2, circuit The transformer T1 and transformer isolation from the role of the output inductor to add a Lo ( continued flow of inductance) from the role of energy storage and transmission , the need for reset transformer primary winding Nr ( this point I doubt some reference books Of course there is the best , to take into account the practical application of transformer pin problem) . In actual use , I also found this winding also used RCD snubber circuit Qudai may , if the chip 's power supply with a Fan excited Gong Ji Fu Zhu Ze also be slashed by Tiaozheng Guan 's Bufen peak voltage ( rather a Bufen reset Raozu ) . Output circuit the need for a rectifier diode D1 and a freewheeling diode D2. Because of its use of non- air-gap of the magnetic core transformer , so the copper loss smaller , lower temperature rise transformers . And its smaller output ripple voltage . 3, transformer calculations Generally speaking, the design of high-frequency transformer can be divided into the following six steps: a, selected core materials and core structure . b, determine the operating frequency , the maximum working magnetic flux density Bm. c, calculated and primary core models . d, calculate and adjust of both sides of the turns . e, calculate and determine the wire diameter . f, check the window size and the maximum magnetic flux density Bm. Six steps are discussed in this single -ended forward transformer design: ? selected core materials and core structure High-frequency transformers magnetic selection criteria for the high initial permeability µi, low coercivity Hc, high saturation magnetic induction Bs, low remanence Br, high resistivity ? and the Curie temperature point . High permeability , transformer exciting current work on small ; low coercivity of the hysteresis loss is relatively small ; high saturation magnetic induction , low residual magnetism , transformers work flux range Core structure, the first option to consider forms of energy transfer , and second, consider the geometry constraints, three are considered core cross-sectional area and the ratio of window area , multi-output transformer generally requires a larger window size , select the EE type, EI -type or PQ -type core , can have large windows and good heat dissipation , DC / DC module power supplies can be used FEY -based , FEE -type , EUI -type , etc. , bell transformer required relatively large core cross-sectional area can be used GU -shaped magnetic core ; also should consider the installation of transformers , processing convenience, cost , currently in power is usually used GU -shaped core , this core is characterized by greater cross-sectional area , magnetic flux leakage is small, Using domestic materials , low cost, but need to hand solder outlet . ? determine the frequency , the maximum magnetic flux density Bm Consider the high temperature saturation magnetic flux density Bs to fall , while working to reduce high-frequency core losses , the greatest work of magnetic induction in the general options for the 2000 ~ 2500Gs, the choice of operating frequency transformer can be designed to conduct anti- push , or to determine further Adjustment , AC / DC operating frequency usually choose between 60KHz ~ 150KHz ; DC / DC operating frequency selectable between the 100KHz ~ 400KHz . ? calculated and primary core model Determined based on the core structure , the model chosen area product method can be used : For forward -type transformer : Np = (Vin × Ton) / (?B × Ae) DB can be large , the corresponding reduced transformer size ; high resistivity , high frequency eddy current loss when the work is relatively small; curie temperature point , transformer temperature can be higher , but the above requirements can be met at the same time , different There are bound to magnetic shortcomings of its strengths , needs to be chosen depending on the specific application conditions . A power frequency usually choose between 60KHz ~ 150KHz , secondary power supply products generally chosen frequency between 100KHz ~ 400KHz , in this frequency range , better to use the Mn-Zn ferrite materials, now commonly used iron secondary power supply Oxide materials , including TDK 's PC30-PC40, Magnetics of the P material , PHILIP of 3F3 and 899 plants R2KB2 so . (Ae: core cross-sectional area , Vin: input voltage , Ton: conduction timeDB = Bm-Br, Np number of turns for the transformer primary side ) .h, on- time Ton and the magnetic induction range of workDB, Ae and Q parameters can be obtained product , as the primary basis for core models , if core can choose more experienced over the steps and go directly to the next step . Q = (I1 × Np) / (Ku × j × 2) (Q for the window area , I1, Np corresponding to the primary winding current and turns , Ku is the window coefficient , that is, cross-sectional area of copper and with the window area ratios . General Q preferable 0.3 ~ 0.35, j desirable