auto-restart lnk625
I order you 1 month ago more or less some transformer and lnk625 integrates for building a flyback supply. I have tried to run the supply correctly but it has been impossible, it looks like the integrate go into auto-restart because the voltage in the feedback pin is not enough. I spent several days but I didn’t know how I could solve this. Integrate and transformer work properly standalone and I have followed the PI designer for choosing the components. Could you see something wrong in the design maybe?
I send you the schematic which we are working with. We want to get 16V, 0.125A and 3W
Any idea will be well received. Thanks for your time.
Comments
Yeah, the schematic is based in your document rdr201. There is a mistake in the typed i want to get 6W instead of 3W. The winding in the transformer is the same that PIXls designer 7 indicated: 115 in the primary, 21 in the secondary and 12 in the feedback (firstly it puts 20 but warning about EMI advised to me decrease the number until 12). The primary inductance is around 1.85mH at 100KHz and the maximum leakage inductance is aroun 74uH. It looks everything ok, but it doesn't work. I measured the feedback pin around 1.9V (it seems good for the trigger) and 6V in bypass (the treshold for reset is about 5.7V...so it seems good). I don't get the IC trigger, and sometime i was able to do triggering the IC but it doesn't work correctrly. Can you see something wrong in the windings or inductance?? Is there any thing which i can test??
Does the converter ever have a regulated output -- at light load? If converter never developes enough output voltage to regulate then either the phasing of one or more windings are wrong or the turns ratio is wrong. Do you see flyback phase as positve and forward phase as negative for sense and output windings?
The output is not regulated i am only have a charge of 100 ohms. And i can 't see anything beacuse most of the time the IC not trigger and when it do it i can't distinguish anything only like a noise each time. I have tested with several IC
Increase the value of C7 to about 470uF Low ESR type. You can reduce the value of C8 to about 150 uF
I ve changed C7 and C8 as you propouse me, but i don't obtain new results. I believe maybe the problems are in the IC, do you know something about??Because the design is the same that the program propouse me.
Schematic design looks correct. I suspect transformer windings sre being connected properly. Also check primary inductance.