Raise 48V to come further the efficiency of plan of 12V power source
[introduction]48V distribution is very common in data center and communication application, the solution that has a lot of differring can reach 48 V step-down intermediate voltage course. The simplest method may be step-down develop attacks, it can be offerred high-powered, but power density often is not worth. Use coupling inductance upgrades polyphase step-down converter can increase power density considerably, this kind of plan and advanced replacement scheme are about the same, held huge performance dominant position at the same time. Between the winding of polyphase coupling inductance retrorse coupling, consequently the voltaic ripple in each phase current can offset each other. This kind of advantage can use the improvement that exchanges efficiency,
48V distribution is very common in data center and communication application, the solution that has a lot of differring can reach 48 V step-down intermediate voltage course. The simplest method may be step-down develop attacks, it can be offerred high-powered, but power density often is not worth. Use coupling inductance upgrades polyphase step-down converter can increase power density considerably, this kind of plan and advanced replacement scheme are about the same, held huge performance dominant position at the same time. Between the winding of polyphase coupling inductance retrorse coupling, consequently the voltaic ripple in each phase current can offset each other. This kind of advantage can use the improvement that exchanges efficiency, or of dimension reduce and of power density rise etc. The article introduced a give typical examples, the bulk of its magnetism component and weight have original 1/4 only, make the occupation standard dimension that 1.2 KW solution accords with 1/8 brick, and prep above of peak value efficiency 98% . The article still discussed mainly how the quality factor according to coupling inductance (FOM) optimizes 48 V develop to attack.
48V distribution course connects regular meeting step-down to come a certain voltage intermediate, often be 12 V or lower, this locality load that differs next nods manostat to offer all sorts of different voltage to different load directly. Come to 48 V adjuster of 12 V step-down, one of first selection are polyphase step-down converter (graph 1) . This kind of solution provides stabilized voltage VO and performance of swift transient state, come true very easily and cost is inferior. Arrive to hundreds of tile > the power limits of 1 KW, can consider 4 photographs paralell connection. However, efficient it is element of a first consideration normally, with 12 V even the inferior voltage application that 5 V inputs is compared, 48 V converter to carry low switch loss, switch frequency normally relatively inferior. This meeting is in respect of ” of second of ” volt × is caused to magnetism component double damage, also meet because of already apparent voltage the time with relatively longer action. Accordingly, apply photograph comparing with inferior voltage, the magnetism component of 48 V volume is normally larger, the ” of second of ” volt × that uses much more v/LIT all over the ground winding to bear to rise significantly. Converter of 48 V step-down still can come true efficient, but integral dimension comparatives normally big, among them inductance held major bulk.
Basic 48 V has 4 looks to converter of step-down of 12 V ~1 KW, inductance of schism of H of μ of use 6.8, switch frequency is 200kHz. These 4 inductance are current the biggest with highest component, occupy the much of solution bulk. The target of the article is what maintain or raise implementation of this initiative design place is efficient, but the size that reduces magnetism component significantly.
Groovy step-down converter the voltaic ripple of each photograph but by formula 1 beg piece, occupy sky comparing to be D = VO/VIN among them, VO is output voltage, VIN is input voltage, l is inductance value, fs is switch frequency.
Graph 1. The converter of 4 photographs step-down of use schism inductance.
The feeling that use leakage is Lk and mutual inductance replaces schism inductance for the coupling inductance of Lm (DL) , CL (coupling inductance) medium voltaic ripple can express to be formula 2. FOM expresses to be formula 3, among them Nph is counted for coupling photograph, ρ is coupling coefficient (formulary 4) , j is moving index, define the applicable interval that occupies sky comparing only (formulary 5) .
The FOM curve that improvement the first condition is Nph = 4 of scale of a few when be aimed at coupling coefficient Lm/Lk actual and reasonable values (graph 2) . Gules curve Lm/Lk = 0 represents the base line of FOM = 1 of schism inductance. Had proved, leakage feels CL (NCL) structure can realize low-down defect wave commonly very tall Lm/Lk, FOM cost is very accordingly high also. However, although the target falls to occupy sky comparing as it happens to be located in D = 12 V/48 V=0.25 of wave of the first defect in good case, but a certain limits that is necessary to consider VIN and VO. Occasionally, nominal VIN can be 48 V or 54 V increase on a few tolerance, VO can be adjusted to be far from 12 V, etc. If occupy sky comparing to change inside a certain limits near D = 0.25, to make voltaic ripple is restrained from beginning to end, the typical CL that should choose to have quite big leakage to feel is designed, is not NCL, but FOM value is quite great still. Hypothesis Lm/Lk>4, compare with photograph of DL base line, the inductance value in reducing CL may make pursue 2 medium FOM raise about 6 times. Reduce energy memory to be able to affect needs magnetism component bulk directly. Accordingly, reduce H of μ of DL = 6.8 should be helpful for reducing size for H of μ of CL = 1.1.
Graph 2. Be aimed at value of a few different Lm/Lk, the FOM of 4 photographs CL and the function that take sky comparing D concern. Outstanding showed target extent.
