SMPS - TNY 284 - 4W design - Regulation distorted by Loading.

[getfast_kiran]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

Okay..Incase you get the translation. Please do share.
I have attached the  diagram with this...and also the PCB  for the same.Only difference that I have made are
1. R3 is 20 ohm instead of 18 ohm

[getfast_kiran]

Does anyone think the use of following (SB140)
http://www.vishay.com/docs/88715/sb120.pdf

instead of the IN5819 Diode
http://www.diodes.com/_files/datasheets/ds23001.pdf

could result in the regulation problem and drop in the output voltage.

Basically the same thing.

I already gave the solution,

Zener diodes under 6V do not have a sharp (avalanche) characteristic.  They are true zener diodes: a very soft knee.  The rated voltage is only true under the test current; expect wildly different results for other conditions.

Use a TL(V)431 instead.

Tim

Hi,

Re-did the circuit with TL431 as you told. But now the problem is the circuit is working with output of 4.8-5V at no loading but suddenly like a glitch the voltage raises to 8-9V...repeatedly. What could be the possible problem.

[getfast_kiran]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

I have attached the PCB and circuit diagram can you please take a look and tell what might be the problem behind the glitch in output voltage.

[T3sl4co1l]

C8 should have a resistor in series. Adjust values for good compensation.

Tim

[tatus1969]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your circuit drawing, that allows us to better help you.

it is this one: http://www.eurobuch.com/buch/isbn/9783772376825.html

[tatus1969]

A bad situation that you are in. I would go for 1:1 copying an existing reference design in your situation. For further reading, I suggest to go for the safety regulation standards. Google "psu safety regulations" gave me this article as a good starting point: http://www.de.cui.com/catalog/resource/power-supply-safety-standards-agencies-and-marks.pdf Purchase the relevant safety standards, and read them carefully.

Re C4: mariush gave the answer that I was hoping for  Remember, your design effort can affect the safety of other people. I hope, this example shows it clearly. If you design C4 to be something else than an Y capacitor, people can be put into lethal danger. You *must* know what you are doing, otherwise... I don't know... maybe it would be better to talk to your boss and explain him your situation?

Yes thanks for giving reference to that safety standard. I remember them having huge cost. Does every company purchases such document for standardization or is available anywhere in the internet for the download.

As you told I understand there is great problem with safety of the problem..I am trying to make a documents with the books and papers you guys suggested to make him understand
its dangerous for a newbie like me...(Although I am worried he may fire me). So till that he allows I am really hopinh you guys would help me with the same.

Thanks again..

use google, youll find their online stores. depends on the standard, typically a few 100 usd

[tatus1969]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

I have attached the PCB and circuit diagram can you please take a look and tell what might be the problem behind the glitch in output voltage.

i'd turn on my scope and have a closer look. plus carefully read the tny284 datasheet once again, the two control pins are both multi purpose. how does the switch node voltage look like.

[getfast_kiran]

C8 should have a  in series. Adjust values for good compensation.

Tim

Hi, I added the resistor to it. But even now the glitch is present. Hence I tried to see if its problem with the transformer or the input side. So I replaced the transformer and checked it with two other.

So I checked the input and it showed glitch.

The pic of the glitch in input between the Drain(switch node) and source(power ground) is attached.
What could be the reason for it.

[getfast_kiran]

A bad situation that you are in. I would go for 1:1 copying an existing reference design in your situation. For further reading, I suggest to go for the safety regulation standards. Google "psu safety regulations" gave me this article as a good starting point: http://www.de.cui.com/catalog/resource/power-supply-safety-standards-agencies-and-marks.pdf Purchase the relevant safety standards, and read them carefully.

Re C4: mariush gave the answer that I was hoping for  Remember, your design effort can affect the safety of other people. I hope, this example shows it clearly. If you design C4 to be something else than an Y capacitor, people can be put into lethal danger. You *must* know what you are doing, otherwise... I don't know... maybe it would be better to talk to your boss and explain him your situation?

Yes thanks for giving reference to that safety standard. I remember them having huge cost. Does every company purchases such document for standardization or is available anywhere in the internet for the download.

As you told I understand there is great problem with safety of the problem..I am trying to make a documents with the books and papers you guys suggested to make him understand
its dangerous for a newbie like me...(Although I am worried he may fire me). So till that he allows I am really hopinh you guys would help me with the same.

Thanks again..

use google, youll find their online stores. depends on the standard, typically a few 100 usd

Yes I will search with the reference as you told. Thanks.

[getfast_kiran]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

I have attached the PCB and circuit diagram can you please take a look and tell what might be the problem behind the glitch in output voltage.

i'd turn on my scope and have a closer look. plus carefully read the tny284 datasheet once again, the two control pins are both multi purpose. how does the switch node voltage look like.

Hi I had tried to look at the switch node voltage as you told. And following is the waveform that is coming from the switch node during the glitch period...it almost cyclic in nature.

I have attached the wave form during the glitch...at the switch node..ie; from drain(one going to the inductor) to the source of the TNY284. could you please take a look and see the
problem here.

[getfast_kiran]

On noting the voltage across the Bypass pin.  I am getting voltage of -170V ...and around. for a smd that is rated for 10uf.

The capacitor 10uf has only 16V. Trying to find how that voltage appears acroos the 10uf, 16v capacitor at bypass pin.

[tatus1969]

C8 should have a  in series. Adjust values for good compensation.

Tim

Hi, I added the resistor to it. But even now the glitch is present. Hence I tried to see if its problem with the transformer or the input side. So I replaced the transformer and checked it with two other.

So I checked the input and it showed glitch.

The pic of the glitch in input between the Drain(switch node) and source(power ground) is attached.
What could be the reason for it.

that is not a picture of the output voltage showing the glitch. do you have one?

