Power Supply Ultra-Wide range Input AC Voltage

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I want to design a power supply for Input=20VAC to 250VAC and 2 Output floating,1st output 5V@0.2A,2nd output 24V@0.12A using TNY266PN or TNY280PN. PI-Expert is giving problem : input is less than the minimum limit of 25. Please help me to design my circuit.

Pi Expert requires a minimum voltage of 25 VAC to complete the design. You will have to use PIXls to compute your design

In your case you have a 20 VAC input. This is too low an input to do a 5 W output design. There are 2 problems that may arise
1) In order to keep the input DC bus abouve 20 VDC you will need a really big input cap (about 150 uF or so)
2) Reduce VOR to below 20 V to avoid the drain node ringing below ground.
3) The value of the inductance has to be very small so that the current limit is reached within the specified duty cycle
4) I suggest that you use the TNY279 part in reduced current limit. The lower inductance will cause a current limit overshoot so operation in reduced current limit mode guarantees that you are far away from the SOA limit of the device.
5) Finally, use a floating current source to source current into the BP pin to enable it to start-up at low voltages. See DI 152 for how this is implemented.
6) Attaching a first pass design. I have only used 1 output but allocated all the power to it. Its just something you can get an idea from...
Mind you - there will be warnings and info messages on this design as it is unconventional...

How can I get the attach refered in "6"?


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