Switching frequency and bad sample transformers
Hi,
I just received 3 sample transformers from PI. They were built from the PI software outputs. Two of them are wired to the wrong pins. One of the three is wired to the correct pins. I am very disappointed with the quality control for sample transformers. It is clear by just looking at them that they are wired differently (see picture), but the test sheet says they are all the same. I put the one that was wired correctly into my circuit and it does not appear to work properly in the circuit, so I doubt if it is even right. Here is what I am seeing. The LNK623 that is driving the transformer is driving it at almost 300KHz instead of the specified 100KHz. What would cause this to happen? Would a bad/wrong transformer cause this? Also it does not look like the ratio of the primary waveform voltage to the sensing waveform voltage is correct - but that might be because it is at such a high frequency - not sure. Also, it should be noted that the output voltages on the DC side of things are much lower than the voltages that the PI software said I would get.
Please let me know how to proceed. This is a gating item for our product development.
THanks,
Tim
Comments
Hi,
I think the transformer I have in there may be correct. They are sending me new ones for the ones that were wired wrong, but this one appears to at least be wired correctly. However, the circuit still does not power up properly. The chip is generating 6V on the BP pin, but it is not switching as I would expect and the output voltages are very low. I have checked the circuitry attached to the supply ouputs and the current draw is well below the rated supply current. It seems like the supply tries to start and then quits. I have attached the waveform that I am seeing at the feedback pin. I have also included a zoomed in picture that shows the higher frequency stuff as well. Please advise how I should proceed. Thanks.
Tim
I got a new batch of sample transformers today. Looks like the wound these right because they work. Sorry for the run around. Amazing what a difference getting the right part makes.
Funny how that works...get the wrong parts and things don't work. Get the right parts...voila!
I wasn't involved in the original order but on behalf of Power Integrations I would like to extend my apologies for any delays this might have caused you and I certainly hope that it doesn't change your opinion about us or our products. If you need any help with the design you're working on, please don't hesitate to ask. Just reply back into this forum thread and I should get an email that it has been updated with a new comment.
Regards,
-The Traveler
It's incredibly unlikely that a LNK623 device is switching at 300kHz (unless you've accidently put a DPASwitch device in there instead). It's more likely an issue with the transformer....maybe some kind of resonance.
For the transformers, I can't directly help you over the this forum. If you call and speak to the person in charge of transformer samples I beleive this issue will get addressed quickly.
-The Traveler