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

[getfast_kiran]

Hi,
I have tried to build a smps with 5V, 0.8 A output to operate at universal voltage. From the design file generated by PI Expert 9.1.The device will power up and and function to give 5 V at the output at "ZERO" loading (No load condition).

But the moment I connect a Electronic Load the voltage will start to sink from 4.6V(Voltage when loaded - at near 0.1A) to around 3.9V(at full load of 0.8A). But still the circuit was able to handle the full loadcurrent for quite sometime and also I was able to still make it work at 0.9A above the design limit without IC shutting down.

What could be the possible reason of the voltage dip when loaded.

Thanks,
Kiran

[Inflex]

From where are you measuring the output voltage?

Do you have a scope to confirm that the output is at least reasonably stable, not a case of the decoupling cap not doing its part and leaving large valleys?

If the output is steady, I'd look on either side of the output inductor to ensure it's not dropping  voltage across it for what ever reason;  if it's full of valleys (high ripple) then blame the cap perhaps?

[tautech]

Inductors.
Why are you using L1 and L2 as series elements and not as a single common mode choke before the bridge ?

Is L3 capable of passing the current ? Have you checked for the voltage sag before L3 ?

[tatus1969]

try replacing your regulation zener diode by a proper TL431, The poor V/I characteristics of a regular zener diode will also result in poor load regulation.

[wraper]

    I have nothing against Indians. But for some reason, I often see new members from India trying to make some dangerous crap, while having no much clue about what they are doing. Wondering why this is so country specific. EDIT: besides those nearby traces between primary and secondary, TNY284 don't have a pin 3 for a good reason. Don't use standard footprint, there must be no pad on the pcb.

[mariush]

Agree with the two separate inductors L1 and L2.
Are you sure the zener diode is the right value (3.9v) ?

Other than this... don't have much experience with such circuits, but I can say the actual printed circuit board looks awful.
Here's some feedback..
Do you actually need to use 1n4006 diodes for the bridge rectifier? Save some space by using something like a KBP202G or KBP204G (through hole, SIP), for example : http://uk.farnell.com/multicomp/kbp202g/bridge-rectifier-200v-2a-kbp/dp/1861413  or DF* or DF*M if you want a DIP package , like this DF04M for example: http://uk.farnell.com/multicomp/df04m/diode-bridge-rectifier-1phase/dp/2306125
Use the extra space to maybe use bigger input capacitors (maybe lay them flat if you have some height restrictions) .. use same capacity for both so that you could get better prices in volume maybe.. for example use two 10uF 420-450v capacitors instead of a 6.8uF and a 4.7uF
No need to intersect traces on both sides of the board (see R4 and R3 on your design, you could make the traces go all on just one side of the board)
In fact the hole board could be made just one sided, for cheaper production costs, in worst scenario you just have to use a couple of jumper links (0 ohm resistors) in strategic places to jump over some traces.
For example, use a jumper link or 0 ohm resistor to jump across the 2nd trace going into the transformer, so that you won't break the safety area under the transformer with that trace going to C4.
You could also turn the chip around by 90 or 180 degrees and move the optocoupler UNDER the C4  (move the transformer up a bit) and then those two traces won't go over the traces going to transformer)  and you'll have an easier one side only circuit board
If you move the optocoupler under the C4 capacitor, you could also increase the safety of your thing by making a small cut from the edge of the board through the centers of the C4 and the optocoupler to increase the separation (by adding an air gap)
I'd use a bigger C7, maybe a 330-470uF ... basically at 10v rating, the difference in cost for capacitors are very small.
I don't think you need that precise resistors for R2 and R1 ... certainly not 2.05 megaohm 1% ... if it's cheaper, you can probably go for exactly 2 megaohm 1%, or maybe 4 x 1 megaohm resistors in series. Plenty of 2 megaohm resistors available, standard value, for example the MRS25 series from Vishay.

[wraper]

You have completely no current limiting through the optocoupler. Put some resistor in series at least. Also just a zener in series may not work so well.

