LNK6667E voltage instability and oscillating

Posted by: Yasar Arafath on 02/05/2018

Hi,
I have already used LNK6428K , successfully completed the design and getting stable voltage of 5V,2A..Now i am working with lnk-hp 6667E and working for same 5V, 2A using same transformer i had for LNK6428K but i am getting instability voltage and its keep on oscillating. When i fine tuned the feedback resistors by the formula given in AN58 DESIGN sheet, also not getting constant voltage with no load. Please suggest me some ideas to get the constant output voltage for 5V. feed back resistor RB1 43.5K and RB2 10.85K, also i have attached transformer design..

Files

EE16_flyback.png (204.99 KB)

Comments

why i did not get response for my query, please do reply.

where is your schematic? engineers on this forum cannot read minds...

here with i attached the schematic followed and transformer design i used, Please clarify.

Attachment	Size
schematic (77.89 KB)	77.89 KB
transformer design (204.99 KB)	204.99 KB

Hi Yasar,

Thanks for your inquiry in our LNKHP solutions. Please clarify the following.
1) Are you using LNK6667E or LNK6766E?
2) What is your output voltage 5V or 12 and the load current?
3) Efficiency requirement.
4) Are you using a metal heatsink for the E package?

To better understand the problem can you send both actual schematics you are using for LNK6428K and LNK6766E\6667E? I would like to understand your modifications from your 1st working design LNK6428K to this new design LNK6766E\6667E?

Did you use the PIExpert or the PIXLS? Please send so I can check.

Regards,
PI-Picard

Dear Picard,

Good Day!!
Good Day !!

I am Using the LNK6428K its 5V, 2A design.
As per the design its not giving 5V output its giving only 4.4V but as per the application note and data sheet load regulation will be in the range of +/-5% i.e 0.25V.

I attached application note schematic and Tx design.

Attachment	Size
smps_1.PNG (63.17 KB)	63.17 KB
Transformer.PNG (406.57 KB)	406.57 KB

Hi eman.

Thank you for using PI product on your design. We would like to know the below information.

1. Do you have a cable or wire from the power supply output to the load? If yes, where did you measure the output voltage regulation? Is it on the load side or power supply output side?

2. Did you try decreasing the value of R6. Right now it is 27K in parallel with 20K. Try reducing the 27K to 20K or lower and check if the regulation is going near the 5V.

Thank you.

Best Regards,
PI-SevenofNine