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'[EE]: Supressing fast transients'
2004\06\22@070013 by Ian Rozowsky

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Hi all

I'm currently putting an inverter design through compliance testing, and
have a problem with fast transients on the incoming power lines. I've added
common mode chokes and Y-cap to address conducted emissions, but electrical
fast transients are getting through, and dirupting operation of the
processor (16F870). I'm looking as some series inductors as a solution, and
was wondering if anyone on the list has had similar experiences, and how
they were resolved. Input currents are around 5A.

Regards

Ian Rozowsky
R&D Director
Centurion Systems (Pty) Ltd.
Box 506 Cramerview 2060 South Africa
roz**@centsys.co.za
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2004\06\22@085219 by Spehro Pefhany

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At 12:43 PM 6/22/2004 +0200, you wrote:
>Hi all
>
>I'm currently putting an inverter design through compliance testing, and
>have a problem with fast transients on the incoming power lines. I've added
>common mode chokes and Y-cap to address conducted emissions, but electrical
>fast transients are getting through, and dirupting operation of the
>processor (16F870). I'm looking as some series inductors as a solution, and
>was wondering if anyone on the list has had similar experiences, and how
>they were resolved. Input currents are around 5A.
>
>Regards

The CM choke should be taking care of the power supply issues, but maybe
there is other stuff getting through the inputs/outputs. You need to pay
special attention to the paths of those currents..

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\06\22@223914 by Richard Graziano

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Transient suppressors sometimes work, but not always.  Transients are often
quite problematic.  If you have a spectrum analyzer available you can
characterize the transient so that you will have some empirical starting
point.  Saturable core isolation transformers sometimes work as a
generalized solution but not always.  The problem is usually resolved by
determining the cause and the character of the transient.  For example, if a
large compressor is on the line a huge transient current of several hundred
amps will spike.  Varistors across the compressor motor will be the best
approach.

As far as the uP itself is concerned, you might want to steer clear of
inductive circuits that could be affected by large current transient because
of the reactive properties.  Fast schotkey diodes on the Vcc supply, right
at the processor chip like a free-wheeling diode can help.  The problem with
most diode solutions is that the diode selected is often slower than the
transient and ineffective.  There are fast schotky devices that will do the
trick.  Another important consideration that is sometimes overlooked is the
impedance of the power source that supplies the processor.  It should be as
low as possible with low ESR capacitors.  The higher the impedance the more
susceptible to transient noise.

If all of this has already been discussed, I apologize.  I have only seen
this for the first time.  If you would like to discuss your particular
circuitry off list, let me know.

I hope I have shed at least some light on your problem.
Regards



{Original Message removed}

2004\06\23@015959 by Ian Rozowsky

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Thanks to Sphero, Richard and Roy for their input!

The fast transients are being generated by a CE testset at the testhouse,
and superimposed onto the AC powerlines which supply the product. Every
300mS, the testset superimposes a 15ms burst of high frequency, high voltage
pulses onto the powerlines.

I want to try and kill off the transient right at the input, ie: before the
transformer which supplies all the low voltage electronics. Suppressing at
the processor is an option, but I'd prefer to stop the transient before that
point.

I'll report back as I go along!


Ian Rozowsky
R&D Director
Centurion Systems (Pty) Ltd.
Box 506 Cramerview 2060 South Africa
roz**@centsys.co.za
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{Original Message removed}

2004\06\23@092338 by ISO-8859-1?Q?Ruben_J=F6nsson?=

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> Thanks to Sphero, Richard and Roy for their input!
>
> The fast transients are being generated by a CE testset at the testhouse,
> and superimposed onto the AC powerlines which supply the product. Every
> 300mS, the testset superimposes a 15ms burst of high frequency, high voltage
> pulses onto the powerlines.
>
> I want to try and kill off the transient right at the input, ie: before the
> transformer which supplies all the low voltage electronics. Suppressing at
> the processor is an option, but I'd prefer to stop the transient before that
> point.
>
> I'll report back as I go along!
>
>
The transient generator generates a voltage with the groundplane as a reference. The current going in through the powerline wants to go back to the test generator, through the groundplane. There is a capacitive coupling between the groundplane and the PCB inside your device. You have to make sure that the electronics on your PCB isn't disturbed by the currents from the transient. This could be done in several ways:

Increase the impedance for the transients coming in through the powerlines. Use common and differential mode chokes for this.

Decrease impedance to the ground plane. If you have a metal housing (or a metal plane inside a plastic housing), connect Y capacitors between the power lines and the metal housing. The current then goes to the groundplane via the Y capacitors, the housing and the capacitive coupling to the groundplane instead of through your PCB. The impedance for the transients can be decreased even more by using a shielded cable for the power inlet. The shield should be connected to the metal housing via an EMC cable gland.