[Inflex]

You could always work from their reference design to start with -

   https://ac-dc.power.com/design-support/reference-designs/design-examples/rdr-399/
   https://ac-dc.power.com/sites/default/files/PDFFiles/rdr399.pdf?download=1

[Zero999]

Hi,
I have tried to build a smps with 5V, 0.8 A output to operate at universal voltage. From the design file generated by PI Expert 9.1.The device will power up and and function to give 5 V at the output at "ZERO" loading (No load condition).

But the moment I connect a Electronic Load the voltage will start to sink from 4.6V(Voltage when loaded - at near 0.1A) to around 3.9V(at full load of 0.8A). But still the circuit was able to handle the full loadcurrent for quite sometime and also I was able to still make it work at 0.9A above the design limit without IC shutting down.

What could be the possible reason of the voltage dip when loaded.

Thanks,
Kiran

Does the output need be isolated from the mains?

If so, then there's no where near enough space between the primary and secondary traces on the board, so the output should be treated with the same precautions as mains voltage!

[Richard Head]

And the datasheet indicates a 1N4007 used in the primary snubber!

[wraper]

And the datasheet indicates a 1N4007 used in the primary snubber!

I only see UF4006 in the datasheet. There is a big difference between 1N400x and UF400x.
EDIT, I think you mean reference design for TNY288 on the link by Inflex, not a datasheet. Yep, that's strange, should be a typo.

[wraper]

BTW it is strange to use all through hole and just 3 SMD parts. It makes no sense to mix two technologies in such a way. I would understand if there was a lot of both, but just for 3 parts  .

[getfast_kiran]

From where are you measuring the output voltage?

Do you have a scope to confirm that the output is at least reasonably stable, not a case of the decoupling cap not doing its part and leaving large valleys?

If the output is steady, I'd look on either side of the output inductor to ensure it's not dropping  voltage across it for what ever reason;  if it's full of valleys (high ripple) then blame the cap perhaps?

Thanks a lot for the information. And Yes. I will try to measure the things you have said in the scope and get back to you on the same.

[getfast_kiran]

Inductors.
Why are you using L1 and L2 as series elements and not as a single common mode choke before the bridge ?

Is L3 capable of passing the current ? Have you checked for the voltage sag before L3 ?

Part 1 :

I was designing based on the software they provide for the Tinyswitch manufactured by ac-dc. I tried not to change much with the configurations since I wanted to test if it to just work.

Part 2 :

L3 was kept as specified by the software to the spec. I will try to check if there is voltage sag before L3. And I will get back to you.

thanks  so much for your help.

[getfast_kiran]

try replacing your regulation zener diode by a proper TL431, The poor V/I characteristics of a regular zener diode will also result in poor load regulation.

Definitely will try that. That is something I did not think till now. stupid me.

[Efig]

And the datasheet indicates a 1N4007 used in the primary snubber!

I only see UF4006 in the datasheet. There is a big difference between 1N400x and UF400x.
EDIT, I think you mean reference design for TNY288 on the link by Inflex, not a datasheet. Yep, that's strange, should be a typo.

No it is not typo. They use 1N4007GP which is glass passivated version with reverse recovery time 1-2us, which helps to reduce EMI.
Check documents provided by Inflex.

[getfast_kiran]

    I have nothing against Indians. But for some reason, I often see new members from India trying to make some dangerous crap, while having no much clue about what they are doing. Wondering why this is so country specific.

EDIT: besides those nearby traces between primary and secondary, TNY284 don't have a pin 3 for a good reason. Don't use standard footprint, there must be no pad on the pcb.

First Part :

Hi, I do not know if its general but in my case. I was  taught only theory at college. Never had the opportunity or exposure to hardware till I passed out.  Even though I tried so much to get my hands on it. I only got to see it after I passed out (without knowing much hardware... I know.!! ) even though I badly wanted to know about it. But things to make it and measure it etc was beyond my financial reach. So  once I had the opportunity to look at some hardware works after few years... I was truly intrigued. It was fun watching those hardware working like they would in theory and the additional hardship in practical circuits compared to in theory. So with help of peers and good people like you in various forums and guys like Dave who runs this blog, I  continue to learn it step by step in small sizes. hopefully I could be better like you guys with years to come. thanks for giving your insights on my doubts.

