TOP227Y
Hello PI people - We have had a number of failures of the TOP227Y in a design we inherited from another company. The design was taken right from the TOP227 data sheet with what appear to be minor modifications. I have been able to obtain failed boards and have replaced just the TOP227 and they work just fine. The TOP227s had blown off their plastic lids. During testing, I noticed that we have a very large di/dt through the transformer. I have attached some waveforms and a schematic of the pertinent components around the TOP227. In the the two 4 channel pictures channel 1 is the "control" voltage on pin 1 of the TOP227. Channel 2 is the drain to source voltage of the TOP227. Channel three is the tranformer primary current and channel 4 is the filtered output 15VDC. Both of these pictures are the worst case startup waveforms that I found. The two channel picture is of the worst case di/dt in the transformer with the Vds of the TOP227 at 100nS scale. I have measured the transformer leakage and magnetizing inductances (they are rigidly controlled) of the tranformer primary at 17uH and 997uH respectively. Please review these and comment.
Dennis Laugen
Design Engineer
Advanced Energy Ind.
Comments
Hello Dennis,
TOPSwitch has built-in current limiting. Worst case scenario the maximum Drain current will be 3.3A (http://www.powerint.com/sites/default/files/product-docs/top221-227.pdf, page 11). Even with repetitive over current events the part is protected because of the second safety mechanism, the latching thermal shut-down. This explains why we believe your problem is not current related.
If there is any part physically destroyed, you have to check the maximum voltage applied to Drain terminal. TOP227Y could be destroyed if the Drain voltage goes over 700V. I do not have any data about your DC rail voltage, but counting the 200V zenner voltage you have to make absolutely sure the PFC stage in front of your power does not have over voltage spikes around 500V.
The second way to destroy TOP227Y is with the clamp diode D6 (or D7, the voltage limiting zenner). If together with TOPSwitch you have D6 (or D7) failures you have to double check the whole clamp circuit.
Cheers,
PI_Crusher
Thanks Crusher
i am very suspicious of overvoltages also and am looking into transients on the DC feed. I may just try to overvoltage one to see where it breaks. The guys who designed it probably should have gone to a higher voltage part. Under nominal 208V single phase AC in, the peak Vds of the TOP227 is about 620V due to about 110V peak of ringing, if the ringing I'm measuring is all real. Not much margin.Any suggestions for bringing the ringing down? I'll let you know what I find.
Hi Dennis,
For really high input voltages you can go for a dramatic approach as described in StackFET paper: http://www.powerint.com/community/papers-circuit-ideas-puzzlers/circuit-ideas/-high-voltage-input-switching-power-supply-usi
If the front PFC is not going over the board with really big over shoots, there are two other options you can try before moving for the StackFET overkill:
1) Adjust the transformer leakage for a lower value in order to decrease the magnitude of the leakage energy
2) Redesign the transformer using our PI Expert free software because you can quickly tune the VOR parameter (the amplitude of the reflected output voltage) for decreasing the peak Drain voltage. This could give you the extra margin you need.
Cheers,
PI_Crusher
... or replace D7 clamp zenner with 150V
Good morning, I need an electrical schematic for a 30V 1.2A source using the TOP227YN and EF25 core. Can someone help me?
Hi alex eletronica,
Thank you for your interest of using Power Integrations' part.
Regarding your request, I need more detailed specification for your requirement but for your convenience we have PIExpert tools that would provide you all Power Supply design needs. Just need to register and then just input your application and specification and you will be provided with schematic, BOM, transformer design and layout recommendation. This tools will help you on all your future Power Supply design needs. See link below. Thank you.
https://ac-dc.power.com/design-support/pi-expert/pi-expert-online/
I was able to do it OK here.