TOP271 design not providing full output current
Low output current capabilty at 110V
Hello, We are testing a TOP271 implementation that is designed to provide 48VDC @ 2.5A max over the universal input voltage range. The problem we are experiencing is that at 110V input we are only able to draw up to 900mA before the supply starts to reset itself constantly and we need to remove the load for the output voltage to return to 48V. The output diode is a 3A type and does not get warm at all. If we increase the input voltage to 240V then the output current capability rises to 1.6A before resetting occurs [we believe this is thermal overload of the diode] but this does not explain the much lower output current capability at 110V input. We are using a similar circuit to that in design example DER-97 ie. with the 30V zener in the feedback circuit to reduce the TL431 supply voltage to 18V, see attached circuit....
We need to resolve these issues as quickly as possible as the product is due for release very soon.
Looking forward to your reply.
David
Comments
Hello, Please find attached the schematic as a PDF and the transformer construction...
I believe the device is loosing regulation before dropping out as the output voltage drops out and then the device trys to auto-restart.
David
David,
Did you use PIExpert for this design? If yes, could you please send me the design file please?
Hi Konobi,
Attached is the original design used for SMPS. The only changes we have made are to the feedback network as we have incorporated the 30V zener and adjusted the feedback gain resistor to 3K3 and some other values inline with the DER-97 application note.
I did raise another thread about the 3V3 output voltage not be stable when there is no load on the 48V output but I think we are going to do away with the 3.3V output and sub-regulate down to 3V3 from the 48V supply.
David
David,
1. Could you please power up the supply using a high voltage DC source (120VDC) instead of AC and try to load the power supply and then check if the problem persists?
2. Can you please confirm the device is actually in auto restart? (Look at the c-pin waveform; in case of auto-restart, a triangular waveform between 4.8-5.8V is observed on this pin)
3. I know you mentioned that none of the power devices/switches heat up before the supply loses regulation. Could you please confirm this one last time please? Is the secondary diode, clamp components, MOSFET heating up?
4. Lastly, load the supply at low-line(**AC input**) to a point where it is just about to shut down yet still in regulation (900mA as you mentioned) and observe the bulk capacitor voltage waveform. Look at the valley(minimum value) of the rectified AC sine wave and confirm that this value is higher than 87VDC.
david plz check your topswitch temperature.....you need to ensure its exact contact with the heatsink.if top switch entire surface is not touching properly with heatsink then too it will go down in shutdown and again resart after few seconds.
regards
vaib
David,
If none of the components heat up before the power supply shuts down then its unlikely a thermal issue. It is more likely that the device is hitting its maximum duty cycle limit (given the fact that the device can be loaded more at high line) and then enters auto restart. Could you please confirm that the device enters auto-restart after losing regulation?
Also, would you mind sharing the schematic (I cant seem to zoom into the schematic attached) and transformer construction data please.
Cheers!