Second Part :
Could you tell me what is the clearance expected between the primary and secondary tracks. And I will edit the pcb without the trace as you told. But could you tell me what could be possible effect of not having that pad there.

[getfast_kiran]

Part 1:
Agree with the two separate inductors L1 and L2.

Part 2:
Are you sure the zener diode is the right value (3.9v) ?

Part 3:
Other than this... don't have much experience with such circuits, but I can say the actual printed circuit board looks awful.
Here's some feedback..

Part 3) a )
Do you actually need to use 1n4006 diodes for the bridge rectifier? Save some space by using something like a KBP202G or KBP204G (through hole, SIP), for example : http://uk.farnell.com/multicomp/kbp202g/bridge-rectifier-200v-2a-kbp/dp/1861413  or DF* or DF*M if you want a DIP package , like this DF04M for example: http://uk.farnell.com/multicomp/df04m/diode-bridge-rectifier-1phase/dp/2306125


Part 3) b )
Use the extra space to maybe use bigger input capacitors (maybe lay them flat if you have some height restrictions) .. use same capacity for both so that you could get better prices in volume maybe.. for example use two 10uF 420-450v capacitors instead of a 6.8uF and a 4.7uF

Part 3) c)
No need to intersect traces on both sides of the board (see R4 and R3 on your design, you could make the traces go all on just one side of the board)
In fact the hole board could be made just one sided, for cheaper production costs, in worst scenario you just have to use a couple of jumper links (0 ohm resistors) in strategic places to jump over some traces.
For example, use a jumper link or 0 ohm resistor to jump across the 2nd trace going into the transformer, so that you won't break the safety area under the transformer with that trace going to C4.
You could also turn the chip around by 90 or 180 degrees and move the optocoupler UNDER the C4  (move the transformer up a bit) and then those two traces won't go over the traces going to transformer)  and you'll have an easier one side only circuit board
If you move the optocoupler under the C4 capacitor, you could also increase the safety of your thing by making a small cut from the edge of the board through the centers of the C4 and the optocoupler to increase the separation (by adding an air gap)

Part 4:
I'd use a bigger C7, maybe a 330-470uF ... basically at 10v rating, the difference in cost for capacitors are very small.

Part 5:
I don't think you need that precise resistors for R2 and R1 ... certainly not 2.05 megaohm 1% ... if it's cheaper, you can probably go for exactly 2 megaohm 1%, or maybe 4 x 1 megaohm resistors in series. Plenty of 2 megaohm resistors available, standard value, for example the MRS25 series from Vishay.

Part 1: Okay.

Part 2: Yes it was Zener 3.9V, Following was the one I purchased.
http://www.digikey.com/product-detail/en/nxp-usa-inc/BZX79-B3V9,133/568-7936-1-ND/2762626

Part 3: Thanks so much for the indepth review.
a) Okay I will look at that diodes.
b) Really good suggestion and got to know how a experienced designer would think.
c) I will try to make that air gap and also de rearrangement. I actually placed the component by the suggestion of layout by the software in which they showed the optocoupler
on top of the transformer and the capacitor underneath it. So I went with it since I did not know much about the safety part of it.

Could you suggest how to make it more safer if you could or point me to any suggestion in this forum else for 230v 50Hz circuit.

Part 4:
Yes will test with that capacitor value.  Could you tell me why you specifically chose those values.

Part 5:
Okay will try it with the 2megaohm resistors.

Thanks a lot for such insightful help.

[getfast_kiran]

You have completely no current limiting through the optocoupler. Put some resistor in series at least. Also just a zener in series may not work so well.

