Plz suggest me for better Radiated Emission test results.

My transformer details are as per following
ETD-39
L p = 383 uH.
1)Primary = 31 T (2 x 26 S.W.G)
2)Secondary = 3 T (4 x 21 S.W.G)
3)Bias = 3 T ( 2 X 30 S.W.G)

Shield I have used 30 s.w.g 48 T

4 mm margin on both side of core;.

Suggest me a better architecture of transformer for radiated emission test results.
and it is ok to use flux band over core and connected it to bulk ground.

Hi Rajyavardhan,

I do not have all of the specifics for your transformer like turns, wires, cores, layers, strands etc.
If your question is related to Screen 2 then, increasing the number of strands is used for reducing the turns and total stack height when still keeping full layer for better shielding effect of that winding.
For your power level I would replace Wound Screen 2 with single turn of foil with a center connected lead along the turn.
You may have a better results when Removing Shield 1 and connecting the core to a quiet point via very short lead.
Best Regards,

Hi Rajyavardhan, thank you for sending the transformer information to me.
Please look at the attached picture and let me know if all of the stack and schematics information is correct.

Hello,

I am working smps based battery charger and I am using INN3379 pro.
I am facing out put current limiting problem its not content
example - I was set current resistor 6.65E for 4amp as per PI design but now when input ac voltage 120vac I can draw 1amp current and input 230vac than I can draw 2.5amp.

also I need constant power set points setting example code.

Hi SANDEEP ,

Thank you for the question.
I need to see the design before to make any suggestion. Please share a link to the design or send the whole file to piexpert@power.com

Best Regards,

Please find the attached design file.

Hi Sandeep,

Thank you for using PI product. We are willing to help you in your inquiry but if may I request, can you please create a new ticket for this one since this thread discusses a different topic?

We will wait for your new post.

Thank you and Regards,

PI-Lupin the Third

yes..

Ok, Rajyavardhan, Thank you!

1. I would recommend removing the first layer shield and attaching the core to HVDC buss line with very short lead.
2. replacing the wound shield W5 with a single turn of copper foil. The lead soldered to the center of the foil and pin 1(HVDC bus) to be also extremely short.
3. The same copper screen to placed between Bias WD4 and secondary WD3. Also connected to pin 1 or HVDC buss if different.
4. Use TIW for secondary and remove the safety margins
5. Reduce primary layers to one and single strand, but increase the diameter of it to fill the layer properly.
6. Use copper flux band as shown on the picture.

On the picture is also shown the suggested transformer.

Best Regards,

The cu Foil Option Is not Feasible at supplier end, due to Mass Production of Transformer.
So i updated Transformer Design sheet Instead of Using Litz i had gone for larger Diameter conductor on both Primary as well as secondary.
for proper result how should use flux band.

If you cannot use foil you should try to increase the strands of the shield winding in order to reduce its turns when covering the same window length.

Many turns shield winding never works well for 2 reasons.

1. The voltage on the end is too high, so the shielding effect is very small compared with the "cancellation" effect caused by the generated voltage on the one end of the wire. Ideal shield is equipotential.
2. The self inductance of multi turns winding is big, so it is not very effective in "soaking the noise"

Unfortunately your long window is requiring many turns to fill a layer, and the better way to overcome the problem is to increase the strands.

The implementation of the copper and wire flux bands are shown on the picture with the proposed foil transformer. I copy it again below

Best Regards,

Thanks for u r useful reply.
suggest me some tips for conducted emission test.

Hi Rajyavardhan

If your transformer as close as possible to the suggested one
- split primary or secondary
- small number of turns, big layer covering wound shields (if no copper screen available)
- core connection to a quiet point
- flyback swing point buried in the first layer
- flux band lead - short and tight,
- twisted together secondary
you should not have problem with the emissions from the transformer side.

If a problem with the emissions still exist, it probably relates to PCB loops, filters...

OK ,
i observed that (blanking timing) current spike at turn on of mosfet is increased in shielded transformer but less in without shield transformer is it due to parasitics capacitance and inductance in transformer?

is it ok to place shield winding at last of all windings and attached to bulk capacitor ?

if only used single shield winding.

Hi Rajyavardhan,

The noise energy is not in the flat part of the signals but is in the switching portion of the signal. The shield is used in the transformer to close the noise loop with short path to the source.
So, trying to limit the spread of the noise around the transients points inevitably is leading to increasing the parasitic capacitance to them. It means:
- better nose coupling and reducing the noise spreading
- unfortunately it also increases the switching losses and lower efficiency.
Y caps and filters are other possible approaches.
There is no a miracle (ultimate) solution for most of the problems in SMPS. And this is especially true for the flyback converters.
The workable solution always is in the tradeoffs and balances between the requirements and actual implementation.

Best Regards,

Thanks for u r great reply,
but if i put Shield winding after P2 is it causing any effect on radiated emissions,
because now my trx is already prepared & without shield is having better ID & VDS waveform .

On 70+W power level I very much doubt it that you can comply with EMI class B, earth connected load, without internal screens.
Screen on top of the second part of the primary would not make the difference from fail to pass at the above conditions.
Best Regards

Thanks for Your Reply,

There is audible noise in board how to remove it , with shield transformer is having higher noise at full loading conditions.

it is coming at higher input voltage 200v to 265v.

Hi Rajyavardhan
You need to look over the switching waveforms.
It may be OV or OVP.
https://ac-dc.power.com/sites/default/files/product-docs/topswitch-jx_family_datasheet.pdf
page 7

suggest me input filter Values for 72 W SMPS 12 V , 6 A.

I already passed Conducted emission by 9.11 dB.
Suggest me Trials for Radiated Emission other than internal cu foil on transformer .

Hi Rajyavardhan
Great news.
You can try Y capacitors.

i already used lots of y caps
plz let me know from where should i used another y cap..
i am attaching sch.

Hi Rajyavardhan,

You can try connecting class y capacitor between the two quiet points of the transformer. Primary to secondary.
Some of the capacitors on the circuit you are providing may not help though.

You should contact the local PI representative with the specification, schematics, PCB, EMI results for detailed help.

Best regards,

how to improve Radiated emission test Margin in SMPS TOP271 Based ,it is pass only by 0.78dB?
Further suggest how to analyse the results of radiated emission test?

Hi Rajyavardhan,

Very basically, you need to took at the waveforms and try to find ringing shapes with same or close frequencies as the amplitudes from the EMI graph. Than, damp them.
It also helps to insert and move a noise 'sniffer' probe around
- high dv/dt and di/dt pcb tracks,
- transformer and
- input & output lines.
- power switcher and rectifiers
- input and output filters.
Look at the noise probe signal when the oscilloscope is switched to FFT in a similar range of the noise amplitudes from the EMI measurement.
Any sharp edges in the waveforms are feeding the parasitic resonant tanks with energy and that ringing is what you see on the radiated emissions. Sharp edges must be smoothed with close by snubbers.
Those are generic advises and basic principles.
For particular "on board' implementation and detailed help please contact your PI local representative.

Thanks, For U r great Reply
Please suggest me Document or Method For perfect Tuning of RC snubber in output Rectifier diodein flyback converter.
I might Be thinking that Output snubber can fix my Problem.