PMP21549: No output voltage

Look at L1 or R4. One of them is the problem. The voltage at TP9 is not high enough to turn on the controller. This is just based on a quick glance of the schematic.

Hi, Andrew, thanks for your comment.  two follow-up questions:

1. I have used the schematic and BOM provided by TI to put this together, so what could be wrong with either L1 or R4?
2. What can I do to increase the voltage to turn on the controller?

Again, thank you.  I appreciate your reply!

What’s the voltage between L1 and R4 in reference to ground? Either could be faulty.

OK.  319 V on either pin of L1.  319 V on the leading pin of R4, then 1.8 V on the other.  So bung resistor?  Or just an incorrect value do you think?

Thank you!

Hi Mark,

Was your problem resolved?

thanks,

Brian

I swapped R4.  Still no voltage on the secondary side...  No idea now...  Any other ideas?

Hi Mark,

Something on the VIN node of U3 is keeping C13 from charging.  Check the polarity of C13 to make sure it was not installed backwards.  Also, with power off, measure the resistance between TP9 and TP3, to see if something may be shorted.

thanks,

Brian

I meant to say VIN node of U1; not U3.

Hi, Brian.

I've checked again.  The polarity of C13 is correct on my PCB.  The resistance between TP9 and TP3 is 3.6 Ohm.

Thoughts?

Looks like the LM5021 might be damaged.  Can you remove U1 and see if the resistance between TP9 and TP3 increases to much higher impedance?

OK, so I went and populated another PCB.  This one works, except there's an annoying, very audible, switching noise that I don't want.  Any ideas how to get rid of that?

I'll try and replace LM5021 with my elderly starting to shake hands!  Haha!  Hopefully it will come good.  I'll get back to you with a result.  Thank you!

What are the conditions under which the noise occurs (input voltage and load current)?

input voltage is AUS mains 240V AC, 50Hz. 2 load conditions initially tested.  no load was loud noise!  then 16-Ohm load was pretty much just as bad.  A bit disappointing.  Would be great if I could get rid of the operational noise.  ideas?

Hi Mark,

Did you use the exact parts from the BOM (especially the transformer) to build your boards? 

thanks,

Brian

yes I did.  I received the transformers from Renco directly.  Thanks.

Seems like a stability issue.  To trouble-shoot, can you provide scope pictures of the output voltage (ac coupled) during the two load conditions?  Also, please provide scope picture of the anode of the output diode (D2), which will show us the switching behavior.