Okay could suggest me a resistor value to be in series. Cause that zener value was important to get the reference value for regulation at the chip. So if I put a resistor there the drop could cause to shift the
regulation voltage reference by some value.
So do you think it would be healthy to add a resistor ?

[getfast_kiran]

You could always work from their reference design to start with -

   https://ac-dc.power.com/design-support/reference-designs/design-examples/rdr-399/
   https://ac-dc.power.com/sites/default/files/PDFFiles/rdr399.pdf?download=1

Okay I will try to design as per the one you gave. I tried to do it based on the layout suggested by the software.
So I forgot to take a look at the reference design. Do you think the layout was the reason behind the voltage
dip when loading or bad regulation.

[getfast_kiran]

BTW it is strange to use all through hole and just 3 SMD parts. It makes no sense to mix two technologies in such a way. I would understand if there was a lot of both, but just for 3 parts  .

I was trying to do it with the parts already available. Is that a bad practice in electronics scenario. Are there any bad aspects to it. would love your inputs on the same.

[getfast_kiran]

And the datasheet indicates a 1N4007 used in the primary snubber!

I only see UF4006 in the datasheet. There is a big difference between 1N400x and UF400x.
EDIT, I think you mean reference design for TNY288 on the link by Inflex, not a datasheet. Yep, that's strange, should be a typo.

No it is not typo. They use 1N4007GP which is glass passivated version with reverse recovery time 1-2us, which helps to reduce EMI.
Check documents provided by Inflex.

Thanks for clarifying the same and info.

[getfast_kiran]

You could always work from their reference design to start with -

   https://ac-dc.power.com/design-support/reference-designs/design-examples/rdr-399/
   https://ac-dc.power.com/sites/default/files/PDFFiles/rdr399.pdf?download=1

This was the layout suggestion the software gave. I know I made a it so huge compared to it. I was trying to make it more safer. I must have but instead made it worse. Could you suggest how could I make it safer. And also will it be the reason the voltage sinked so much.

[wraper]

Second Part :
Could you tell me what is the clearance expected between the primary and secondary tracks. And I will edit the pcb without the trace as you told. But could you tell me what could be possible effect of not having that pad there.

As much clearance as optocpoupler pins allow. If the device is not grounded (double insulated), I would aim for about 8mm, not less than 6mm, and then put a slot under the part (optocoupler, Y cap) which requires me to make lower distance.
No pad there won't make any effect. But if there is a pad, you may have an electric arc over it and small bang if, say, humidity is high.

[wraper]

This was the layout suggestion the software gave. I know I made a it so huge compared to it. I was trying to make it more safer. I must have but instead made it worse. Could you suggest how could I make it safer. And also will it be the reason the voltage sinked so much.

Don't forget that it is a layout on a single layer. But you managed to make much dirtier layout even on two layers while it should be completely opposite.

[mariush]

See this for clearance and creepage information : http://blog.optimumdesign.com/clearance-and-creepage-rules-for-pcb-assembly

Also this: http://www.smpspowersupply.com/ipc2221pcbclearance.html

In your board, the easiest way to increase the clearance is to not put traces under the optocoupler and the capacitor, anything you put between the terminals of those components reduces the clearance distance.
The distance between the pins of the optocoupler (if it's a DIP stile package) should be enough for this application (in my opinion). If you go further and create a slot between the pins, it's even better.

Something else i forgot to mention .. it's probably not needed since your product is low current (only 5v 0.8a) but for higher currents some designers also like to drill a series of small holes (like the holes for a regular chip pins or slightly larger) on the center line where the transformer would be placed (at equal distance between the terminals of the transformer).  Those holes would allow for a bit of air movement around the transformer potentially cooling it a bit. I don't think it's needed in your design.