Make the PCB insensitive to the transients running through it. When the transient current is running through the PCB it creates voltage differences depending on the impedances in it's way. If this impedance is low enough, the voltage differences will not disturb your electronic circuits. This is done with more or less solid ground planes and decoupling. The power inlet should then be decoupled to this ground plane in order to let the current run directly through the groundplane instead of through the electronics before it hits the ground plane.

A combination of the above will have the best effect.

The transient currents are like any other currents, it will follow the path with the least resistance back to it's source, through whatever is in it's way.

Regards / Ruben
==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
.....rubenKILLspamspam@spam@pp.sbbs.se
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2004\06\23@100328 by David VanHorn

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At 12:43 PM 6/22/2004 +0200, Ian Rozowsky wrote:

>Hi all
>
>I'm currently putting an inverter design through compliance testing, and
>have a problem with fast transients on the incoming power lines. I've added common mode chokes and Y-cap to address conducted emissions, but electrical fast transients are getting through, and dirupting operation of the processor (16F870). I'm looking as some series inductors as a solution, and was wondering if anyone on the list has had similar experiences, and how they were resolved. Input currents are around 5A.


Sounds like you need another Y cap on the input side of the common mode chokes.

Handling current is like this: Make it hard to go where you don't want it. Make it easy to go where you do want it.  Current must always return to the source, so either you give it a nice path, or it will find an ugly path.

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2004\06\23@145615 by llile

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>The transient currents are like any other currents, it will follow the path with the least resistance back to it's source, through whatever is in it's

way.

<rant = on>
"FOllow the path with least resistance" is one of my pet peeves.  Current (or pressurized water in pipes, or air in HVAC ducts, or water draining down gutters, or anything else that flows) follows all available parallel paths (see Kirchoff's voltage law).  More of it flows where there is less resistance.  However, most people who quote this adage assume that *ALL* of the available current ( or water, or liquid sludge, or chocolate syrup)
flows on the path of least resistance and *NONE* flows along any other path.  Especially if they are not trained in the sciences (and even some who are).  If the paths are more than an order of magnitude different in resistance, then this is approximately true for practical purposes, but if
the paths are, say, 10% different this is very much not true. </rant>

Sorry this has very little to do with the topic of the thread.

-- Lawrence Lile





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06/23/2004 08:24 AM
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       cc:         Subject:        Re: [EE]: Supressing fast transients


{Quote hidden}

The transient generator generates a voltage with the groundplane as a reference. The current going in through the powerline wants to go back to the test generator, through the groundplane. There is a capacitive coupling between the groundplane and the PCB inside your device. You have to make sure that the electronics on your PCB isn't disturbed by the currents from

the transient. This could be done in several ways:

Increase the impedance for the transients coming in through the powerlines. Use common and differential mode chokes for this.

Decrease impedance to the ground plane. If you have a metal housing (or a metal plane inside a plastic housing), connect Y capacitors between the power lines and the metal housing. The current then goes to the groundplane via the Y capacitors, the housing and the capacitive coupling to the groundplane instead of through your PCB. The impedance for the transients can be decreased even more by using a shielded cable for the power inlet. The shield should be connected to the metal housing via an EMC cable gland.

Make the PCB insensitive to the transients running through it. When the transient current is running through the PCB it creates voltage differences depending on the impedances in it's way. If this impedance is low enough, the voltage differences will not disturb your electronic circuits. This is

done with more or less solid ground planes and decoupling. The power inlet

should then be decoupled to this ground plane in order to let the current run directly through the groundplane instead of through the electronics before it hits the ground plane.

A combination of the above will have the best effect.

The transient currents are like any other currents, it will follow the path with the least resistance back to it's source, through whatever is in it's

way.

Regards / Ruben
==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
KILLspamrubenKILLspamspampp.sbbs.se
==============================

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2004\06\23@150311 by David VanHorn

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>
>Sorry this has very little to do with the topic of the thread.
>
>-- Lawrence Lile

Not at all, it's an important distinction.
What you create is a mesh of impedances. More of the current will follow the lowest impedance path.

If you do your layout sloppily, then you end up with a pretty much random distribution, which results in symptoms like "when I plug in the sheilded cable, the noise gets WORSE!". Very frustrating and confusing until you see what's happening, then it's a screaming clue to the problem.

Layout done right is like a proper sewer system, nearly all the S*** goes where you want it to, almost all the time.  (Feel free to quote this.. :)

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2004\06\26@074620 by Howard Winter

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On Wed, 23 Jun 2004 14:03:04 -0500, David VanHorn wrote:

> Layout done right is like a proper sewer system, nearly all the S*** goes where you want it to, almost all
the time.  (Feel free to quote this.. :)

Sir Joseph Bazalgette would have been proud!  He built the London sewage system, about 150 years ago.  Let's
see how the analogy runs...

