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Old 3rd March 2010, 08:17 AM   #41
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What was wrong at my question about #33?

I read now only about the weaken and the royal way for rectifier design and the input requirements of swtich mode power supplies (SMPS) - have a look to the headline of this thread

Nevertheless very interesting, unfortunately the wrong subject.

If you want to find this at later times, nobody looks quite certainly about
" Variations of DC Main Filter against buzzing Toroid Transformers - what is the right? "

Last edited by tiefbassuebertr; 3rd March 2010 at 08:20 AM.
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Old 3rd March 2010, 09:41 AM   #42
Bonsai is offline Bonsai  Taiwan
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I work in a place where there is a big lab and a lot of SMPS type work is going on. If you look at the voltage and current waverforms from all sorts of equipment connected to the mains, you see it is very distorted with lots of harmonics (think about triac dimmers, motor speed control, power supplies getting switched on and off - hopefully using FWBR!). These are some of the reasons you get DC on the mains. DC on the mains means for a period of time the positive and negative halves of the supply are not closely balanced - ie.e don't cancel out. Result is a net DC on the supply lines. Thank fully, this normally does not last for too long.
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Old 3rd March 2010, 03:27 PM   #43
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Originally Posted by Bonsai View Post
I work in a place where there is a big lab and a lot of SMPS type work is going on. If you look at the voltage and current waverforms from all sorts of equipment connected to the mains, you see it is very distorted with lots of harmonics (think about triac dimmers, motor speed control, power supplies getting switched on and off - hopefully using FWBR!). These are some of the reasons you get DC on the mains. DC on the mains means for a period of time the positive and negative halves of the supply are not closely balanced - ie.e don't cancel out. Result is a net DC on the supply lines. Thank fully, this normally does not last for too long.
I would aldo suspect that if there is DC on the mains that it would usually be accompaied by lots of second harmonic. So here is an interesting question. We can block the DC by the diode-capacitor means we have discussed here, but that will not do anything about the second harmonic. What will the presence of the second harmonic do to the transformer? We will have an asymmetrical waveform there, with equal area on top and bottom, but different peak voltage values and correspondingly different half-cycle times.

Might it interact with core magnetic nonlinearities to re-create some DC current flow?

What will the presence of significant second harmonic do to the rectification process on the secondary side of the power transformer?

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Bob
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Old 4th March 2010, 03:56 AM   #44
Eva is offline Eva  Spain
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Quote:
Originally Posted by tiefbassuebertr View Post
What was wrong at my question about #33?

I read now only about the weaken and the royal way for rectifier design and the input requirements of swtich mode power supplies (SMPS) - have a look to the headline of this thread

Nevertheless very interesting, unfortunately the wrong subject.

If you want to find this at later times, nobody looks quite certainly about
" Variations of DC Main Filter against buzzing Toroid Transformers - what is the right? "
Do you think that this post is offtopic?

http://www.diyaudio.com/forums/solid...ml#post2105213

Essentially I'm telling that even a pair of back to back diodes and a single electrolytic capacitor are very effective to make toroids quiet, and I'm demonstrating it with waveforms captured from oscilloscope.
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Old 4th March 2010, 11:26 AM   #45
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Quote:
Originally Posted by AndrewT View Post
I have thrown away a few old televisions and replaced the internal fuse in a couple of others.
All of them used halfwave rectification.
Slow charge was handled by thermistor in every case.
It was usually done that way in old live chassis television receivers so that the internal ground could be connected to neutral. It made them a little bit less dangerous to service without an isolating transformer and would also help combat capacitive hum pickup. Usually a non-isolated switching or linear regulator was used to feed the horizontal deflection circuit directly. Auxillary power supplies could be derived either from the flyback transformer in the horizontal deflection circuit, the inductor of the switching regulator, if it used one, or from a small line frequency transformer.

Modern TV:s don't use half wave rectification as they have switched over to isolated SMPS power supplies. It's hard to make a live-chassis receiver when you need AV inputs and outputs. Usually the only interconnections on live-chassis ones were a capacitor isolated RF input and sometimes a transformer isolated headphone output.

Last edited by megajocke; 4th March 2010 at 11:36 AM.
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Old 4th March 2010, 11:43 AM   #46
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Quote:
Originally Posted by Eva View Post
Do you think that this post is offtopic?
http://www.diyaudio.com/forums/solid...ml#post2105213
Essentially I'm telling that even a pair of back to back diodes and a single electrolytic capacitor are very effective to make toroids quiet, and I'm demonstrating it with waveforms captured from oscilloscope.
No, I don't think this regarded your posts - in the attachement I summarize it a bit.

I'm trying as I can replicate in my simulation program (Circuitmaker) different conditions from the mains (parasitics like unwanted dc components through rectifiers for half power mode). If I have success, then I can investigate exactly all mains DC filter topologies.

Who knows about modelling of toroidal transformers, especially the behaviour variations of different materials of the core? I want an equivalent circuit network of resistors, capacitors and inductors therefore.
Attached Files
File Type: pdf DC Filter effect.pdf (31.1 KB, 460 views)

Last edited by tiefbassuebertr; 4th March 2010 at 11:49 AM.
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Old 12th March 2010, 02:06 PM   #47
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this I have found today:
DIYCable.com : Intro Home Power Products
a combination of DC filter and such for RF/RFI
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Old 1st October 2010, 02:37 AM   #48
Ulisez is offline Ulisez  Mexico
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Quote:
Originally Posted by Jan Dupont View Post
Example one should do the trick (there are several threads about that particular DC blocker here). No need for lots of components. Just a nice simple way to prevent DC
Hi hope you can help me I've checked out the example one
how can I know the values I should use ?
or could you tell me wich to use please?
the ac where I live is 120-127

Thanks.
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Old 1st October 2010, 03:16 AM   #49
Ulisez is offline Ulisez  Mexico
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Quote:
Originally Posted by Ulisez View Post
Hi hope you can help me I've checked out the example one
how can I know the values I should use ?
or could you tell me wich to use please?
the ac where I live is 120-127

Thanks.
Sorry for the double post heres the examples.
Attached Files
File Type: pdf Main DC Filter 10 variations.pdf (56.3 KB, 305 views)
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Old 2nd October 2010, 12:04 PM   #50
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Quote:
Originally Posted by Ulisez View Post
Hi hope you can help me I've checked out the example one
how can I know the values I should use ?
or could you tell me wich to use please?
the ac where I live is 120-127
Thanks.
Hard to say. Also by my own circuit idea about post #33 for a bit more reliability.

If I know more about the exactly variations range of the DC components in your available main wall connection.

If you have a possibility, check your mains curvature at different times (morning-evening both working and weekend days) especially at that times, where your transformer produce a high level of buzzing/hum noise.
Very interesting to see would be various pics.

In this case also this URLs are of interest:
http://sound.westhost.com/cgi-bin/se...%2Fxfmr-dc.htm
dc filter

Last edited by tiefbassuebertr; 2nd October 2010 at 12:12 PM.
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