LC filter parameter selection

乱世煮酒论天下

LC filter parameter selection [Copy link]

In push-pull and forward converters, the secondary side uses LC filtering, or even LCL or CLC filtering.
How are the inductor and capacitor parameters selected when using these filtering methods? What factors are they based on? I can think of several influencing factors, such as the switching frequency of the primary switch tube, the primary-to-secondary transformation ratio, and the secondary voltage. I haven't thought of any other factors yet.

qwqwqw2088

"In push-pull and forward converters, the secondary side uses LC filtering, which can even be LCL or CLC filtering."

How do you know it's so clear?

乱世煮酒论天下

qwqwqw2088 posted on 2024-3-6 07:48 "In push-pull and forward converters, the secondary side uses LC filtering, and can even be LCL or CLC filtering." It is so clear...

I read it in the book, but it didn't tell me how to choose the parameters?

maychang

[In push-pull and forward converters, the secondary side uses LC filtering, and can even be LCL or CLC filtering]

For all forward converters, the secondary side of the transformer cannot use CLC filtering, and must use L input filtering.

maychang

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-3-6 08:18 I read it in a book, but it didn't talk about how to choose parameters?

【Read in the book】

It can be seen that this book was read in a hurry.

qwqwqw2088

Reading books should be systematic, especially power design, which is quite technical and cannot be fragmented.

qwqwqw2088

I want to say something. In the so-called forward converter, LC filtering is used on the secondary side. That's because the transformer transfers energy, and the energy storage is the inductor after the secondary side rectification. The principle of the forward converter is basically the same as that of the BUCK circuit. A transformer is added between the power switch and the LC filter to increase or decrease the input voltage.

不亦心

Forward topology refers to buck

不亦心

Bu Yixin published on 2024-3-6 09:21 Forward topology refers to buck

To be more precise, it is a forward hard switching topology.

maychang

[I can think of several influencing factors, the switching frequency of the primary switch tube, the primary-to-secondary transformation ratio, and the secondary voltage. I haven't thought of any other factors yet.]

For forward converter circuits (including push-pull, half-bridge, and full-bridge), the most important "influencing factor" of the filter inductance is whether the current in the inductor is continuous. As qwqwqw2088 on the 7th floor said, "The transformer transfers energy, and the energy storage is the inductance after secondary rectification."

The filter inductor has nothing to do with the [primary-secondary voltage ratio]. You are just making wild assumptions without any basis.