Please give a suggestion

hii this is sanket verma,can u please help me out with the design of 5v,2A and 5v,8A SMPS design.....

Hi Galaban,

The current waveform you show it is actually a voltage waveform. To measure Drain current you have to physically interrupt the connection between Drain of TNY280 ant the rest of the circuits and insert the current probe between the Drain and the circuit.
The very low AC input voltage is supplied trough an extra floating current source. This is because the standard part is not supposed to work with that low voltage. You have to complete the design spreadsheet with minimum 60Vac input voltage for example and minimum 47uF for the filter capacitor. Make sure you address any warning in the design. At the end, you will be able to go to 18Vac input voltage using the floating current source, but you still have to increase the input filter capacitor, maybe close to 100uF. This is something for you to determine on the bench, the input voltage ripple should not be too big for 18Vac input; otherwise the output can loose regulation. Also, it is possible you have to increase the maximum current limit in order to be able to deliver full power from 18vac. I see from your xls file a very low value for VOR. I would recommend some value higher; maybe over 80V (it is related to primary side voltage increase and ringing).
The single mechanism for this part to be destroyed is trough overvoltage. You have to measure the drain voltage for maximum Vac input. If this voltage increases to dangerous levels (close to 700V) you have to redesign the clamp circuit. If changing the clamp capacitor to 4.7nF and the discharge resistor to 250k still does not limit the drain voltage to safe values, use a zenner clamp circuit (check our examples for zenner clamp, or use PI Expert to get an optimized design)

Cheers,
PI_Crusher

Hi Crusher,

what I have attached previously which is current wave form only,Top one is Vds & bottom one is Ids,moreover we have increased the input capacitor still the performance like previous(The drain current beyond the device current limit,Can you give the transformer design. and the schematics should be like DI-152,DeviceTNY280PN,Output=3.3v @ 1.2A,Input Voltage 18-265Vac.
Please suggest which clamp zener we can provide P6ke100 or p6ke200.

Hi Galaban,

I already gave you the transformer design. Just follow the response you received, the capacitor change was only the last point you had to verify. Open your design file and follow step by step the instructions.

Cheers,
PI_Crusher