He built Interceptor Sewers (Y capacitors?) that collected the effluent and ran gently downhill in enclosed
tunnels to keep going the right way (shielding, chokes?), merging together and getting bigger until they
reached the sea (supply Earth).  There were one-way self-closing doors at junctions that stopped an
unexpectedly high level in one part of the system from flowing back up another (diodes?).  To cope with storms
there were weirs that allowed excess effluent to flow over into a secondary system (varistors?).

That seems to work reasonably well!  :-)  Gives me a way to remember how to do it in future...

The one problem he had that doesn't map is that the downhill flow ended below sealevel, so he had to build a
pumping station to bring it back up - I'm not sure if this situation has an analogue in electronics?

Cheers,

Howard Winter
St.Albans, England

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2004\06\26@091451 by Jake Anderson

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charge pump?

though it was shorted to ground ;-P


{Quote hidden}

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2004\06\26@101750 by David VanHorn

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>
>The one problem he had that doesn't map is that the downhill flow ended below sealevel, so he had to build a
>pumping station to bring it back up - I'm not sure if this situation has an analogue in electronics?

Sure. The pump is the battery.
In our world, everything happens above ground.

Now there is that strange land that has a negative battery, and apparently everything is helium-filled. :)

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2004\06\28@002825 by jayhanson

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>From: pic microcontroller discussion list [EraseMEPICLISTspamMITVMA.MIT.EDU]
On Behalf Of Ruben Jönsson
>
>Increase the impedance for the transients coming in through the powerlines.

>Use common and differential mode chokes for this.

I am new to this type of noise problem (so please don't laugh).

I am experiencing a noise problem in an automotive application.  I
understand the y-cap, ground plane, etc. that has been discussed in the
thread so far.

My question is how is the microhenry value of the inductor calculated?  I am
experiencing a burst of noise of about 100 mhz on the 12v dc side of the
battery.  What value of choke would be optimized to cancel this noise?

Tnx,
Jay

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2004\06\28@042757 by Bob Axtell

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I design a lot of stuff for police vehicles, so maybe I can help:

jayhanson wrote:
>>From: pic microcontroller discussion list [RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU]
>
> On Behalf Of Ruben Jönsson
>
>>Increase the impedance for the transients coming in through the powerlines.
>
>
>>Use common and differential mode chokes for this.
>
>
> I am new to this type of noise problem (so please don't laugh).
>
> I am experiencing a noise problem in an automotive application.  I
> understand the y-cap, ground plane, etc. that has been discussed in the
> thread so far.
>
> My question is how is the microhenry value of the inductor calculated?  I am
> experiencing a burst of noise of about 100 mhz on the 12v dc side of the
> battery.  What value of choke would be optimized to cancel this noise?

First, make SURE that it is coming into your circuit through the 12V battery line. While it IS possible of course, my experience is that it gets in through other means. Anything conductive that goes from your application to anywhere else is suspect. Every wire that enters your application (except the antenna, if it has one) MUST have an RF choke and a cap; that's the bad news. The good news is that MOST of those supressors can be 0805 components, with a value of 50pH or so. But you have to have the cap, too, about 47pF is plenty.

If your gadget isn't in a metal case, you will probably have continuing
problems. Automobiles are notoriously noisy electrically, and except for fairly mundane electronics, everything that has semiconductors needs to
be shielded.

Next, I'd focus on making sure your application is properly grounded. The heaviest wire has to be the ground wire, and it has to be as close to the battery negative lead as possible. This CAN'T be stressed to much.

Finally, noise coming in from a mushy battery charging system (sounds like what you are seeing there) is usually fixable by designing a switching regulator front-end. Passive regulators are NOT very good at stopping electrical noise, but switchers do an amazing job, and NO noise will get through it. We have found that using a step-down switcher instead of a passive regulator is actually CHEAPER, because the heavy chokes on the 12V line are bulky and more expensive than the switcher (go figure..).

Good luck! And let us know what ya find out!

--Bob



>
> Tnx,
> Jay
>
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2004\06\28@152132 by jayhanson

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>Bob:
>
>Finally, noise coming in from a mushy battery charging system (sounds
>like what you are seeing there) is usually fixable by designing a
>switching regulator front-end. Passive regulators are NOT very good at

Thanks Bob, I will follow your advice.  The automotive environment is
unbelievably hostile.  One can't believe the scope traces...

Are you using TI simple switchers for your switching power supplies?