Oh and some answers to your reply to my post...
For bridge rectifiers ... I'm not saying it's better to use bridge rectifiers instead of individual diodes, i'm just saying it looks nicer and takes less space on pcb and separates AC voltages from DC voltages much easier. Unless you go for the cheapest possible BOM (bill of materials) it's worth thinking about it.
Most cheap chinese designs use separate diodes because manual work is super cheap, they buy 100k pieces 1n4006 and some worker will be paid a dollar a day to shove diodes on the pcb. These days bridge rectifiers are not more expensive than 4 separate diodes if you buy them in some small volume (like let's say 50-100 bridge rectifiers, you buy them at less than $0.2 each)
If you want to build a lot of boards, replacing those diodes with a bridge rectifier may allow you to reduce the height of the pcb which in turn may allow you to put more boards on a single pcb panel and therefore you'd get more boards for your money.
Why 470uF for the second capacitor? 470uF is just a standard value and very common.. it's used in lots of products so chances are lots of stores will have it in stock in large quantities so at cheap prices. Also, it can probably be found at the same height and diameter as smaller capacitance capacitors like 330uF or 270uF and the price differences would be pennies if you buy a bunch of them. If you go over 470uF, you'll probably get taller capacitors and for 5v 0.8A, it won't make much of a difference.
Once you get the other problems sorted, it may be worth investigating if you could use 2 x 470uF or 2x560uF capacitors there, i mean use the same capacitor instead of the 1000uF capacitor, simply as a way to reduce the number of different components (and get better price by ordering a bigger quantity of same component) .. only if you plan on making more than a few of these boards.

[T3sl4co1l]

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

[wraper]

BTW it is strange to use all through hole and just 3 SMD parts. It makes no sense to mix two technologies in such a way. I would understand if there was a lot of both, but just for 3 parts  .

I was trying to do it with the parts already available. Is that a bad practice in electronics scenario. Are there any bad aspects to it. would love your inputs on the same.

You introduce 2 different manufacturing processes for no reason. It should be avoided, as increases production time and cost. Even if you see SMD components in production PSU, then usually they are put on the bottom of the PCB and glued with epoxy. So everything goes through wave soldering only once and reflow process is avoided.

[getfast_kiran]

Second Part :
Could you tell me what is the clearance expected between the primary and secondary tracks. And I will edit the pcb without the trace as you told. But could you tell me what could be possible effect of not having that pad there.

As much clearance as optocpoupler pins allow. If the device is not grounded (double insulated), I would aim for about 8mm, not less than 6mm, and then put a slot under the part (optocoupler, Y cap) which requires me to make lower distance.
No pad there won't make any effect. But if there is a pad, you may have an electric arc over it and small bang if, say, humidity is high.

Okay.

[getfast_kiran]

This was the layout suggestion the software gave. I know I made a it so huge compared to it. I was trying to make it more safer. I must have but instead made it worse. Could you suggest how could I make it safer. And also will it be the reason the voltage sinked so much.

Don't forget that it is a layout on a single layer. But you managed to make much dirtier layout even on two layers while it should be completely opposite.

Now you guys have reviewed it. It definitely feels dirtier. Will try to improve it as per suggestions.

[getfast_kiran]

BTW it is strange to use all through hole and just 3 SMD parts. It makes no sense to mix two technologies in such a way. I would understand if there was a lot of both, but just for 3 parts  .

I was trying to do it with the parts already available. Is that a bad practice in electronics scenario. Are there any bad aspects to it. would love your inputs on the same.

You introduce 2 different manufacturing processes for no reason. It should be avoided, as increases production time and cost. Even if you see SMD components in production PSU, then usually they are put on the bottom of the PCB and glued with epoxy. So everything goes through wave soldering only once and reflow process is avoided.

That was some good information. Now I understood why SMD parts are alone kept underneath. Did not think about it before. Thanks.

[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.

[getfast_kiran]

See this for clearance and creepage information : http://blog.optimumdesign.com/clearance-and-creepage-rules-for-pcb-assembly

Also this: http://www.smpspowersupply.com/ipc2221pcbclearance.html

In your board, the easiest way to increase the clearance is to not put traces under the optocoupler and the , anything you put between the terminals of those components reduces the clearance distance.
The distance between the pins of the optocoupler (if it's a DIP stile package) should be enough for this application (in my opinion). If you go further and create a slot between the pins, it's even better.

