Application of pyromagnetic integration technology

Application of magnetic integration technology in current doubling synchronous rectifier

in order to solve the problem of more magnetic components and connecting terminals in the traditional current doubling synchronous rectifier converter, the integrated magnetism technology has been applied in this topology. Several magnetic integrated current doubler rectifying topologies are analyzed and compared. Finally, China's cathode materials account for 43.77% of the global market. The experimental model and waveform of 1V, 20W DC/DC converter are given

key words: current doubling rectifier; Magnetic integration; Topology

0 introduction

in today's high current dc/dc converters, current doubling rectifier (CDR) topology has become the optimal output rectifier topology choice because of its own characteristics. Compared with the traditional rectifier topology with intermediate tap, the secondary side of the transformer has only one set of windings, which is relatively simple in structure; At the same time, the number of turns of CDR secondary winding is also less, and the loss of secondary winding will be reduced under the condition of high current; And its output has two filter inductors, and the current flowing through each inductor is only half of the load current. Therefore, the power loss on the output filter inductor is also small. Due to the existence of two filter inductors, the output current/voltage ripple of the converter is also relatively small. However, it requires three magnetic elements, which will inevitably lead to the increase of volume, thereby reducing the power density; At the same time, there are many connection terminals. When the current is large, the power loss on the connection terminals must be relatively large. In order to overcome the above shortcomings, integrated magnetism technology has been applied in CDR topology for a long time. The so-called magnetic integration is to wind two or more discrete magnetic components (transformer gb/t11352 (2) 009 "general engineering cast carbon steel parts", input/output filter inductors) in a pair of magnetic cores in the converter, so as to achieve the purpose of reducing volume, improving power density and reducing connection terminals

this paper analyzes and compares various magnetic integrated current doubler rectifier topologies (IM CDR), selects the better one, and based on this im CDR topology, experiments are carried out on a dc/dc converter with an output of 1V and 20W, and the experimental waveforms are given. In particular, when the load is large, the energy stored in the leakage inductance of the primary side of the transformer can be used to realize the self drive of the secondary side synchronous rectifier, thereby reducing the complexity of the control circuit

1 Comparison of several magnetic integrated current doubler rectifier topologies

Figure 1 shows several IM-CDR topologies suitable for low voltage high current voltage regulation module (VRM) topologies so far

(a) current doubling rectifier of discrete magnetic elements (b) im-cdr[1] proposed by pengc (c) im-cdr[2]

(d) (c) the air gap of the intermediate column in Chen Wei's im-cdr[3] (E) im-cdr[3] proposed by Xupeng (f) improved IM-CDR

proposed by SunJian figure 1 IM-CDR circuit structure

Figure 1 (a) shows a CDR circuit composed of discrete elements, which requires a total of three discrete magnetic elements, namely, output.Filter inductors L1 and L2, and transformers. As a result, the volume and weight of the converter are too large. At the same time, it has many high current connection terminals, which will inevitably increase the conduction loss of the secondary side

in order to avoid the above shortcomings of the traditional CDR topology in China, the world's largest rubber market, pengc proposed an IM-CDR circuit topology [1], as shown in Figure 1 (b). It winds the three discrete magnetic elements (output filter inductance and transformer) in the same pair of magnetic cores in the previous CDR rectifier circuit, which greatly reduces the volume and weight of the converter. However, due to the large number of windings and connecting terminals on its secondary side, the application of this CDR topology is limited

Figure 1 (c) is the CDR topology proposed by Chen Wei [2]. It is to decompose the secondary winding of the transformer in Figure 1 (b) and wind it on the two outer magnetic columns of the magnetic core respectively. As a result, the structure of the secondary side of the topology becomes simple, and the connection terminals are relatively reduced. This CDR topology is very suitable for the application of high current converters, because it contains fewer connection terminals and windings. And because there is an air gap on its central magnetic column, the excitation inductance LM on the primary side will be reduced, and the ZVS of the main switch can be realized when the output load is light [2]. However, the air gap cannot be opened too large. If it is too large, LM will be very small, resulting in the increase of excitation current on the primary side of the transformer, thereby increasing the conduction loss on the primary side

