第三部分 五种架构的实测效率
06 800→50→12.5 V：67%
所以这是实践层面。我们针对各种情况做了参考设计，现在来比较这些架构。
算法很简单，就是乘法，大家都会算。但你会看到，单看某一级的效率很容易理解：800 转 50，我们能做到 98%；50 转 12，现在能做到 97%，有时还更高；12 V 的 buck，大约 89% 到 90%——目前就是这个水平。
但真正损耗大的地方，是把电流送到这些级之间去的那段配电网络。
如果你今天在展场里走一圈就会发现：即便是现在的 50 V 机架，也有一颗 50 V 转 12 V 的变换器，而它到稳压器之间要走很长一段距离。
所以看今天的方案，这些都是积木：我们做过的 800 转 50 参考设计；50 转 12 有很多选项；12 转到 1 V，可以走分立芯片，也可以走电源模块。
So, this is practice. We've built reference designs for the various cases. And let's compare the architectures. It's very simple — it's multiplication. I think we can all do that. But what you see is it's very easy to understand the efficiency in a given stage. In 800 to 50, we can get 98% efficiency. When you look at 50 to 12, we can get 97, sometimes even higher than that now. With a 12-volt buck converter, around 89, 90%. That's where we are. But where you see there's a whole lot of loss is in that power distribution network along the way, to get that current to those stages. If you walked around the floor today and you looked, you'd say, hey, look, even the 50-volt racks today, there's a 50-V converter that converts to 12 and there's a long distance that it has to travel before you get to your voltage regulators. So, when you look at today, these are the building blocks. I know the expo's closed now, but all these were at our booth. This is a reference design we did for 800 to 50. And then there's a lot of options from 50 to 12. And then these — you can either go discrete with a chip or a power module approach from 12 to 1.
小结 单级效率都在 97–98%，整机却只有 67%——差额全部落在「把电流送到下一级」的那段铜上，而不是落在变换器里。
07 800→50→6.25 V：64% 与 73%
再看下一个选项。我们看 800 转 50，然后看 6 V 这条路：更大的降压比，50 转 6，用 8:1 的 IBC。
这里你会看到几种不同的选择：800 转 50 仍然是 98%，配电网络上的效率仍然很高；50 转 6 我们也能做到 96%、97%。然后你有两条路可选。
现在稳压器上的电压更低了，可以继续用常规的横向送电——低压下跑 buck 没有任何问题——但它同时打开了探索 VPD 的机会。
真正的好处出现在最后一公里：走 VPD 之后配电网络损耗的下降。
VPD 本身的效率会更低：它必须做得很薄，必须跑更高频率；而且因为要大幅减少电容，同样得靠更高频率来换取更高带宽，才能塞到处理器下方。
但收益是清楚的：整体系统效率有明显提升。
Now, looking at the next option. Let's look at 800 to 50 and let's look at the 6-V option. A higher step down going 50 to 6 and 8:1 IBC. You can see here you get some different options. 800 to 50's still 98% efficient, still very high efficiency on the PDN. And then we can still get really high efficiency: 50 to 6, we can get 96, 97% efficiency. And then you can go with two options. Now that I have a lower voltage on my voltage regulator, I can stick with my conventional lateral power — there's no problem running a buck converter at a lower voltage — but it also opens up the opportunity to explore VPD. And where the real benefit comes is when you look at that last mile: the PDN loss reduction when you go to the VPD. The VPD is going to be lower efficiency. Ultimately it's got to be very low profile, you have to go higher frequency, and because you're going to need to reduce a lot of capacitance, it's got to be higher frequency to get higher bandwidth to enable it to go down underneath the processor. But the benefit's clear: you can see a significant improvement in overall system efficiency.