for the wire current density of 8 ~ 15A / M2, on the assumption that the primary winding type in the total winding cross-sectional area of 1 / 2) Ae × Q = Po / (2 ×h× Ku × j × ?B) According to the output power P0Forecast efficiency ? former vice side calculation and adjust the number of turns a, calculate the primary turns : Np = (Vin × Ton) / (?B × Ae) b, vice side calculation turns : N2 = (Vo + Vd + Io × R) / (D × Vin) (V0The output voltage , VDThe output rectifier diode voltage drop , Io × R for the line voltage drop , Vin for the DC input voltage , D is duty cycle ) c, secondary side current RMS : I2 = Io × sqr (D) d, the primary current rms : I1 = (I2 × N2/Np) × (1 +5%) ( taken as the primary excitation current of the current 5%) According to current experience of RMS and wire selection , taking into account the high frequency skin effect when the wire , when the current is large , multi- unit and around , not more than 2 times per diameter penetration depth , enameled wire of diameter And the number of shares may be adjusted so that each layer line can be just around the bag is full, if the calculated of both sides of turns Fei integer , the party can choose to take the whole Zashu smaller then calculated according to turn other than the winding turns Number . ? Check window and the maximum magnetic induction According to the formula Ku = Ae / Q calibration window, the window coefficient Ku is about 0.3 ~ 0.35 . If the Vice- edge rounding in the calculation of the process of adjusting the number of turns , by the formula Np = (Vin × Ton) / (?B × Ae) Check the maximum magnetic induction , the maximum magnetic induction within the 3000Gs , if qualified , the best test around a Transformer, experiment , and then set the minimum and maximum input voltage waveform when the switch to anti- push ( this method the most effective , of course, the most dangerous , after all, you are not completely out of debugging may blow machine Oh ! best There may be a memory oscilloscope and a colleague in the next ! What do you think ? Oh ~ ~ of course, in real time to the hospital to you friends ! ! ) . 4 , the output inductor design Output filter inductor design is to meet the basic requirements of inductance to ensure maximum current flow through when the core is not saturated , the next window to get around . Single- ended forward circuit design of the output inductor can be divided into the following steps . a, determine the inductance and the primary core models . b, determine the inductor peak current. c, determine the number of coil turns and the air gap . d, determine the wire diameter . e, checking windows and the maximum magnetic induction . ? determine the primary inductance and core models First Circuit determined by the output filter inductance , filter inductance can be reduced to take large number of primary and secondary current peak , reducing the output ripple and noise, but the increase of inductance by the inductor size , size limits , while inductance over the General Assembly Large time constant causes the system to control problematic , current rising slope is too small , use of current control programs Shihai prone to harmonic oscillation , therefore the selection of inductor value should be taken into account the above factors . The selected inductance value, according to the maximum energy storage inductor value 0.5 × L × I × I, based on experience or core manufacturers to provide the Handbook for the chart , a core model on behalf of the primary steps into the future calculation . ? determine the inductor peak current Imax = Io +2 × Vo × Toff / L (Toff for the off-time ) ? determine the number of turns and air gap Because there is a big inductor current in the DC component , was elected with a ferrite core , be sure to join the air gap , the actual commissioning in the size of the adjustment of air gap ; also consider using PPM FeSiAl material or magnetic material ( Oh ~ ~ I can not think a bad idea Oh ! effect would a lot better , but some will power more valuable Bale !!!)? General output filter inductor can be chosen as the maximum magnetic flux density around 3000Gs , after the United Solution Bm selected type can be obtained for more than two turns N and the gap lengthd. Turns N should be rounded , less current great time when the number of turns , half turns should be taken to avoid the situation . ? calculate and determine the wire diameter After determining the number of turns , wire diameter selected according to the current RMS current is large , multi- unit and still around , but because of the inductor current in the AC component is small, the skin effect is not obvious , if necessary, use coarse Wire winding . ? Check window and the maximum magnetic induction Inductance design is completed , may further adjust the air gap in the experiment in order to achieve the best work of inductance and magnetic flux .