Graph 3. H of μ of DL = 6.8 and H For of μ of 1.1 of × of CL = 4 (VIN = 48 V and Fs = 200 KHz) the function of the voltaic ripple when and VO concerns. Outstanding showed target extent.
Graph 3 showed corresponding voltaic ripple, the H (Lm = 4.9 of μ of 1.1 of × of 4 photographs CL = 4 of the H of μ of DL = 6.8 of base line design that compared VIN = 48 V and condition of Fs = 200 KHz to fall and proposal μ H) ) . In target area, similar or the voltaic ripple of the voltaic ripple of CL and DL is smaller. This means the likeness of root mean square of all circuit weaveform, conduct loss similar also. The identical ripple when identical Fs still means switch loss, grid drive loss to wait identical also, because the efficiency of these two kinds of solutions should be very similar (the contribution of hypothesis DL and CL inductance loss is similar, this is exclusive distinction) .
Graph 4. Inductance of H of μ of 4 DL = 6.8 (upper part) be replaced to be H of μ of 1.1 of × of CL = 4 (lower part) , bulk reduces original 1/4.
Graph 5. 48 V adjusts to 12 V the first class. Component places the 1/4 brick outline in PCB front inside. Component of will all ~1 Mm moves to bottom: 1/8 brick.
Graph the H of 4 μ of 1.1 of × of CL = 4 that showed a design, its replaced inductance of H of μ of 4 DL = 6.8. The dimension of every 5 DL is × 16 Mm of 28 Mm of × of 28 Mm, assume their those lies between 0.5 Mm here, so the 4 photographs CL that dimension is × 12.6 Mm of 18 Mm of × of 56.5 Mm can make magnetism component bulk reduces original 1/4. Graph 5 showed complete 1.2 KW 48 V comes solution of 12 V adjustment, PCB is bosseyed the component that go up is located in inside 1/4 brick outline. CL dimension and enclose a course to be designed technically, two CL component can be put in occupation standard inside 1/4 brick dimension. Component of will all ~1 Mm (capacitance of FET, controller IC, pottery and porcelain) place in PCB bottom, achieve the 1.2 KW solution of 1/8 brick dimension thereby.
Turn into when inductance of H of μ of DL = 6.8 when H of μ of 1.1 of × of CL = 4, the electric current in inductance placed rate limitation to also improve 6 times, this conduces to improvement transient state function. Besides, although magnetism component total volume reduces original 1/4, but the inductance saturation rating when 100 ° C raised about 2 times.
Graph the solutions of 6 VIN = 48 V that showed a proposal (output VO = 12 V) transient state function. Place of no less than expects, to metabolic load current, feedback will output voltage adjustment to come to establish a value beforehand, at the same time compensation inputs any change of voltage.
Graph 6. 75 A is laden rank jump next VO = 12 V to output (the transient state function when H) of μ of 1.1 of × of CL = 4.
The efficiency that achieves is shown 7 times like the graph, it may be first performance data. It and advanced trade solution undertook comparative: 48 V comes 12 V (fixed 4:1Step-down) LLC, primary side and sub side all have matrix transformer and GaN FET. Of 10 implementation be fully loaded with efficiency for 97.6% , and fiducial efficiency is 96.3% . This is meant below full power loss reduces 16.6 W, the solution of the proposal realized the improvement of 1.6 times. When efficiency already such tall when, loss should reduce so big range to come true very hard normally.
The balance between dimension and efficiency is likely of course. Graph 8 compared H of μ of 1.1 of × of CL = 4 (the 1/4 that magnetism component dimension reduces DL) with μ of bigger 3 of × of CL = 4 H (the 1/2 that inductance bulk reduces DL only) efficiency. The H of μ of 3 of × of CL = 4 with physical larger size has H of taller μ of leakage feeling Lk = 3 and bigger mutual inductance Lm = 10 μ H. This makes Fs OK and relaxed reduce to 110 KHz, promote whole load the efficiency inside limits considerably thereby.
Graph 7. Compare to the efficiency of 12 V solution with the advanced 48 V of 1/8 brick dimension.
Graph 8. The proposal 48 V of use coupling inductance comes the efficiency of 12 V solution and dimension balance.
Use the dominant position of coupling inductance, 48 V reduces magnetism component total size the 1/4 of main component inductance to 12 V solution, achieved 1.2 KW power with the 1/8 brick dimension of occupation standard. Reduce in magnetism component dimension 4 times while, it held outstanding efficiency property, electric current of transient state inductance is placed rate raised 6 times, inductance Isat rating raised 2 times.
As advanced as the industry of similar measure 48 V is compared to photograph of 12 V solution, its loss below full power reduced about 1.6 times. If of magnetism component dimension reduce scope need not so big, efficiency still can rise further.
In the meantime, the solution of the proposal offers outstanding stabilized voltage output, can put in the client directly on mother board, use standard silicon FET to optimize cost further. Compare to it, use the 4:1 of blame stabilized voltage of complete GaN FETLLC is made as alone module, make appliance has multilayer, sensitive layout and embedded the special PCB of matrix transformer.
Integral function improves the dominant position that reflected IP of patent of ADI coupling inductance, we are very glad to offer its numerous client to be used at DC-DC application.
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