Something else i forgot to mention .. it's probably not needed since your product is low current (only 5v 0.8a) but for higher currents some ers also like to drill a series of small holes (like the holes for a regular chip pins or slightly larger) on the center line where the transformer would be placed (at equal distance between the terminals of the transformer).  Those holes would allow for a bit of air movement around the transformer potentially cooling it a bit. I don't think it's needed in your .

Oh and some answers to your reply to my post...
For bridge rectifiers ... I'm not saying it's better to use bridge rectifiers instead of individual diodes, i'm just saying it looks nicer and takes less space on pcb and separates AC voltages from DC voltages much easier. Unless you go for the cheapest possible BOM (bill of materials) it's worth thinking about it.
Most cheap chinese s use separate diodes because manual work is super cheap, they buy 100k pieces 1n4006 and some worker will be paid a dollar a day to shove diodes on the pcb. These days bridge rectifiers are not more expensive than 4 separate diodes if you buy them in some small volume (like let's say 50-100 bridge rectifiers, you buy them at less than $0.2 each)
If you want to build a lot of boards, replacing those diodes with a bridge rectifier may allow you to reduce the height of the pcb which in turn may allow you to put more boards on a single pcb panel and therefore you'd get more boards for your money.
Why 470uF for the second ? 470uF is just a standard value and very common.. it's used in lots of products so chances are lots of stores will have it in stock in large quantities so at cheap prices. Also, it can probably be found at the same height and diameter as smaller capacitance s like 330uF or 270uF and the price differences would be pennies if you buy a bunch of them. If you go over 470uF, you'll probably get taller s and for 5v 0.8A, it won't make much of a difference.
Once you get the other problems sorted, it may be worth investigating if you could use 2 x 470uF or 2x560uF s there, i mean use the same  instead of the 1000uF , simply as a way to reduce the number of different components (and get better price by ordering a bigger quantity of same component) .. only if you plan on making more than a few of these boards.

Thanks for the valuable information. I will try to take care of these aspects in the future..when I do design. Thanks a lot.

[T3sl4co1l]

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

[getfast_kiran]

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

This is the only option left to try. I will try to check that while I revise the board. Currently when I measure the voltage across the zener at full load was 3.7V. So do you think
it will result in the regulation problem ??

[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

Will surely try it and get back to you. It is very hard to get approval for making testing board. Hence Why I was waiting. I will try it now and get back to you. Thanks again.

[T3sl4co1l]

Test board?  Easy enough to air-wire on existing pads!

Tim

[tatus1969]

So I went with it since I did not know much about the safety part of it.

Could you suggest how to make it more safer if you could or point me to any suggestion in this forum else for 230v 50Hz circuit.

Is it a commercial product that you are developing? If yes, then please consider that you are developing a product that deals with lethal voltages and must be designed to protect the consumer in a professional, repeatable, certifiable and tested way. The regulation standards are the first place to go. They explain how to handle things like creepage, clearance, different levels of insulation (functional / basic / reinforced), which one to use when, and many more things.

Nevertheless, your questions and the level of your circuit design suggests that your design experience is (not yet) at expert level. Receiving feedback from a forum like this should not be your only source of learning. Developing mains powered devices requires a whole lot of experience, and I would not dare going this way myself without good backing from a good source of expertise, for example a senior expert within my company.

Just trying a shot in the dark: do you know the safety requirements for capacitor C4 in your design?

To the feedback circuit: a) it is most certainly the source of your bad load regulation. b) don't make the mistake to just replace the zener with a TL431, use the entire reference design from the TNY284 datasheet.

[getfast_kiran]

Test board?  Easy enough to air-wire on existing pads!

Tim

I was not having through hole component hence why. But since you told I am trying to do the air-wire thing to max possible on the existing pads. Thanks for sharing your views of an experienced person.