[tatus1969]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

I have attached the PCB and circuit diagram can you please take a look and tell what might be the problem behind the glitch in output voltage.

i'd turn on my scope and have a closer look. plus carefully read the tny284 datasheet once again, the two control pins are both multi purpose. how does the switch node voltage look like.

Hi I had tried to look at the switch node voltage as you told. And following is the waveform that is coming from the switch node during the glitch period...it almost cyclic in nature.

I have attached the wave form during the glitch...at the switch node..ie; from drain(one going to the inductor) to the source of the TNY284. could you please take a look and see the
problem here.

The switch voltage looks as it should. You see it going GND (control chip conducting), then going HIGH (transferring energy to the output), then showing self oscillation of transformer. The cycles look regular, nothing suspicious to me. But if you have a glitch, you should probably zoom out further, and use a second channel to simultaneously capture the output voltage.

But you seem to have a measurement problem, that oscillation in the region of 1MHz should not be there. It is not coming from the circuit. Where did you connect the ground clip of your oscilloscope to? It should be connected to pin S of the TNY284. You need to use an isolation transformer to run your PSU to make this measurement (you need it for your safety anway).

[getfast_kiran]

C8 should have a  in series. Adjust values for good compensation.

Tim

Hi, I added the resistor to it. But even now the glitch is present. Hence I tried to see if its problem with the transformer or the input side. So I replaced the transformer and checked it with two other.

So I checked the input and it showed glitch.

The pic of the glitch in input between the Drain(switch node) and source(power ground) is attached.
What could be the reason for it.

that is not a picture of the output voltage showing the glitch. do you have one?

Yes you are right. That was not the waveform the usual wave across drain and source. IT was picture of sudden glitch happening in the input side of the circuit prior to transformer.

[getfast_kiran]

@mariush, you are right, there is a ton of things that need to be taken into account. i have a 500 page book on this topic. safety rules, winding construction, skin effect, leakage inductance, topologies, core types, different types of power losses, output filter , input  , emi filtering, and countless other topics.

normally you go to one of the transformer manufacturing specialists and let them wind your custom part. but for a number of specific chips they have stock parts that are matched to the corresponding reference .

Could you please tell the book that you were referencing.
And currently my new board is showing output of 4.85 - 5.00 but it will glitch to 8-9V for a second and comeback to 4.85 -5V regularly with one transformer.

And it will not glitch but generate a voltage of 12V at the output with another transformer of same rating.

do you think it is due to problem of transformer winding

i'm afraid but that one is in german, but i can check at home maybe there are translations. what is the winding ratio of your transformer? plus please post your  drawing, that allows us to better help you.

I have attached the PCB and circuit diagram can you please take a look and tell what might be the problem behind the glitch in output voltage.

i'd turn on my scope and have a closer look. plus carefully read the tny284 datasheet once again, the two control pins are both multi purpose. how does the switch node voltage look like.

Hi I had tried to look at the switch node voltage as you told. And following is the waveform that is coming from the switch node during the glitch period...it almost cyclic in nature.

I have attached the wave form during the glitch...at the switch node..ie; from drain(one going to the inductor) to the source of the TNY284. could you please take a look and see the
problem here.

The switch voltage looks as it should. You see it going GND (control chip conducting), then going HIGH (transferring energy to the output), then showing self oscillation of transformer. The cycles look regular, nothing suspicious to me. But if you have a glitch, you should probably zoom out further, and use a second channel to simultaneously capture the output voltage.

But you seem to have a measurement problem, that oscillation in the region of 1MHz should not be there. It is not coming from the circuit. Where did you connect the ground clip of your oscilloscope to? It should be connected to pin S of the TNY284. You need to use an isolation transformer to run your PSU to make this measurement (you need it for your safety anway).

Hi,

I used an 300Vrms input capable high voltage probe with an MSO to measure it. Is this right way to measure or should I have used any other technique.
There was isolation transformer available and have requested for it.

As you have told I am attaching the following wave forms
1) Voltage across drain and source during normal operation. I really do not know why its in the negative region. Is it because I used the scope wrong.

 Presently I attached the ground of the probe to the drain and the other lead to the source plane.
 
2)I have attached the output waveform of the same at the 5v dc output.
But interestingly what the scope is showing is an alternative wave with heavy 3rd harmonics.

or I must have made a stupid measurement mistake.

3) since I found an ac waveform at the output DC terminal when looked through scope. I  used the True RMS multi meter to measure the voltage at the
dc output of the SMPS

Avg : 2.4 V
Peak: 9.07 V
Min:0.01 V

[tatus1969]

1) does not look like mosfet vds. you say gnd=drain, probe tip=source?? why? thats wrong. you didn't use an isolation transformer when measuring on primary side? what scope model is it (some are isolated, most not and will die in that short circuit you are creating).

2) on the ourput, where was the gnd clip connected?

this all sounds very confused. are you sure you want to continue doing this? it really leaves the impression that you are close to killing yourself. do you really have substantial knowledge in power electronics to handle this? not meaning to be rude, just heavily concerned.

[T3sl4co1l]

Please use an isolation transformer, and connect the probe ground to the common of the circuit being probed.

Tim

[getfast_kiran]

I have asked for an isolation transformer as you have told.

I replaced the Tinyswitch from TNY284 to TNY266 and I got the output of SMPS with very good regulation.

Thanks for all you people help. I am learning as I go...with help of you all. I will comeback again to TNY284 to
test the same at current of 1A again as I get some freetime from current projects.

As of now TNY266 is providing required regulation as per requirements. All you guys suggestions helped me attain the same.
Thanks each and everyone of you for your valuable help.