[MUSIC PLAYING] A few slides before, I told on the true buck boost topology. For smaller power-- let's say below 50 watts-- the SEPIC is a valid topology. A lot of people are afraid of the word SEPIC. That just means single-ended primary-inductance convertor. But let's have a look on the topology itself.
First, we already know the buck topology left-handed. So, converting a higher input voltage to a lower output voltage. If we now move the reference point from anode of the rectifier to the positive output, we see that it's an inverting buck boost that we see right-handed. But it's need to know that we have not longer forward topology.
The buck converter itself is transferring energy to the output when the switch is closed. The inverting buck boost transfers energy to the output when the switch is open. So, here, the inverting buck boost is a true flyback topology. We are going to see this within the next pages.
Let's see if we can get from an inverting buck boost to a true flyback topology. We simply replace, now, the inductor by an ideal coupled inductor. Here, we assume that the leakage is zero-- an ideal coupled inductor.
And left-handed, we got the same circuitry done before-- the same electrical behavior. And if we now change the windings orientation of our coupled inductor and we turn our rectifier, we are able to see that it's a true flyback topology.
The slide before, we already had something that was pretty close to a flyback convertor. If we remember, the switch was high side. And the primary winding of the inductor was low side. But it's a serious connection. Why not change them?
Now, we got the switch low side, and we are pretty close to a flyback topology. Left-handed-- we got the inverting flyback. And right-handed-- if we change the windings orientation of our coupled inductor and we turn the diode, we got the flyback converter that is non-inverting.
Both topologies are non-isolated at the moment. We've got the same ground at input and output. Unfortunately, we've got no ideal elements on the market, so there is a certain leakage at your coupled inductor. It means this leakage will cause you some ringing on your switch. Is there any possibility to get rid of this ringing for a topology with a windings ratio 1 by 1 and non-isolated? We're going to see this within the next page.
So, simply have a look at this. We just put a capacitor from the drain of the MOSFET to anode of the diode. And by a windings ratio 1 by 1, we've got the same voltage level there. So, we are clamping the voltage there.
The benefit of this is we've got a nice [INAUDIBLE] on the primary and secondary site. No more ringing like you are used to at the flyback.
So, don't be afraid of SEPIC. Don't be afraid of SEPIC. Don't be afraid of Cuk. These are just words. Basically, it's a flyback topology with a nice clamping.
There is a difference at the input current. There is a difference at the output current. We're going to see this within the next pages. But please don't be afraid of the word SEPIC or Cuk. They are nice topologies, and well-suited for the low power range below 50 watts. [音乐播放] 几个幻灯片之前，我曾介绍过 真正的降压-升压拓扑。 对于较小的功率， 比如低于 50 瓦， SEPIC 是一种有效的拓扑。 很多人谈 SEPIC 一词色变。 它只是表示单端 初级电感转换器。 但让我们看一下 这种拓扑本身。 首先，我们已经知道 左侧的降压拓扑。 因此，将较高的输入 电压转换为较低的输出 电压。 如果我们现在 将基准点 从整流器正极 移动到正输出， 我们会看到， 它就是我们 在右侧看到的反向降压-升压拓扑。 但需要知道， 我们使用的 不再是正向拓扑。 当开关闭合时， 降压转换器本身 向输出端 传输能量。 当开关断开时， 反向降压-升压拓扑 将能量传输 到输出端。 因此，此处的 反向降压-升压 是真正的反激式拓扑。 我们将在下几页中 对此进行探讨。 让我们看看是否能 将反向降压-升压 变成真正的反激式拓扑。 现在，我们只需 将电感器替换为 理想耦合的电感器。 此处，我们假设 泄漏为零， 即理想耦合电感器。 左侧是以前探 讨过的同一 电路，具有相同的 电气特性。 如果我们现在 更改耦合电感器的 绕组方向并 倒转整流器， 我们可以看到，它是一个 真正的反激式拓扑。 在前面的幻灯片中， 我们已经探讨过 非常接近于反激式 转换器的器件。 如果您还记得， 开关是高侧。 电感器的初级 绕组是低侧。 但它是一种串联。 为什么不改变它们呢？ 现在，开关为 低侧，非常 接近于反激式拓扑。 左侧是 反向反激式。 在右侧，如果 我们更改耦合电感器的 绕组方向并 倒转二极管， 就会得到非反向的 反激式转换器。 此时，两种拓扑 都是非隔离式。 我们在输入和输出端 具有同一个接地。 遗憾的是， 市场上没有理想元件， 因此，耦合电感器 有一定的泄漏。 这意味着此泄漏 将在开关上 导致一定程度的振铃。 对于绕组比为 1 比 1 且为非隔离式的拓扑， 有没有任何可能 消除这种振铃？ 我们将在下一页中 对此进行探讨。 因此，只要简单了解一下即可。 我们只是在 MOSFET 的 漏极到二极管的阳极之间 放置一个电容器。 在绕组比为 1 比 1 的 情况下，我们 在那里得到 相同的电压等级。 因此，我们将钳制 那里的电压。 其优势在于， 我们在初级 和次级侧得到 非常好的 [听不清]。 不再有反激式通常 所具有的振铃。 因此，不要害怕 SEPIC。 不要害怕 SEPIC。 不要害怕 Cuk。 这些只是词汇。 基本来说，它是一种具有非常好 钳位功能的反激式拓扑。 输入电流 存在差异。 输出电流 存在差异。 我们将在下几页中 对此进行探讨。 但请不要害怕 SEPIC 或 Cuk 词语。 它们是非常好的拓扑， 非常适用于 50 瓦以下的 低功率范围。 This website is under heavy load (queue full) We're sorry, too many people are accessing this website at the same time. We're working on this problem. Please try again later.