[getfast_kiran]

So I went with it since I did not know much about the safety part of it.

Could you suggest how to make it more safer if you could or point me to any suggestion in this  else for 230v 50Hz .

Part 1:
Is it a commercial product that you are developing? If yes, then please consider that you are developing a product that deals with lethal voltages and must be ed to protect the consumer in a professional, repeatable, certifiable and tested way. The regulation standards are the first place to go. They explain how to handle things like creepage, clearance, different levels of insulation (functional / basic / reinforced), which one to use when, and many more things.

Nevertheless, your questions and the level of your   suggests that your  experience is (not yet) at expert level. Receiving feedback from a  like this should not be your only source of learning. Developing mains powered devices requires a whole lot of experience, and I would not dare going this way myself without good backing from a good source of expertise, for example a senior expert within my company.

Part 2:
Just trying a shot in the dark: do you know the safety requirements for  C4 in your ?

Part 3:
To the feedback : a) it is most certainly the source of your bad load regulation. b) don't make the mistake to just replace the zener with a TL431, use the entire reference  from the TNY284 datasheet.

Part 1:
I was handed over this work when the experienced guy left suddenly. And he was the one who usually does this high voltage stuff. I presently hence do not have someone to ask to..about it.
This is for a prototype which after few iterations will be added to a board ( In long future). I am totally new to this high voltage circuit and as you told I told my boss I need someone with experience to assist me which I  was not allocated till now.
As you told apart from this forum am trying to read on it more. If you could suggest some good materials. That would be great.

Part 2:
I am not sure.  I am only learning. Is it that the capacitor has two different voltages on its both legs. So the clearance here is the distance between its legs. I have made a mistake by taking the trace go beyond the legs.
Is that the safety concern... Am I correct. If I am wrong Could you please tell me the correct safety requirements.

Part 3:
As you told and also as told by all others in the forum. I am trying to redesign a circuit as per the datasheet I was shared here.

 Thanks for you time. Please do advice me on the queries above. Thanks.
 

[mariush]

C4 must be Y-class capacitor (they're usually blue).

See this : http://www.kemet.com/Lists/FileStore/900%20Series%20Product%20Training%20Module.pdf  and this http://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do

Y capacitors are constructed in such a way that they're supposed to never fail in short circuit. If they fail, they're open, safe for the end user.

Other ceramic or electrolytic capacitors could fail short and then a major point for using transformer (isolation) would be lost.

[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?

[mariush]

I'd also be concerned about the transformer itself.
These ac-dc switcher chips require custom transformers and usually the datasheets are pretty low on the details about the number of windings, the wire thickness, the ferrite core type and so on. Do you guys know what you're doing when it comes to manufacturing the transformers, or are you ordering them from somewhere?

I've seen the datasheets for TNY** chips, I've also seen the datasheets for ST's Viper series and they're also not very detailed - Viper22 looks like a nice IC especially when paired with ST's TSM101 chip (voltage reference + voltage/current monitor, does the feedback for the chip through an optocoupler)... but again, it's still low on the technical details. Would be hard to use by a beginner.

One of the most detailed datasheets I know of is for the TEA172* chip from NXP ... : TEA1721 (max 5w) , TEA1723 (max 11w)

Lots of detail, lots of formulas to determine the components, it's a cheap IC which also uses a primary auxiliary winding to determine the output on the secondary side so it doesn't need a voltage reference and an optical isolator... you're saving money by not using those, but you may be spending a bit more money on the transformer..  the transformer would have to be custom made as it has the auxiliary winding between the primary and the secondary winding, and the secondary winding MUST have triple insulated wire to be absolutely safe for users.

As there's no feedback from secondary side, they may be less accurate with the output voltage but if the cost of manufacturing the transformer is the same as with other chips, you could just set the output voltage a bit higher than desired and spend 0.1-0.2$ (less than the voltage reference and optocoupler costs) on a tiny 5v linear regulator that would drop the 5.x volts to exactly 5v..

