15W SPMS with TNY288
We have designed a power stage based on TNY288 for a new product.
The design is based upon PI expert results.
See the schematics.
Actually we are testing the prototypes and it doesn't work.
The TNY always fall on auto restart, except on two configurations:
- when C7 is removed, TNY work as expected, but the regulation is bad due to lack of filtering, as soon as we put a capacitor on C7(whatever the value), auto restart begin.
- whan power is switched off, TNY start working fine with regulation as expected, but for only a few seconds as C1 and C2 discharge. TNY start working when Vdrain goes down to 280Vdc.
Our transformer is made with a EF25 core instead of EEL19, but all the turns and dots are as specified by PI Expert.
What issue could we encounter ?
Thanks for your help.
Comments
Hi PI-Terry,
I did what yout told me, use EF25 for simulation with PI expert. It gave me results as 63turns for primary, 4 turns for secondary 1 and 8 turns for secondary 2.
When tested, the system works well from 85Vac to 150Vac (with its best at 110Vac), above it begins to auto restart.
The input selected for simulation was 195-265Vac.
What did I do wrong ?
| Attachment | Size |
|---|---|
| Alim_carte_CMF_v3.pdf (2.09 MB) | 2.09 MB |
Hi,
I have just made a new simulation, but this time using PIxls. And I get different results. What is the difference between the two softwares ?
Why did I need a trifilar winding for primary with PIxls and only a single one with PIexpert ?
Regards.
| Attachment | Size |
|---|---|
| Alim_CMF_V4.pdf (2.69 MB) | 2.69 MB |
Forgot my last post.
I spent some times on PIXLs and application notes relatives, so I can figure out a bit more.
Can someone confirm me that the primary winding wire diameter could be one of my problems.
After solving PIXLs warning, it happens that my actual wire is larger than required, parameter CMA is at 1062 for 27AWG. By setting the wire at 31AWG, it falls at 421.
Should it be an issue ?
If someone can give me a quick answer before I start again to rewind my samples, it should be very appreciated.
Regards
JY
Hi,
This is not a critical issue, if CMA is higher, it means the wire gauge is over selected. It is proposed to select smaller wire gauge if the CMA is out of the range. But it should not be the root cause of the critical issue.
Hi,
After focussing on the transformer, I found my issue. The Vrm of the second secondary ouput diode ( 20Vdc) was too low (40V) after selecting the proper one, the initial design work fine.
Regards.
Hi,
Looks like the power supply went into some fault conditions, which causes the auto restart to protect the power supply.
From what I understood from your description, you used the EF25 core, but follow the turns and dots that designed for EEL19, correct? This may create the problem, EF25 and EEL19 cores are very different. Actually, I would like to recommend you to modify the core from EEL19 to EF25 in your PI expert design, and then follow the transformer spec for EF25 core. If you still see this issue, you can attach you PI expert design, I can further help you.