Author Topic: LM399 based 10 V reference  (Read 536644 times)

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Offline Kleinstein

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Re: LM399 based 10 V reference
« Reply #1375 on: Yesterday at 05:00:02 pm »
The common mode choke would mainly act on the common mode signal, e.g. to filter a so perfectly isolating DCDC converter and reduce an injected signal from there. The output regulation is much less effected (the CM mode chokes still have some differential mode inductance) and can still be fast (e.g. with somewhat transisent loads).
With separate inductors the filtering would also effect the output drive / regulation speed. Transient loads may lead to more LC ringing and slow regulation. This could be an issue with separate drive an sense terminals.
 
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Offline dietert1

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Re: LM399 based 10 V reference
« Reply #1376 on: Yesterday at 05:06:58 pm »
Common mode filters are usually made with high inductance cores that are less useful for making chokes as they easily saturate. So a typical inductance for chokes like those in the image is 10 to 100 uH, while a typical common mode choke is at 5 or 10 mH.
I am sometimes using Würth 744866104 common mode chokes with 100 mH. Those have a stray inductance of about 1 mH.

Regards, Dieter
 
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Online iMo

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Re: LM399 based 10 V reference
« Reply #1377 on: Yesterday at 05:48:36 pm »
..What is the difference between using a PI bifilar common mode filter on the output vs. using separate cores for each wire like in older voltage standards..

Provided all three coils are perfectly identical (incl the winding direction) there is none difference.
As on your above shot the proper way would be to use single toroidal core with trifilar winding. Also the return path wire (ie gnd) must be included (the number of wires/signals in the single CM choke is unlimited, ie you may pass entire flat cable with say 100 different signals and their returns through a single CM choke).
« Last Edit: Yesterday at 05:57:05 pm by iMo »
 
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Offline argintviu

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Re: LM399 based 10 V reference
« Reply #1378 on: Yesterday at 06:05:50 pm »
Ah, that's good to know. So I can put the 10V, 7V and GND signals through a single choke instead of using 2 (i.e. 10V and GND on one core and 7V and GND on another). Helps save a few parts.
« Last Edit: Yesterday at 06:07:21 pm by argintviu »
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Offline Kleinstein

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Re: LM399 based 10 V reference
« Reply #1379 on: Yesterday at 09:50:22 pm »
..What is the difference between using a PI bifilar common mode filter on the output vs. using separate cores for each wire like in older voltage standards..

Provided all three coils are perfectly identical (incl the winding direction) there is none difference.
3 separate coils are different. They could have the same effect on the common mode signal, but the effect on a differential signal is quite different, with much more inductance seen to the differential signal.
Separate coils (especially if not identical) also tend to have stronger coupling from the CM to the differential signal.
 


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