小结 同一串变换器、同一个 6.25 V 母线，只把最后一级从正面挪到背面，整机就从 64% 变成 73%——九个百分点的差距全在 PCB 上，不在芯片里。
08 800→12.5 V：68%
然后看 800 转 12 V。这一条我们做得也不错，变换效率大约 97%。
12 V 之下，配电损耗本来就不大，后面接常规的 12 V buck 就行。
但它又受限于横向送电——那最后一公里会把整体效率拉下来。
And then let's look at the 800 to 12. Again, we can do pretty good. Around 97% efficient is what we can see conversion wise. 12 volts you don't have a whole lot of power distribution losses. And then you stick with your conventional 12-volt buck converters. But again it's limited by the lateral power delivery. So, that last mile is something we see as making that a lower overall efficiency.
小结 800→12 V 单级效率高、12 V 母线损耗也小，但它只能配横向送电——少了一级变换，却被最后一公里追平，最终 68%，卡在中间。
09 800→6.25 V：74%
接下来这一条是走得更远的：800 转 6 V。
思路是你有一颗又长又窄的变换器，这种细长形态把高压直接带进低压域。我这里讲的是电气层面。
电气上它允许你——效率大约 95%。
而且它的配电损耗很低，因为你把变换器物理上挪得离负载更近了。
然后你可以用它驱动 VPD。整体算下来，端到端效率大约 74%。这是我们在一套 20 kW 输入的系统上预期的结果。
右边第一张图就是带 VPD 的那种形态——低高度设计。
And then what we say here is this is going further: 800 to 6. The idea is that you've got this very long skinny type converter, this skinny type design. It's bringing the high voltage into the low voltage domain. I'm talking about from an electrical perspective here. Electrically it allows you — and then you can get around 95% efficiency. And again it's got pretty low PDN losses because you're bringing that closer physically to your load. And then you can use it and drive a VPD. And overall that gives us around 74% end-to-end efficiency. That's kind of what we expect on a 20 kW type system input. And you can see this is the first one on the right here where we've got a VPD type thing — a low profile type design.
小结 800→6 V 的单级效率只有 95%，是四条路里最低的，整机 74% 却是最高——「单级效率」和「系统效率」在这里第一次分家。
10 800→50→1.8-5 V：73%
最后这一条我称之为「糊涂账」（cloudy math），因为它更前瞻：你可以说，我们很多人其实并不想把高压放得离处理器那么近。
所以你可能会说：那就守住 800 转 50，守住功率分配板，然后从 50 V 走到——我说这是个很宽的范围，这个领域有很多人在做，德州仪器也在内——我们并不确定最优母线电压是多少，大概在 1.8 V 到 5 V 之间。
那会落在类似「基板内嵌 VR」的位置，再往后可以走向 IVR 那样的方案。它有前景，但更远。
所以从电气角度，我们看到两条领先路线，是我们认为从 800 V 到负载最高效的方式。
一条就是我们熟悉的「分而治之」：功率电子这几十年一直在分级、在把每一级优化到极致。而且多加一级并不会把效率拉低太多，因为我们已经不在低效率区间了——98%、97%、96%，这些变换级的效率非常高。
但话说回来，能减少级数这件事，仍然是有价值的。
And then this one I'll call this cloudy math. It's kind of forward looking, where you can say, well, maybe I don't want to put — as a lot of us know, we don't want to put high voltage so close to our processor. So, maybe you say we stick with our 800 to 50, we can stick with our power distribution board, and then we can go 50 to — I'll say it's a wide range, there's a lot of different people working in this area, TI included, where we say we're not sure the optimal bus voltage. It's somewhere between 1.8 and 5 volts. And that's going to be somewhere like a substrate-embedded VR. And then you can go to like an IVR type solution. And that's got promise, but it's further looking out. So, we kind of see two leaders from an electrical perspective that we think will be the most efficient ways to get from 800 volts to load. And that's your conventional divide and conquer, like we're used to. In power electronics, we've been dividing and conquering and optimizing our stages. And again, adding more stages doesn't reduce your efficiency too much, because we're getting to such high efficiency. We're not talking low-efficiency designs anymore. We're talking 98%, 97, 96. They're very high efficiency, these power conversion stages. But the idea of being able to reduce the stage, that still has a benefit.
小结 两条路线其实是同一条曲线上的两个点：级数可以加，因为每级都已是 97–98%；但只要最后一公里还在板上横着走，加级数的收益就吃不满。
（转自公众号：一超一世界）
