TNY274: Parasitic switching cycles at very low load
Posted by: Namo
on
At very low load, I can see some damped pulses in between switching pulses of the internal MOSFET of TNY274. They only occur at very light load, when there is a quite long time between two switching pulses. Is it a TNY274 specific known issue or do I have to check my design?
When operating at medium load up to maximum load, everything looks fine like the figures in the datasheet on page 5.
There are no other sources/circuits which could influence the TNY274 while measuring -- it is a single power supply.
Ch1: D-S voltage TNY274 (Pin_4 to Pin_5, measured with differential probe)
Ch2: blocking voltage of output rectifier diode
Thanks for Posting your question into forum. Every thing looks at medium load and maximum load. But The Vds waveforms doesn't look as expected at Very light load. We are suspecting it might be due to big loop wire running into oscilloscope GND to Source Pin of our TNY274 . Could you please very your Measurement by using Barrell probe or short probe method while measuring VDS. And also if you see still, Could you start decreasing the load from Full to No load and note the load reading where exactly you are seeing this issue. If you still see the issue, please send us the Schematic , Lay out and Transformer design documents and also the measurement procedure.
Regards,
PI-KSAN