Jay

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2004\06\28@162521 by David VanHorn

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At 08:40 AM 6/28/2004 -1000, jayhanson wrote:

>>Bob:
>>
>>Finally, noise coming in from a mushy battery charging system (sounds
>>like what you are seeing there) is usually fixable by designing a
>>switching regulator front-end. Passive regulators are NOT very good at
>
>Thanks Bob, I will follow your advice.  The automotive environment is
>unbelievably hostile.  One can't believe the scope traces...

Seen an alternator load dump pulse yet?  SAE talks about +/- 400V IIRC, with some amps behind it.

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2004\06\28@165509 by Bob Axtell

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jayhanson wrote:

>>Bob:
>>
>>Finally, noise coming in from a mushy battery charging system (sounds
>>like what you are seeing there) is usually fixable by designing a
>>switching regulator front-end. Passive regulators are NOT very good at
>
>
> Thanks Bob, I will follow your advice.  The automotive environment is
> unbelievably hostile.  One can't believe the scope traces...
>
> Are you using TI simple switchers for your switching power supplies?

Yes. Aren't they awesome? Beats virgin birth, I think...<g>.

--Bob


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> Jay
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2004\06\29@043245 by jayhanson

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>From: pic microcontroller discussion list [EraseMEPICLISTspamEraseMEMITVMA.MIT.EDU]
On Behalf Of Bob Axtell
>
> Are you using TI simple switchers for your switching power supplies?
>
>Yes. Aren't they awesome? Beats virgin birth, I think...<g>.

The simple switchers really are easy to use.  One last question, did you
consider optioisolators (where they would work)?

Jay

==============================

>From: pic microcontroller discussion list [@spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU]
On Behalf Of David VanHorn
>
>Seen an alternator load dump pulse yet?  SAE talks about +/- 400V IIRC,
with some amps behind it.

I put ZNR 2000A varisters
http://rocky.digikey.com/WebLib/Panasonic/Web%20data/ERZ-V,D%20Series.pdf on
the alternator, starter, and the ignition, but I am still getting +/- 80V
noise on the 12V supply line.  It's the power supply from hell!
Unbelievable!

Jay

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2004\06\29@045357 by Bob Axtell

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jayhanson wrote:

>>From: pic microcontroller discussion list [.....PICLISTspam_OUTspamMITVMA.MIT.EDU]
>
> On Behalf Of Bob Axtell
>
>>Are you using TI simple switchers for your switching power supplies?
>>
>>Yes. Aren't they awesome? Beats virgin birth, I think...<g>.
>
>
> The simple switchers really are easy to use.  One last question, did you
> consider optioisolators (where they would work)?

Yes, they work well. I use NEC's PS2505 optos when isolating inputs such
as brake pedal signal, strobe lights, spotlight etc. I like these
AC-input types because they allow the installer to wire it forwards or
backwards and the signal gets into the computer correctly.

Again, since you are carrying these signals into your PCB, you must use
RF chokes and caps on each input.

--Bob

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2004\06\29@075708 by Alan B. Pearce

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>The one problem he had that doesn't map is that the
>downhill flow ended below sealevel, so he had to build
>a pumping station to bring it back up - I'm not sure
>if this situation has an analogue in electronics?

Charge Pump ?? :))))
Boot Strap Capacitor ?? :))))

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2004\06\29@151048 by jayhanson

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>From: pic microcontroller discussion list [spamBeGonePICLIST@spam@spamspam_OUTMITVMA.MIT.EDU]
On Behalf Of Bob Axtell
>
>Again, since you are carrying these signals into your PCB, you must use RF
chokes and caps on each input.

Thanks a million Bob. You should write a book on the subject.

C U Later,
Jay

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'[EE]: Supressing fast transients'
2004\07\01@152128 by Andrew Warren
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David VanHorn <PICLISTEraseMEspammitvma.mit.edu> wrote:

> > The automotive environment is unbelievably hostile.  One can't
> > believe the scope traces...
>
> Seen an alternator load dump pulse yet?  SAE talks about +/- 400V
> IIRC, with some amps behind it.

   For a good overview of the automotive environment, along with
   advice on dealing with it, see Tom Williamson's Intel Appnote
   AP-125, "Designing Microcontroller Systems for Electrically Noisy
   Environments":

       http://www.intel.com/design/mcs96/applnots/21031302.pdf

   -Andy

=== Andrew Warren -- RemoveMEaiwEraseMEspamspam_OUTcypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2004\07\01@161154 by Bob Barr

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On Thu, 1 Jul 2004 12:23:37 -0700, Andrew Warren wrote:

>
>    For a good overview of the automotive environment, along with
>    advice on dealing with it, see Tom Williamson's Intel Appnote
>    AP-125, "Designing Microcontroller Systems for Electrically Noisy
>    Environments":
>
>        http://www.intel.com/design/mcs96/applnots/21031302.pdf
>

Excellent reference, Andy. Thanks for posting it.


Regards, Bob

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