Design of 30kHz High Frequency Switching Power Supply Transformer

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Design of 30kHz High Frequency Switching Power Supply Transformer [Copy link]

In the traditional high-frequency transformer design, due to the limitation of the core material, its operating frequency is relatively low, generally around 20kHz. With the continuous development of power supply technology, the miniaturization, high frequency and high power ratio of power supply system have become an eternal research direction and development trend. Therefore, the research on power transformers with higher frequency is the key factor to reduce the volume of power supply system and improve the power output ratio of power supply. Based on the excellent electromagnetic properties of ultra-fine crystal alloy, this paper introduces the design of 30kHz ultra-fine crystal high frequency switching power supply transformer by example.

1 Transformer performance indicators
Operating frequency f: 30kHz

　　Converter input voltage Ui: DC300V

　　Converter output voltage U0: DC2100V

　　Converter output current Io: 0.08A

　　Rectification circuit: bridge rectifier

　　Duty cycle D: 1%～90%

　　Output efficiency η: ≥80％

　　Withstand voltage: DC12kV

　　Temperature rise: +50℃

　　Working environment conditions: -55℃～+85℃

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2 Selection of transformer core and determination of working point From the performance index requirements of the transformer, it can be seen that traditional thin-strip silicon steel and ferrite materials are difficult to meet the design requirements of the transformer in terms of frequency and use environment. The materials of the core can only be considered from three materials: Permalloy, cobalt-based amorphous alloy and ultra-fine crystal alloy. However, the price of Permalloy and cobalt-based amorphous alloy is high, which is about several times that of ultra-fine crystal alloy, while the saturation magnetic induction intensity Bs is about 2/3 of that of ultra-fine crystal alloy, and the processing technology is complicated. Therefore, based on the comprehensive performance comparison of the three materials (Table 1), the selection of ultra-fine crystal alloy with high saturation magnetic induction intensity Bs, good temperature stability, low price and convenient processing is conducive to the realization of transformer technical indicators. Figure 1 (1) Comparison of the main magnetic properties of cobalt-based amorphous alloys and ultrafine-grained alloys Material Saturation magnetic induction intensity/T Coercive force/A·m－1 Curie temperature/℃ Specific loss 20kHz0.5T/W·kg－1 Operating frequency/kHz Operating temperature/℃ Ultrafine-grained alloy 1.2 0.48～1.2 25 ～150 ～150 Cobalt-based amorphous 0.8 1.2 340 20 ～100 ～120 Permalloy 0.7 1.99 480 30 ～50 ～200 The selection of the core operating point is often based on factors such as the core material, the operating state of the transformer, the operating frequency, the output power, and the insulation withstand voltage. The saturation magnetic flux density Bs of the ultra-fine crystal alloy is as high as about 1.2T. In the design of the bipolar switching power supply transformer, the maximum working magnetic flux density Bm of the magnetic core can generally be taken to 0.6~0.7T. After special treatment of the magnetic core, Bm can reach 0.9T. In this design, due to the operating frequency, insulation withstand voltage, and use environment, the maximum working magnetic flux density Bm is set at 0.6T, and the magnetic core structure is set as a rectangular magnetic core without cuts. Compared with the annular magnetic core, this structure of the magnetic core has the advantages of convenient coil winding, small influence of distributed parameters, high utilization rate of the magnetic core window, good heat dissipation, reliable system insulation, but poor electromagnetic compatibility.

