《平面变压器设计(design of planar transformer)0》.pdfVIP

Desgin of planar transformer Contents: Induction Design procedure Design examples –flyback Formuals Layer desgin Introduction Planar transformes can be constructed as stand alone components ,with a stacked layer desgin or a small multilayer PCB,or integrated into amultilater board of the power supply. Important advantages of planar magnetics are: very low profile excellent thermal characteristics low leakage inductance excellent repeatability of properties Design procedure 1) Calculation of maximum flux density: The core and copper loss in a transformer under operating Conditions will induce a temperature rise ! 2) In thermal equilibrium the total losses in the transformer(Ptrafo). Can be related to a temperature rise △T of the transformer with an analogous of Ohm’s law by : Ptrafo=△T / Rth Notes: in this formula Rth represents the thermal resistance of the Transformer . Ptrafo: can in fact interpreted as the cooling capability of the transformer. Design procedure(addPc) With the assumption that half of the total transformer loss is core Loss , it is possible to express the maximum core loss density Pc As a function of the allowed temperature rise △T of the transformer as ; Pc = 12* △T / √Ve (mW /cm*3) Previous work ,showed that it is possible to establish an empirical formula which relates the value of thermal resistance of a transformer directly to the value of the effective magnetic volume Ve of the ferrite core used . Design procedure(addPcore) Power losses in our ferrites have been measured as a function of frequency(f in HZ), peak flux density (B in T) and temperature (T in℃). Core loss density can be approximated by the following formula : In this formula Cm, x,y,ct0,ct1 and ct2 are parameters which have been found by curve fitting of the measured power loss data .they are dimensioned in such a way tha