Figure 1 (d) shows the situation that the central column does not open the air gap. At this time, the excitation inductance LM of the primary side of the transformer is large, and the excitation current in the primary side winding is small. Therefore, the conduction loss of the primary side is also small. In this IM-CDR topology, because the primary and secondary side windings are wound on three magnetic pillars respectively, the coupling between the primary and secondary side windings is poor, resulting in large leakage inductance at the primary side of the transformer and reducing the performance of the converter. In addition, the IM-CDR topology with no air gap in the middle and air gaps on both sides makes the production of its magnetic core more difficult. There is no air gap on the two outer magnetic columns of the ordinary EE or EI core. To be applied to the IM-CDR topology in Figure 1 (d), air gap must be added to the outer magnetic column, which makes it difficult to realize

xu Peng proposed the IM-CDR circuit topology as shown in Figure 1 (E) [3]. It is to split the primary side winding of the transformer in Figure 1 (d) and wind it on the two outer magnetic columns of the magnetic core respectively, so that the primary and secondary side windings will form a better coupling. And only add air gap on the central magnetic column, and no air gap on the two outer magnetic columns. The improved IM-CDR not only reduces the primary leakage inductance of the transformer and improves the performance of the converter, but also this magnetic core structure is more convenient for production. Ordinary EE and EI magnetic cores can meet the requirements, and it is also conducive to reducing core loss and improving efficiency [3]. However, there are two groups of windings on its primary side, and its structure is more complex than that in Figure 1 (c) and figure 1 (d)

the same problem exists in these IM-CDR topologies proposed above, that is, their output filter inductance is limited, so there is a relatively large output current/voltage ripple. Therefore, Sun Jian proposed a circuit as shown in Figure 1 (f). Compared with figure 1 (E) in structure, only a group of windings are added to the central magnetic column and connected in series at the output end, which is equivalent to adding an additional filter inductor at the output end, thus reducing the output current and voltage ripple [4]. However, this topology is not suitable for low voltage and high current occasions

to sum up, the IM-CDR topology shown in Figure 1 (c) is the simplest, and it is the most suitable for high current converters that do not require very high output current/voltage ripple. Although the primary side of the transformer has relatively large leakage inductance, it is still the best choice for compromise. Moreover, when the load current is large, the transformer leakage inductance can be used to realize the self drive of the secondary side synchronous rectifier

2 experiment and its results

im CDR structure selection is shown in Figure 1 (c). It can be seen from the structure that the same air gap (LG) is added to the three magnetic columns of the magnetic core, which will inevitably lead to the increase of the leakage inductance (LK) on the primary side of the transformer, but the energy in the leakage inductance on the primary side of the transformer can be used to realize the self driving (opening) of the secondary side synchronous rectifier, and the shutdown of the synchronous tube is completed by adding a driving signal. The experimental circuit is shown in Figure 2. It can be seen from Figure 2 that the driving circuit of the secondary side synchronous tube includes a winding (NA), two diodes (DA1, DA2) and two MOS tubes (SA1, SA2). Its implementation is relatively simple, and it only needs to add a group of windings on the central pole of the magnetic core. The primary side of the transformer adopts a symmetrical half bridge topology. The specific parameters of the experimental circuit are listed in Table 1. The experimental waveforms are shown in Figure 3 and Figure 4. Figure 3 is the waveform of the primary voltage of the transformer and the gate drive voltage of the two synchronous rectifiers measured when the load current io=4a. Because the load current is small at this time, the excitation current reflected on the primary side of the transformer is also small. At the moment when the primary side switch is turned off, the key influencing factor of voltage transformation and diversification of raw material structure is that the oscillation peak between the primary side leakage inductance (LK) of the oil purifier and the output junction capacitance (CO1, CO2) of the switch is not high enough to open the synchronous rectifier on the secondary side. Therefore, during the period when both primary switches are in the off state, the body diode of one of the synchronous rectifiers must be connected for continuous current. At this time, the load current is not large, and the power loss on the body diode is not obvious. With the increase of load, the oscillation of the primary side will gradually increase until the secondary side synchronous rectifier can be opened. Figure 4 shows the voltage waveform at the primary side of the transformer and the driving waveform of the two synchronous tubes when the load current io=20a. When the primary switch is turned off, the energy in the leakage inductance is enough to turn on two synchronous tubes. However, the shutdown of the synchronous tube can only be realized by adding a driving signal. They come from the gate drive Vg1 and VG2 of the primary switch respectively. Figure 5 is the measured efficiency curve of the converter

Table 1 experimental circuit parameters

Figure 2 experimental circuit diagram

Figure 3 VP, vg3 and vg4 waveforms when io=4a

Figure 4 VP, vg3 and vg4 waveforms when io=20a

Figure 5 converter efficiency curve

3 conclusion

current doubling synchronous rectification topology is more and more widely used in high current converters. However, the traditional structure has many shortcomings, such as magnetic components and large volume. In order to overcome these shortcomings,the, Magnetic integration technology has been applied in this topology for a long time. This paper analyzes and compares several magnetic integrated current doubling rectifier topologies, and gives the corresponding experimental circuit model. In case of heavy load, the energy stored in the leakage inductance of the primary side of the transformer can be used to realize the self drive (on) of the secondary side synchronous rectifier