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3 Calculation of the main parameters of the transformer 3.1 Calculation of the power of the transformer When the output circuit of the half-bridge converter is a bridge rectifier, the calculated power of its switching power transformer is: Pt=UoIo(1+1/η)(1) Substituting Uo=2100V, Io=0.08A, η=80% into formula (1), we can get Pt=378W. 3.2 Design output capacity of the transformer The design output capacity of the transformer is: Ap=(Pt·104/4BmfKWKJ)1.16（2） Where: the operating frequency f is 30kHz, the working magnetic induction intensity Bm is 0.6T, the window space factor KW of the magnetic core is 0.2, and the current density KJ of the rectangular magnetic core (when the temperature rise is 50℃) is 468. After calculation, the design output capacity of the transformer AP=0.511cm4. 3.3 Actual output capacity of transformer Iron-based ultra-fine crystal core and ultra-fine crystal soft magnetic alloy passed provincial technical appraisal On October 24, 1999, the new product DY-ON iron-based ultra-fine crystal core and ultra-fine crystal soft magnetic alloy developed by Jiangxi Dayou Technology Co., Ltd., entrusted by Jiangxi Provincial Science and Technology Commission and other agencies, passed the provincial technical appraisal and received high praise from experts and scholars at the meeting. They all agreed that the two products have stable performance and various technical indicators meet the technical requirements of the US UL94-P standard and the national standard GBm292-89, respectively, and are unique among similar domestic products. Amorphous (ultra-fine crystal) soft magnetic alloy is one of the six new high-tech materials in the world in the 1990s. It has excellent characteristics and is currently in short supply in the domestic market, with broad prospects. Contact: Fang Huaping, Yichun Regional Grain Bureau, No. 62, Dongfeng Street, Yichun City, Jiangxi Province (336000) The output capacity of the transformer is the output capacity of the core, which depends on the product of the core area (AP), which is equal to the product of the effective cross-sectional area (AC) of the core and its window cross-sectional area (Am), that is: AP = ACAm (3) In the design of the transformer, the output capacity of the transformer must be greater than its design output capacity. In the design, the size of the rectangular core we selected is: 10×10×39×13.4 (that is: a=10mm, b=10mm, c=13.4mm, h=39mm), the actual AP reaches 3.66cm4 (where the space factor KC of the core cross-sectional area is 0.7), which is greater than the design output capacity of the transformer 0.511cm4, so the core can meet the design requirements. 3.4 Calculation of primary turns of winding: D is taken as 50%, Ton=D/f=0.5/(30×103)=16.67μs, ignore the voltage drop of the switch tube, Up1=Ui/2=150V. N1=Up1Ton10－2/2BmAc=(150×16.67)10－2 /(2×0.6×1×1×0.7)=29.77 turns. Take N1=30 turns. Secondary turns: Ignore the voltage drop of the rectifier tube, Up2=Uo=2100V. N2=Up2N1/Up1=(30×2100)/150=420 turns 3.5 Conductor wire diameter Ip1=Up2Ip2/Up1=0.08×2100/150=1.12A Current density: J=KjAp－0.1410－2=468×0.511－0.14 ×10－2=5.14A/mm2 Considering the wire loss and temperature rise, the current density is set to 4A/mm2 (1) Primary winding: The cross-sectional area of the wire is calculated to be Sm1=Ip1/J=1.12/4=0.28mm2 The wire diameter of the primary winding can be selected as d=0.63mm, and its cross-sectional area is 0.312mm2 of round copper wire. (2) Secondary winding: The cross-sectional area of the wire is calculated to be Sm2=Ip2/J=0.08/4=0.02mm2. The wire diameter of the secondary winding can be selected as round copper wire with a diameter of d=0.16mm, and its cross-sectional area is 0.02mm2. In order to facilitate coil winding, a thicker wire can also be selected.

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4 Coil Winding and Insulation To reduce the influence of distributed parameters, the primary adopts a double-leg parallel winding structure, and the secondary adopts segmented winding and series connection to reduce the voltage difference between windings and improve the reliability of the transformer. The thickness of the coil after winding is about 4.5mm. It is less than half of the core window width of 13.4mm. In terms of transformer insulation, the coil insulation uses composite fiber insulation paper with high electrical strength and low dielectric loss to improve the insulation strength and corona resistance between the primary and secondary. The transformer insulation adopts the overall infusion method to ensure the insulation requirements of the transformer.

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The ultra-microcrystalline switching power supply transformer has passed the product electrical performance test and airborne environmental test after epoxy infusion insulation, and has been used in airborne equipment. The temperature rise of the transformer is <35℃, the working efficiency is more than 90%, and the waveform quality is excellent, and the electrical performance parameters are stable. Ultra-microcrystalline alloy strip is a new type of soft magnetic alloy with excellent electromagnetic properties, low price, strong environmental adaptability, and has broad application prospects in the field of high-frequency electromagnetic components, especially in power supplies, excitation transformers, inductors, etc. in array radar systems. Under the use conditions of 100kHz, it can replace ferrite and Permalloy as a core material.

wufengdj

The coil is being wound! ! Thanks for the information! !

fdq236

Hey, why is my coil not working? Please help me.

280237474

Thank you, this is great stuff. We need to study this.

quanzx

I appreciate your advice. The host said it well. Thank you

zhuozhongchang

Good stuff, thank you sir

zhaokbk

Thank you

p.s. I have compiled the post by lz in the doc below. . ;P

zchen6127

Thanks