SAGAQWE

那我們就在這帖有關主題下, 大家心平氣和, 嘻嘻哈哈的說說共模干擾在隔離變壓器內的話題吧..
早前你問.. 我知不知有關這層x屏蔽, 能減底共模干擾的noise, 我是真的不知道.
因為..
在業界, 99%的產品, 也沒有這措施, 也沒清楚制定..
總之你要帶有這層屏蔽的話, 我給你做, 價錢大約是高20%, 但別問能逹什麼效果, 衰減多少XX單位, (究竟它用什麼單位的呢?)... 這有點像, 某領導所講, 你信不信, 總之我就信了一樣.. 我也曾說笑要求朋友繞個初次級絞合混繞的炸彈, 但最終只得到白眼一雙, 換來句你想死不如交流直接整流吧..
共模干擾, 電流過2個平行導體時便有, 這差不多就像電流流經導體會發熱, 亞媽是女人一樣的普通..  

所以我也很想聽聽小兄弟, 有關在變壓器繞組內減低共模干擾的方法..

PheniX01

那我們就在這帖有關主題下, 大家心平氣和, 嘻嘻哈哈的說說共模干擾在隔離變壓器內的話題吧..
早前你問..  ...
SAGAQWE 發表於 2017-5-28 18:54

Interesting, just by searching "electrostatic shield transformer" in Google, you can already find a bunch of information about this, there is even a document about a research of this published by schneider-electric!

同埋其實我無燥過，我係唔明點解你會覺得Faraday's cage係一種安全措施同block唔到noise，明明Faraday's cage提得最多嘅就係block RF，間間博物館都有喎

PheniX01

那我們就在這帖有關主題下, 大家心平氣和, 嘻嘻哈哈的說說共模干擾在隔離變壓器內的話題吧..
早前你問..  ...
SAGAQWE 發表於 2017-5-28 18:54

上digikey搵isolation transformer，第一隻牛已經有electrostatic shield，唔洗訂製，好common喎
http://catalog.triadmagnetics.com/Asset/N-67A.pdf

SAGAQWE

冇錯呀, 你可搵到有, 也可以訂做時要求加入, 但就如同我之前所講, 這沒有標準的, 也非通用必須的, 你看看它的PDF, 它也沒提及這層shield的作用.  

火牛, 會注重佢嘅電磁干擾, 影響鄰近的電路, 比小兄弟所注重的共模干擾, 初次級間的noise更多, 而降低電磁干擾, 一喺放到冇雷公咁遠, 又或有高要求就買隻全密封嘅牛...  就等如我最初說笑, 看到些DIY用上些銅片或錫紙在火牛身上黐黐貼貼, 說成加強屏蔽..

共模干擾併不是線包插入片金屬在中間再接地便能完全消除, 將noise帶入地去, 這日後當你看到有DIYER, 刻意空接這根線不作處理時, 問問便知點解.

PheniX01

冇錯呀, 你可搵到有, 也可以訂做時要求加入, 但就如同我之前所講, 這沒有標準的, 也非通用必須的, 你看看它 ...
SAGAQWE 發表於 2017-5-28 22:21

https://www.hammfg.com/electronics/transformers/line/169s.pdf
How about this one? Isolation transformers from schneider-electric also have this.
Actually, I cannot find one without grounded shielding. It seems like the one without is customized, not the one with it.

SAGAQWE

明天上班了, 沒時間磨在這裡, 不如就朋友這火牛共模干擾, 給你個問題想想...
"在火牛初級上接個Y電容會變成怎樣"

PheniX01

明天上班了, 沒時間磨在這裡, 不如就朋友這火牛共模干擾, 給你個問題想想...
"在火牛初級上接個Y電容會變 ...
SAGAQWE 發表於 2017-5-28 23:01

I know how to suppress common mode and differential mode noise, it is stated clearly in a document published by murata. But it doesn't mean that electrostatic shield is useless. I have already told you schneider-electric has a document about this, why don't you go have a look and see the actual attenuation value?

PheniX01

I just found that actually the page "isolation transformer" from wikipedia has stated this clearly.
Quote from wiki:
Isolation transformers are designed with attention to capacitive coupling between the two windings. The capacitance between primary and secondary windings would also couple AC current from the primary to the secondary. A grounded Faraday shield between the primary and the secondary greatly reduces the coupling of common-mode noise.

Though, I admit that wikipedia is not a authoritative source of information.

PheniX01

冇錯呀, 你可搵到有, 也可以訂做時要求加入, 但就如同我之前所講, 這沒有標準的, 也非通用必須的, 你看看它 ...
SAGAQWE 發表於 2017-5-28 22:21

btw, there is NO solution that can completely remove noises. All different solution has different frequency response, again, go check the document from schneider-electric.

gapson

Parasitic is not only 50/60Hz current; its a wide band signal. Keeping low impedance on Earth is very important.

For whatever reasons, any so called shields, EMI filtering, shall be linked to the earth. As a DIYer, it would be a great opportunity to make proper grounding and even better (or worse) grounding than some consumer electronics.