They also have an application note which explains their demo board and has lots of useful information for someone like you. Here's the application note : http://www.nxp.com/documents/user_manual/UM10521.pdf
And another one : AN11060  TEA172X 5 W to 11 W Power Supply/USB charger : http://www.farnell.com/datasheets/1760795.pdf?_ga=1.189448363.1081003429.1454881204

later edit: and they also have an online calculator sort of thing for these chips : http://nxp.transim.com/fb/design.aspx#General_InputSpecifications

Unless you guys have some investment in using those TNY chips, it may be worth looking at alternatives before committing to using them.

[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 design, input capacitor design, 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 design.

[getfast_kiran]

Hi,

Thanks for all your suggestion.

I have redrawn the board based as per your suggestions. Can you all please look at it and help me improve it.

[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

[getfast_kiran]

C4 must be Y-class capacitor (they're usually blue).

See this : http://www.kemet.com/Lists/FileStore/900%20Series%20Product%20Training%20Module.pdf  and this http://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do

Y capacitors are constructed in such a way that they're supposed to never fail in short circuit. If they fail, they're open, safe for the end user.

Other ceramic or electrolytic capacitors could fail short and then a major point for using transformer (isolation) would be lost.

That was a new knowledge to me. Plus I heard they are good at reducing common mode noise by coming across the transformer even though there is a contact between
the primary and secondary...Do you know if its that effective...

[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..

[getfast_kiran]

I'd also be concerned about the transformer itself.
These ac-dc switcher chips require custom transformers and usually the datasheets are pretty low on the details about the number of windings, the wire thickness, the ferrite core type and so on. Do you guys know what you're doing when it comes to manufacturing the transformers, or are you ordering them from somewhere?

I've seen the datasheets for TNY** chips, I've also seen the datasheets for ST's Viper series and they're also not very detailed - Viper22 looks like a nice IC especially when paired with ST's TSM101 chip (voltage reference + voltage/current monitor, does the feedback for the chip through an optocoupler)... but again, it's still low on the technical details. Would be hard to use by a beginner.

One of the most detailed datasheets I know of is for the TEA172* chip from NXP ... : TEA1721 (max 5w) , TEA1723 (max 11w)

Lots of detail, lots of formulas to determine the components, it's a cheap IC which also uses a primary auxiliary winding to determine the output on the secondary side so it doesn't need a voltage reference and an optical isolator... you're saving money by not using those, but you may be spending a bit more money on the transformer..  the transformer would have to be custom made as it has the auxiliary winding between the primary and the secondary winding, and the secondary winding MUST have triple insulated wire to be absolutely safe for users.

As there's no feedback from secondary side, they may be less accurate with the output voltage but if the cost of manufacturing the transformer is the same as with other chips, you could just set the output voltage a bit higher than desired and spend 0.1-0.2$ (less than the voltage reference and optocoupler costs) on a tiny 5v linear regulator that would drop the 5.x volts to exactly 5v..

They also have an application note which explains their demo board and has lots of useful information for someone like you. Here's the application note : http://www.nxp.com/documents/user_manual/UM10521.pdf
And another one : AN11060  TEA172X 5 W to 11 W /USB charger : http://www.farnell.com/datasheets/1760795.pdf?_ga=1.189448363.1081003429.1454881204

later edit: and they also have an online calculator sort of thing for these chips : http://nxp.transim.com/fb/.aspx#General_InputSpecifications

Unless you guys have some investment in using those TNY chips, it may be worth looking at alternatives before committing to using them.

Hi actually the guy who was doing ordered a bucket full of TNY284 chips almost a 1000 of them. So basically my boss want me to stick to it.

As you told I am worried if the transformer is problem cause now it started glitching even though I changed the feedback back to a TL431 based circuit with
1 transformer and out put goes from 4.8 - 5 v to suddenly 8v or 9v...
With another transformer....The glitch will be gone when I use another transformer but here the problem is the output will be at 12-11V...

do you know what might be the problem...behind it.

[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.

[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.