Low Cost non-isolated Power Supply - to replace simple RC supply | 荷兰帕沃英蒂格盛有限公司 (Power Integrations)

Low Cost non-isolated Power Supply - to replace simple RC supply

Posted by: MAC Limerick on 01/21/2009

I'm looking at the possibility of using an LNK306 as a cheap non-isolated 5V supply. The problem with my existing RC supply is that it only goes to 20mA and I now need 50mA - 200mA source. One of my design requirements is that the PSU must withstand 418VAC for 48hours, otherwise it is 85VAC - 265VAC.
Looking at a reference design like that shown in Fig 5 of the datasheet, can the LNK withstand 418V AC ! If not is there another option. ! Appreciate comments.

418VAC sounds like a three phase outlet.....when rectified that gives 600V DC which is below the LNK306 fet limit of 700V. as long as your freewheel diode turns on quickly enough after the fet turns off it should be ok...mabe you will need some clamp or snubber to be sure you dont threaten the 700V situation. but it sounds like you want a buck.....but you duty cycle will be terribly low........5/600 = less than 1 percent.....so i bet the fet doesnt even come on in that short time......so its maybe a no go-er unless you use a tapped buck, like in some powerint literature. also, with 600V , if you use buck, just imagine how quick your current will rise when the fet turns on.....will the current sense in the lnk306 be quick enough to catch it before it gets ruinously high??

Hello MAC,

treez was kind to respond to your post and he is right, you can use LNK306 for your application with 418Vac input . Just make sure you use components rated for this voltage level, you have the proper spacing between high voltage traces (do you have to comply with regulatory requirements?), and your chip does not go too hot. It is possible to get some extra heat working at 600Vdc input, if necessary use a PCB area as a heatsink or a small heatsink wing soldered directly to the four source (S) pins.

Cheers,
PI_Crusher

Thank all for the feedback.....appreciate it...looks like it is worth evaluating this as a design option. The 418V for 48H is a possible failure state of the single phase...and the good part is that the power supply/unit need not work during this period, only survive. As the load current is likely to be low, a few mA (only 200mA when charging Li-Poly Batt), any extra heat hopefully should not be a problem. Regulatory requirements are required. Not a power expert...any reference design for 4.5V

Hello MAC,

You can check this design:
http://www.powerint.com/sites/default/files/PDFFiles/der47.pdf or go to this page: http://www.powerint.com/en/design-support/reference-designs/design-examples and browse any buck with LNK30x. You can not replicate one schematic with no changes at all, you have to use one as a starting point and make necessary changes for your input/output parameters.

Cheers,
PI_Crusher

Low Cost non-isolated Power Supply - to replace simple RC supply

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