Abstract: Introduced in the switching power supply the common diode restores the question reverse, and to solves take the Buck electric circuit as the example this? The topic commonly used several kind of plans have carried on the comparison.
Key word: Diode; Reverse restoration; Suppresses the plan
Introduction
The high frequency power diode’s is extremely widespread in electric power electronic installation application. But PN ties the power diode, in becomes in the closure state procedure by the breakover, the existence restores the phenomenon reverse. This will cause the diode to lose increases, the circuit efficiency will reduce as well as EMI increases and so on questions. This question is more prominent in the high efficiency power source. The commonly used RC absorption, the string enter switches and so on saturable reactor absorption, soft switching circuit to soften the method to solve, but still not saw about its effect contrast’s research report. This article take the Buck electric circuit as an example, has carried on the comparison to these kind of plans, draws the useful conclusion through the experiment and the simulation.
1 diode restores the principle reverse
Ties the diode take ordinary PN as the example, PN ties which states as follows the current as a result to have the concentration gradient to have the proliferation movement, simultaneously as a result of electric field function existence convective drift, after both balanced, becomes the space charge area in the PN ice formation. When the diode both sides have the forward bias, the space charge area reduces, when the diode both sides have the reverse bias, space charge area broaden. _ when diode in daotong conducting state under impact fanxiang reverse voltage, the save electric charge to one’s own side region or bond in the electric field affect next time, like this then produce one fanxiang reverse electrical current.
2 solution power diode restores reverse several methods
Restored the question for the solution power diode already to present very many kind of plans reverse. One kind of mentality is embarks from the component itself, seeks for the new material to try hard fundamentally to solve this problem, for instance the silicon carbide diode’s appearance has brought the component revolution dawn, it does not have the problem which nearly restores reverse. Another kind of mentality is from analysis situs angle embarking, through increases certain components or the auxiliary circuit makes the power diode to restore reverse obtains the conditioning. At present, the silicon carbide diode not yet massively enters practical, it high cost has restricted the popularization application, what applies massively is under the second kind of mentality softened electric circuit. This article take a 36V input, the 30V/30A output, the turn-on frequency as the 62.5kHz electric circuit (as shown in Figure 1) is an example, softened the method compared with several kind of switches.
2.1 RC absorptions
This is solves the power diode to restore the question reverse the commonly used method. Power diode which works under high frequency, must consider the stray parameter. Figure 2(a) is the electric circuit model, D is the ideal diode, Lp is the lead inductance, Cj is the junction capacitance, Rp is the shunt resistance (high resistance number), Rs is the lead wire resistance. RC absorbing circuit like chart 2 (b) shows, after C1 and R1 series, parallel to power diode D0 on. When diode reverse shutdown, in parasitic inductance’s energy to the parasitic capacity charge, meanwhile to absorbs the electric capacity C1 charge through dead resistance R1. In the absorption similar energy’s situation, absorbs the electric capacity to be bigger, the above voltage is smaller; When diode fast forward breakover, C1 through the R1 electric discharge, the energy majority will consume on R1.
2.2 series saturable reactors
This solves this question another commonly used method, like Figure 2 (c) shows. Generally the ferrites (Ferrite) magnetism link and the crystalless alloy (Amorphous) material’s magnetism link may make the saturable reactor. According to literature [1], when reverse restores the question with the saturable reactor solution diode, the commonly used manganese zinc ferrites have the effect, but the energy loss is bigger than the crystalless material. Along with the material technology’s progress, the crystalless saturated magnetic material performance had the very big enhancement in recent years. This article has selected the Toshiba Corporation’s crystalless material magnetism link (the model: MT12×8×4.5W) circles 2 circles to be full and reactor.
Corresponding chart 3 (a) and Figure 3 (b),ⅠThe stage passes D0 the electric current to be very big, reactor Ls is saturated, the inductance value is very small; ⅡWhen the stage the diode electric current starts drops, Ls was still very small; ⅢThe stage diode current reversal, the reverse recovery procedure starts (trr is restores time reverse), the Ls value increased very quickly, has suppressed reverse recovery current enlargement, like this caused the electric current to turn the di/dt small soft restoration, caused diode’s loss to reduce, simultaneously has suppressed an important noise source; ⅣThe stage diode resumed the conclusion reverse; ⅤStage diode once more breakover, because the electric current increases, Ls very quick saturated.
2.3 soft switching circuits
Figure 2 (d) is one kind of effective diode restores softened electric circuit [2] reverse. Lk is the transformer leakage inductance. n is the transformer ratio-turn, here takes n=3, its work process as shown in Figure 4.
Stage 1 as shown in Figure 4(a), switch S already the breakover, D0 was at the reverse closure condition, excitation inductance Lm and leakage inductance Lk by the linear charge. Stage 2 switch S shuts off, S parasitic capacity Cp charges, this process is very short, but regards as the linearity approximately, as shown in Figure 4(b). Stage 3D0 and the Db even breakover, as shown in Figure 4(c). In the stage 4 diode D0 electric current under the leakage inductance Lk function the drop is 0 gradually, as shown in Figure 4(d). The stage 5 switch S breakover, like Figure 4 (e) shows, in the leg diode Db electric current continues to drop, before S shuts off the drop is 0.
Figure 4(c) D0 breakover, uD0≈0, when to Figure 4(d) the condition, uD0=-u2=u0/(1 n), Figure 5(d) experimental profile has confirmed this point.
3 experimental results
Figure 5 has given in each kind of situation diode D0 terminal voltage profile.
From Figure 5 in the profile may see, the diode restores reverse the voltage burr reduces, explained 3 kind of plans restore reverse to the diode have the suppression effect. With RC absorbing circuit, although has suppressed the diode reverse restoration, but restores reverse the voltage burr and the vibration are also quite obvious. Before after using softens the electric circuit, like analyzes, theoretically the reverse recovery current should reduce to zero, but because in the electric circuit stray parameter’s influence, the diode shuts off in the process the voltage waveform also to have the vibration. The string enters the saturable reactor to restore reverse to the diode suppresses the effect to be best.
4 conclusions
Perhaps the silicon carbide promoted application is the diode restores the question reverse the basic key to the situation. At present mainly uses the RC absorbing circuit. The series saturable reactor as well as the softened electric circuit also suppress the effective plan which the diode restores reverse. The theoretical analysis and the experimental proof, the series crystalless saturable reactor is simplest effectively, obtains further promotion hopefully.
