies havedeveloped a planar transformer, Pulse company developed a planar magnetic components, Israel Payton company Payton has developed a Planetics planar transformer, power from 5W to 20KW, the frequency from 20KHz to 2MHz,efficiency is usually up to 98%, is the ideal choice for telecommunications,electric welding machine, computer and peripherals, network, medical electronics, industrial control, security system and electronic equipment.

The characteristic of planar transformer is high frequency, low profile, high is very small and very high frequency.

Transformer is one of the key elements in a power supply. The traditional transformer is composed of ferrite core and coil of copper wire, size and it is easy to generate electromagnetic interference. Planar transformer (PlanarTransformer) can effectively solve the problem of volume and high frequency.

Compared with the traditional transformer planar transformer is the biggest difference between the core and the coil winding. Planar transformer with E type,small size RM or ring type ferrite core, usually made of high frequency power ferrite material, has lower core loss at high frequency; the winding adoptsmultilayer printed circuit board and wound together, winding or copper laminationinto a magnetic loop transformer in high frequency core plane on the. The design of DC copper resistance, low low leakage inductance and distributed capacitance, which can meet the design requirements of the resonant circuit.And because the magnetic shielding core good, can suppress the RF interference.

2 classification

Classification of planar transformer: different planar transformer according to the design of the production process, can be divided into printed circuit (PCB) type,thick film, thin film type, sub micron type 4.

PCB type transformer

Printed circuit PCB (printedcircuit board) type transformer winding skeleton can be omitted, can increase the heat dissipation area, can reduce the eddy currentloss caused by operating at high frequency by the skin effect and proximity effect, also can increase the current density, the current density of up to20A/mm, high power, simple process. But PCB, the low utilization rate of the window, only 0.25~0.3, the traditional transformer window utilization rate was 0.4,the volume is large. PCB type transformer and its power can be up to 20kWorders of magnitude, frequency up to mhz. The plane of pulse, multilayer PCBclamp between the cores, thin high potential iron ferrite planar transformer, the bottom area is small, height of only 7.4mm, the frequency of 150~750kHz, the working temperature is -400~1300.

Thick film transformer

Thick film transformer was proposed to overcome the defects of thin filmtransformer conductor resistance. The alumina matrix, using thick film technology, in which, under the surface of the printed the primary and secondary windings, planar transformer ferrite produced in 2MHz, the output power is 75W,the efficiency of up to 85%. Planar transformer efficiency of thick film technology to manufacture are generally low, and therefore seek further technology to improve the thick film planar transformer manufacturing technology is the key to realize high frequency integrated planar transformer.

Film type transformer

Film type transformer is the development of a magnetic thin films for laminatedmicro transformer, the film height less than 1mm, the operating frequency is more than 1MHz, which has the advantages of small volume, easy integration, but is only suitable for small power. Most of them using metal magnetic material, such as po Mo alloy, Fe Si Al and amorphous alloy. Mainly because of their high BS and high permeability. The belt by Tsuijimotl et al (Cu thickness of 35 μ m, long 34mm, wide 3mm) to the insulating film (thickness of 100 μ m), amorphous CoNbZr film (1.8 μ m) to form a thin film transformer voltage controllable output at high frequencies -- pinhole type transformer, also made the chip transformer thickness of 210 μ M. It adopts two layers of 10 μ m thick amorphous CoZr thin film made, switching power supply for 5V, 0.3A, 1MHz, 77.5% ferrite material(MnZn based) can also be made into a film type transformer, but with the conventional method is very difficult to produce micro magnetic film suitable, so it needs to be developed into membrane technology is a new. At present mainly uses PVD, CVD deposition technique combined with chemical etching, laser ablation method, membrane technology into light low temperature coating method. Yamaguchi K design of a miniature transformer, its area is 2.4mm *3.1mm, in the 10MHz efficiency of up to

Submicron type transformer

Sub micron transformer is the use of chemical synthesis, using the low temperature (900 ℃) NiCuZn ferrite sintered as medium material, with Ag as the internal electrode, method for casting and screen printing technology preparationand become, its small size, light weight, easy integration, simple process. The twotype of sub micron type transformer, dimensions were 2.1cm × 2.1cm × 1mm and 8mm × 8mm × 1mm, design pressure ratio were 6 and 4, the frequency of 1~10MHz. Sub micron planar transformer has the advantages of novel structure, changed the structure of traditional transformer, the transformer primary side and secondary side winding with screen printing technology firing in ferrite, theappearance is similar to the integrated circuit device attached to the table. Measurements of the electrical properties of sub micron planar transformer shows that: ① no-load condition, voltage ratio first increases with the increase ofthe input voltage, and then decreases with the increase of the input voltage, maximum range. In addition, transformer ratio increases with increasing thefrequency of input signal. In some cases the input voltage and frequency, output power with the load increasing first increased and then decreased, there exists a maximum output power of the load resistance value. In a certain input voltage and output load condition, with the increase of the frequency of the input voltage, transformer voltage ratio increases, when the frequency of the input voltage ishigher than a certain critical value, voltage ratio remained unchanged. Waveform distortion decreases with the frequency of the input voltage. Under a fixed frequency, there is a saturation value of load resistance, when the load resistance value is less than the saturated load resistance value, the output voltage is increased with the increase of load of the transformer, but when the load resistance is greater than the value of saturated load resistance value, theoutput voltage changes very little or almost unchanged. With the increase of frequency of saturated load resistance gradually increases. In the load resistance value is equal to the saturation value of load resistance, transformer transformer changes than do not vary with the input voltage changes, but with the increase of the input voltage, input voltage and the output voltage waveform distortion degree enhancement.

