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Bypass Capacitor Start-up Problem TNY278PN

Posted by: Bruno Marques Macedo on

Hi!

I have been using TNY278PN for years in a design but now I need to increase the current limit.

I changed bypass capacitor from 100nF to 10uF and it worked as expected: I could reach to a higher output power.

Problem: when turning on the power supply after desenergizing, sometimes TNY does not start-up. It seems the 10uF capacitor does not discharge, and when powering on, the state machine does not recognize the capacitor.

What can be done to fix it?

Comments

Submitted by PI-BERJ on 03/05/2021

Hi Bruno,
Can you provide more details on your design, e.g. input/output voltage/power, etc. A schematic is also helpful if possible, i.e if there are other circuits connected to the BPM e.g. a bias winding. Changing the current limit from reduced to increased, to accommodate more output power, would also require a corresponding change in the value of the flyback transformer primary winding inductance. Kindly verify in PIExpert if it is still within the recommended range of values.
How quick is the 're-energizing' cycle? Is this equivalent to an input chatter test?
Have you also verified that the 10uF capacitor is the issue, i.e. the capacitor fails to discharge fully during the re-energizing cycle?
Regards,

Submitted by Bruno Marques Macedo on 03/08/2021

Hi!

Thanks for your prompt reply. Here in attachment the SCH.

When changing to 10uF capacitor (increased current limit) I recalculated the design in PI Expert and it kept transformer primary inductance in the same range.

The issue is that the capacitor dos not discharge in some turns-off.

Attachment Size
pi-1600x12002x_scale-iflex.png 584.04 KB
Submitted by PI-BERJ on 03/08/2021

Hi Bruno,
Do you have any waveforms to show that the 10uF capacitor is the issue? Can you also upload the PIexpert xls/pdf output? Does the issue occur more at low line? I still suspect that we need to at least decrease the primary winding inductance.
Regards,

Submitted by ehsanhabib on 04/04/2021

I have a Design based upon LNK6766K. Output Required 24 Volt 1.5 amp. The problem is

1. Output voltage reaches up to 29 Volt while no Load is connected.

2. Even at just 200mA load SMPS goes into auto start Mode. It pulses every 1 Second.

Attachment Size
Pi expert Design file 8.83 KB
Submitted by PI-Lupin the Third on 04/07/2021

Hi ehsanhabib,

Please create a new post for your inquiry. If you this this forum post is related to your inquiry then you may simply copy the link instead. Looking forward in your post.

Thanks and regards,

PI-Lupin the Third