Research And Design Of Planar Miniaturized Transformer

In the recent years,the switching power supply technology has been developing towards the direction of miniaturization,high integration and high power density.Therefore,it is a challenging task to meet certain index requirements such as loss,leakage inductance,and distributed capacitance under the premise of making the device as small as possible.In switching power supplies,magnetic components such as inductors or transformers occupy a large volume,generally account for more than 35%.In that,the key problem lies in how to keep the loss and parasitic parameters of the magnetic element small even when the volume is small.The technology currently used in miniaturization is planar inductance or planar transformer technology.Compared with traditional wirewound transformers,planar transformers use low-profile magnetic cores and flat windings,so the profile can be very low.Generally,the volume of a planar transformer is only 20%～30% of the volume of traditional wire-wound transformers.The flat magnetic core and windings have a large area contact with the external environment which cause a good heat dissipation and can further reduce the loss of the transformer.In order to realize that the transformer satisfies the requirements of certain performance indicators in the smallest possible volume,this paper conducts the research on planar transformers as follows:First,the various manufacturing technologies of planar transformers are studied,and the advantages and disadvantages of each process and its applicable occasions are pointed out.From all aspects of the process comparison,it is pointed out that the PCB technology has the least impact on the parasitic parameters and losses of the planar transformer in the planar transformer design.Second,the different effects of different arrangements of planar windings on transformer performance are studied.Analyzing and deriving from a theoretical point of view,it is concluded that the reason that affects the winding loss and leakage inductance is the magnitude of the magnetic field strength between the windings,and then three different representative winding arrangements are studied,namely non-cross winding,mode,partial cross winding mode and full cross winding mode.The effects of these three winding arrangements on transformer winding losses and leakage inductance are analyzed,and verified by actual simulations.The theoretical analysis obtained is consistent with the actual simulation results.Third,based on the previous research on different winding arrangements,two singleended flyback planar transformers based on the primary-side feedback topology were designed using a completely cross-winding mode and working at frequencies of 100 KHz and 250 KHz respectively.Starting from the working principle of the flyback circuit,the specific design formula and process of the flyback planar transformer are given.In the case of meeting the design index requirements,the primary and secondary windings are completely cross-arranged,and the auxiliary winding is placed at the top of the magnetic core.This method can not only meet the requirements of the design index,but also reduce the complexity of the design.Fourth,the magnetic circuit method is introduced into the Steinmetz empirical formula to calculate the core loss with an air gap.The core loss of ring core single winding and multi-winding at different frequencies and different excitation amplitudes and the core loss of EE13-6-6 core under different frequencies and different excitation amplitudes are studied respectively.And on the basis of this method,a more accurate calculation method is proposed for the loss calculation of the used EE core.