Main current limit shifting in TFS764HG
My TFS764HG design is intended to operate with 100% main current limit. Nevertheless, some of the units shift to a lower current limit (typically, 80%) in continuous operation, sometimes after tens of hours of operation. The unit returns to normal operation after cycling the AC power. What could potentially be the cause of this? Is there any guideline to avoid this problem? Is there a way to disable the reduced current limit selector feature?
Comments
No, the front end is not PFS. The DC bus voltage is 355V. Six TFS 2-switch forward converter power trains are connected in a load sharing scheme. The TinySwitch flyback portion is not used. We see some of the 6 channels shift to a lower current limit for no apparent reason (actually, to 60%, rather than 80%, as I indicated previously). This happens sometimes after 48 hours of normal operation. The rest of the power trains compensate for the loss of current, while the faulty channel operates in the 60% current limit mode.
What condition at the pins could trigger false current limit detection? Is there a way to disable the 60%/80% current limit selection permanently?
Hi,
Could you please remove the faulty unit and test it on a bench seperately (with out using any load sharing technique) and let me know what happens.
Regards,
PI-NANO
Hi,
What exactly do you mean, whether the output voltage is coming down when you load with 100% load during continuous operation?
Could you please share the specifications and schematics of your design?
Could you please specify the operating conditions of your board such as input voltage, input current, output voltage, output current, ambient temperature and TFS device temperature. If you’re driving the TFS stage with a PFS stage, then please measure the DC bus voltage as well.
Regards,
PI-NANO