Compared with the traditional transformer 3 has the following main features:

(1) high current density. Wire planar transformer is actually the conductor plane,so the current density.

(2) high efficiency. Efficiency can reach 98% ~ 99%.

(3) low leakage inductance. The 0.2% is about the primary inductance.

(4) a good heat conduction. Hot channel of short distance, low temperature rise.

(5) low EMI radiation. Magnetic shielding good radiation can be reduced to very low.

(6) small volume. A small core can be correspondingly reduced volume.

(7) parameter repeatability. Because the winding structure is fixed, pre processed, so the parameter stability.

(8) wide operating frequency range. Frequency is from 50 kHz to 2 MHz.

(9) wide operating temperature range. The working temperature is -40 ℃ ~ 130 ℃.

(10) and good insulation. Planar transformer is composed of conductive circuit and insulating sheet overlap each other, so as to ensure the winding, primarysecondary and secondary - secondary rooms up to 4 kV insulation.

The use of 4 planar transformer in switch power supply

(1) in addition to the rational layout and the control circuit uses surface mount technology to save space, the more effective measures are taken to avoid thehigh frequency power transformer traditional large occupy the limited space.

(2) high temperature working environment. Compared with other rectifier module-25 ℃ ~ +50 ℃ working environment,

The module can work in the environment of -25 ℃ ~ +70 ℃ in some bad conditions, in order to meet the demand. Therefore, when in normal work, will be more high temperature internal module, requirements of the transformer can withstand high temperatures.

(3) the module of EMI, the requirement of high noise. Requirements of practical measures to improve these aspects.

(4) the module has the advantages of small size, high efficiency, small heat loss and indirect request module.

In view of some requirements above, combined with the advantages of planar transformer, the transformer design to give priority to the planar transformer. Inthe structure volume is small, the current density of planar transformer leakage reactance of the high, low, switching power supply is very suitable for low voltage and high current. It should be noted that, due to the conventional transformer arecylindrical wire wound on ferrite core, high frequency current concentration in the vicinity of the conductor surface (skin effect), which will reduce the effectiveconductivity. In the planar transformer, its "winding" is printed flat conducting wireon the circuit board on the copper cladding. The flat geometry reduces the lossof skin effect at higher switching frequency. Therefore, the most effective use ofthe surface conductivity of copper conductors, efficiency than traditional high.

Technical advantage 5 planar transformer in switch power supply

Abstract:

High power density is the main trend of the development of the switching power supply, to do this, we must increase the power density of planar transformermagnetic components because of the close coupled planar structure and windingspecial, so the high frequency parasitic parameters is greatly reduced, greatlyimproved the working state of the switching power supply, so it has been widely used to study several different plane structure and winding making way,introduced a standard design method for planar transformer, which makes the design process more simple, greatly reducing the design cost. Finally, someparameters of planar transformer and traditional transformer are compared, and gives the design principles.

Keywords: planar transformer; leakage; insertion technique

Introduction

The design of the magnetic components is an important part of switch power supply, because the planar transformer has a lot of advantages in improving theproperties of switching power supply, so it has been widely applied in recent years. For an ideal transformer, magnetic flux generated by the primary coilpasses through the secondary coil, i.e. no leakage flux. While the general transformer, magnetic flux is not generated by the primary coil passes throughthe secondary coil, and thus a leakage inductance, close the electromagnetic coupling can not meet the requirements of. The planar transformer only one turnmesh secondary winding, the winding is also different from the traditionalenameled wire, but a piece of copper sheet, stick around the same size stampingferrite core surface. Therefore, the output voltage depends on number of planar transformer cores, and the output current of planar transformer can be expandedby parallel, in order to meet the design requirements. Therefore, the characteristic of planar transformer is obviously: tightly coupled planar windingleakage are greatly reduced; planar transformer special structure makes it verylow, which makes the converter is conceived in a plate to obtain the realization.However, the very high capacitance effect problem of planar structure, greatly limits its large-scale use, however, these shortcomings in certain applications,may also be converted to an advantage. In addition, the plane of the core structure of the radiating area is enlarged, is conducive to the transformer radiator.