PM Shaped Magnetic Core For Switching Power Supply

1 Introduction

It is well known that the geometry of the magnetic core affects the shielding, leakage inductance, winding and installation of the coil. When the core is installed, the coil should be shielded, the leakage inductance is small, and the winding wire is convenient. PM core (Pot Module Cores pot core components) from pot core (Pot), due to accommodate with wire coil skeleton pin of the incision, these pins can be installed in accordance with standard pot core design module (Module) on the printed circuit board, hence the name PM core. IEC1247 (1995, first edition) "PM core and attachment dimensions" made of magnetic oxide provides the basic size of coil skeleton PM core size, and with the core in turn lead pin in printed circuit core network relatively basic contour position, and provides the effective parameters of core value. The standard provisions of the PM50/39, PM62/49, PM74/59, PM87/70, PM114/93 and other five kinds of specifications of the size of the magnetic core and related information.

2 shape features

The outline of the PM shaped magnetic core is shown in Figure 1. It is formed by the pot shaped magnetic core, on the one hand, it has the advantages of the tin core: the magnetic circuit is closed, the magnetic flux leakage is small, the effective area is large, the magnetic core coefficient C1 is small, and the air gap can be controlled. Due to its wide wire slot, it allows the use of thicker copper wire welding, the distance between the lead column is wider, can withstand enough pressure and through the larger current. Therefore, the PM shaped magnetic core can be regarded as an extension of the tank shaped magnetic core for the application of high power applications. On the other hand, because the pot core coil is wrapped outside the core, the outer circumference of the magnetic core provides good shielding in the circuit, can eliminate the adjacent electromagnetic coupling between the components, and can solve the inconvenience of winding, but the drawback is that bad heat, high temperature rise, while the PM core is the tank the outer circle shaped magnetic core part is cut off, the core center column good ventilation, conducive to heat, so as to solve the problem of high temperature rise.

3 magnetic core design features

The PM shaped magnetic core has the advantages of reasonable design, reduced leakage inductance, small temperature rise of the magnetic core and so on:

For switching power supply transformer, the transformer has a certain amount of inductance, such as the primary inductance

Among them: for the magnetic core amplitude permeability

Number of turns of the primary coil

For the magnetic core constant

Because the switching power supply transformer works in large amplitude alternating magnetic field, it is directly related to the vibration permeability, rather than the initial permeability. When other conditions are the same, the high permeability of the amplitude decreases the magnetizing current. And the PM - shaped magnetic core is a small constant, which is advantageous to the transformer.

The center column of the PM shaped magnetic core is round, for the winding, the winding turn length of the given section area can be reduced, and the copper loss can be reduced.

The PM core area of the window height to width ratio of about 3:1, which can reduce the leakage inductance. At the same time, the ratio of the heat dissipation area and the volume of the magnetic core is larger, which is beneficial to the heat dissipation of the magnetic core.

Discussion on effective parameters of 4 magnetic cores

Calculation of the effective parameters of PM core cores and other closed magnetic circuit, the magnetic core is equivalent, that is to say, the core is replaced by an ideal ring, then according to the formula published by IEC can calculate the effective parameters of PM core set size. We know that the IEC60205 second version of the 2001-04 is provided in the calculation of effective parameters of PM core formula before, there is a trial version, this version of the provisions of the formula in IEC60205 has a different formula, namely the area of A1:

The effective parameters of the PM shaped magnetic core of the same size are calculated by the published formula, and the magnetic cores are measured according to this parameter, and are listed in table 1.

Because the core materials used for the R2K3P material, the properties of materials for i:2300, Pm:83mw/g (100kHz200mT), close to the performance test of the material properties of the magnetic core and the official version of the calculation of the effective parameters of magnetic core and the pilot version of the calculation with the official version of the differences, the Ae value is about 6.5%, the loss is about 11.4%, this is because when the test loss voltage is obtained by the following formula test, the calculation results when measuring the equivalent to the trial version

Test magnetic field increased by 6.5%, the core power dissipation in 100kHz mainly for the hysteresis loss, and hysteresis loss increased with the Bn (n=1.5 ~ 2.5), which leads to the difference between the results of the magnetic core measurements. Therefore, it is very important to calculate the correct magnetic circuit in the use and measurement of the magnetic core.

5 concluding remarks

For a reasonable design of the magnetic core, the key or application, so in the hope that the ferrite production and design personnel to recommend this shape of the magnetic core, so that the device design has a greater choice.