TOP260EN 100W ref design

Hi ncc1701jr,

Thank you for using Power Integrations' part.

Sorry for quite late reply due to weekend.  Regarding your problem, removing the 8V/0.4A output from the circuit shout not caused the problem you are encountering with the fuse blowing or output irregularities. Can you give me some some info so I can better asses your problem.

Are you using our sample board from DER-218 or you designed your own board?  If you design your own can you share your schematic and your PIExpert spreadsheet?

Control pin is a multifunction so you should properly bias this.  This is providing supply so it should be between 4.8V to 5.8V to avoid auto restart.  It is also the feedback pin from the output and compensation pin setting poles and zeros.

Y-caps should not caused operation problem.  As you can see on DER-218 RTN output is connected to EARTH then connected to NEUTRAL with Y-cap.  Bulk+ is also connected with Y-cap to RTN.  

Thank you and hopefully it helps.  Can you attached my requested schematic and spreadsheet file so I can assess better.

Hello Mallora

Thank you for your responce,

We have designed our own board, so the schematic is attached.

Our fuse problem has already been solved. It was caused by the isolation transformer we use to separate the psu from the mains.

Our first transformer was an EFD30 but this was too small as your spreadsheet suggests. Now an off-the-shelf transformer has been put in. This is the WE-760895431. As this one is not in your spreadsheet a datasheet is attached.

The bias voltage is applyed externaly because the transformer has a 18V bias winding. It has been set to 5,2V as your last post suggested. But the control pin goes directly to error mode (auto restart)

Hello Mallora,

Just a quick update. The new transformer has brought some good things but not all the way, as you can see in the scope image. When i apply the mains the transformer does nothing, then it starts kicking (so the output voltage goes up but the power transfer isnot continuous.). a few seconds later it goes into full operation for a few second. At which time the whole cycle starts again.

This cycle continues even when all protective circuits have been turned off. (V-pin to gnd, x-pin to gnd).

Setting the IC to 132kHz will only make it worse as it will repeat the cycle but never reach full operation.

Hope you can help,

NCC1701JR

Hi ncc1701jr,

Based on your transformer, you are completely using different design with what is used in DER-218 which is your reference.  Inductance and turns ration is completely different so I suggest just copy what is in DER-218 design.  You can also use the link  below to help you with your design.  All you need to do is input your specs and it will provide you the transformer design for your power supply.

https://piexpertonline.power.com/site/login

Thank you for your responce.

Unfortunatly none of the transformer bobbins suggested in PI Expert will fit in our enclosure. It can only accomodate 27 mm in height. Is there a function in PI Expert where i can specify a hieght requirement?

Can the transformer throw this circuit into chaos? There should not be a problem as long as the output voltage is the same as the reference design, right?

last question, have you seen such behaviour in a smps before?

Thank you in advance,

NCC1701JR

Hi ncc1701jr,

Transformer is a critical component of the power supply.  There are alot of considerations you need to meet based on your specifications like primary inductance, flux density, Output Reflected Voltage (VOR) in order to operate properly.  Picking out of the shelf transformer with just the output voltage consideration will not work most of the time as I said that you have alot of things to consider.