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Old 10th December 2004, 09:21 AM   #11
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Quote:
Originally posted by allanon77


Sorry but why do you think so? because I don't talk about every SMPS's rules ... ... thank you for your suggestion I will talk with my boss about my lacks ...
I'm a electronic designer, young, but however I designed some SMPS in the last years.

Anyway ... I thank you for everything you said. You gave many useful information for new designers....
etc
X Eva
Sorry for my irony!
after my post I read other your posts and I have to say that you effectly know much about SMPS (more than I ).
My question is: have you ever designed a SMPS for audio application? have you measured the noise ... oops ... ripple at high frequency, with what results?
Do you agree with my idea to make a SMPS in a different box with a shielded cable to supply the amplifiers?
And I read (other post) that you avoid paralleling of different capacitors because that causes ringing oscillation, but if I place between the capacitors a small resistor probably this could be a solution at the problem; secondly probably this kind of oscillation have a high frequency content (MHz) because I suppose they are generated by parasitic inductance and the capacitances so a further reduction of these oscillation could be the shielded cable (I talked before).
I thank you in advance.
Regards

Giuliano
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Old 10th December 2004, 10:52 AM   #12
AGGEMAM is offline AGGEMAM  Denmark
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jackinnj, I am talking about a clockless or self oscellating circuit so speaking of delay cycles is in principle not the case. However you do have a point but it entirely depends on the design. You have to have a feedback loop that is several times faster than the switching circuit for one. The real problem is the floating equivalent switching frequency in the MHz range which makes use of transformers pretty much useless.

allanon77, though long cables will decrease stray magnetic fields in the PS and the amp from influencing eachother. It also increases the radio transmitted ripple and if the cable is long enough, this might affect all your household appliances. Sure you can use shielded cable but no shielding is perfect.
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Old 10th December 2004, 11:55 AM   #13
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Default Are there SMPS forums?

X Eva or ... who wants

Do you know if there are other SMPS forums?
Thanks

Giuliano
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Old 12th December 2004, 10:40 AM   #14
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Hello, I have designed amplifier with SMPS two years ago (when I was sixteen years old).
Here jou can see some photos...
It (SMPS) delivers up to 1kW of power..
Now I am designing amplifier with linear power supply, because SMPS makes too much noise in supply and everywhere else.
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Old 12th December 2004, 11:55 AM   #15
AGGEMAM is offline AGGEMAM  Denmark
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Quote:
Originally posted by blasteriz
Now I am designing amplifier with linear power supply, because SMPS makes too much noise in supply and everywhere else.
I thought that Eva had made the point quite obvious that noise in SMPS's is something you can design your way out off. But it's not only in the schematic design but even more so in the PCB design. And the latter being a more trial and error part or sheer luck than anything else really.
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Old 12th December 2004, 11:58 AM   #16
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Yes, PCB and grounds means a lot..
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Old 12th December 2004, 07:31 PM   #17
Eva is offline Eva  Spain
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Noise is for those who have no interest in understanding what happens inside a SMPS [or for those that talk a lot about signals they have never seen on an oscilloscope]

'Noise' is not the right term for SMPS since it means a 'random not-deterministic signal' and SMPS allways output and radiate deterministic and periodic parasitistic signals

Those signals are the sum of a main ripple component [a sqare or triangle wave at the switching frequency] and some parasitistic ringing components [at a few Mhz] caused by RLC parasitistic resonances between windings, diodes, transistors and PCB tracks

Ripple by itself is easily filtered and happens at too low frequencies to be sustantially radiated

Ringing is harder to filter because it is easily radiated due to its higher frequency nature. Also, ringing versus efficiency is a compromise since ringing may be reduced or killed just by slowing down switching transients [more switching losses], increasing PCB and transformer DCR [to damp parasitistic RLC at the expense of more dissipation], using inherently slower high voltage switching devices like bipolar transistors or IGBTs [not prone to ringing as opposed to MOSFETs], etc...

You may build a working and reliable SMPS but, how much does it ring at switching transients?. Taming ringing requires a lot of trial and error
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Old 12th December 2004, 07:59 PM   #18
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want to reduce noise -- try some of the slew-controlled chips from Linear Technology --

the cheap fix is to use a linear post-regulator -- Linear has an application note combining the LT3439 switcher chip with the LT1761 and LT1964 ultra-low noise linear regulators.

i have some Sorensen telcom switching supplies which have "noise" in the uVs -- totally discrete (and they are ancient!)
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Old 13th December 2004, 06:55 AM   #19
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Quote:
Originally posted by Eva
Noise is for those who have no interest in understanding what happens inside a SMPS [or for those that talk a lot about signals they have never seen on an oscilloscope]

'Noise' is not the right term for SMPS since it means a 'random not-deterministic signal' and SMPS allways output and radiate deterministic and periodic parasitistic signals

Those signals are the sum of a main ripple component [a sqare or triangle wave at the switching frequency] and some parasitistic ringing components [at a few Mhz] caused by RLC parasitistic resonances between windings, diodes, transistors and PCB tracks
I agree with your assertions but probably "noise" is an uncorrect but simple way to understand what you are talking about: "unwanted signals". But it's true that if you talk about "noise" could be source of misunderstandings because you put toghether different kind of signals with different characteristics (and wirth different way to limit). However normally when I say "noise" I know what I am talking about.

Quote:

Ripple by itself is easily filtered and happens at too low frequencies to be sustantially radiated


Yes but probably for audio application it's the more important to limit ... isn't it true?

Quote:

Ringing is harder to filter because it is easily radiated due to its higher frequency nature. Also, ringing versus efficiency is a compromise since ringing may be reduced or killed just by slowing down switching transients [more switching losses], increasing PCB and transformer DCR [to damp parasitistic RLC at the expense of more dissipation], using inherently slower high voltage switching devices like bipolar transistors or IGBTs [not prone to ringing as opposed to MOSFETs], etc...

You may build a working and reliable SMPS but, how much does it ring at switching transients?. Taming ringing requires a lot of trial and error


But if you use BJT you don't have the possibility to use more than one component for a switch, this is not a big limitation (for dissipation, size, etc...).
In the past I studied a new design of a Boost PFC (1kW) and I choosed the power switch (frequency choosed 50kHz output voltage 400V, wide range application); At the end I had to choose between 2XIRFB20N50K e 2XIRGB20B60 so I estimated the power losses of the switches (I had some limitations: case not bigger than TO-220 and dissipator with Rth=1.7C/W).
The winner was: IRFB20N50K. What do you think about? Did I made some mistakes?
Thank a lot

Giuliano


X Jackinnj

Yes your solution to use at the end a linear regulator, like what you talked about, could work but probably not for audio amplifier with some watts (that is my case). Thanks.
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Old 13th December 2004, 12:51 PM   #20
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Quote:
Originally posted by allanon77

X Jackinnj

Yes your solution to use at the end a linear regulator, like what you talked about, could work but probably not for audio amplifier with some watts (that is my case). Thanks.
yes, the linear regulator burns watts. but DIYr's don't have to advertise the fact that their products are "green".

for the moment, Linear's site seems to be down, but I note that they do have a low noise gate driver, and that the 1A chip like the 3439 can be used to drive other devices. it is really worthwhile to take a look at the PDF or the Application Notes for these devices.

the LT3439 has come down in price -- $7 each -- pretty stemmy compared to a TL494 or SG3525 -- but you probably save in terms the magnetics and snubbers, if you want a low noise power supply.

one thing which both National and Linear take great effort to point out is that some of the current pathway's conduct a lot more than one would suspect (and for very brief periods of time) -- there are nanohenries everywhere!
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