Correctly designing with LinkSwitch-TN for high-power non-isolated design...

2 posts / 0 new
Hi, I intend to use the “LinkSwitch-TN” part for usage in a non-isolated power supply to deliver 15V @ 360mA (into a buck switcher that in turn generates 3.3V @ ~1.3A into a mostly resistive load). Reading the datasheets, the reference designs and the LinkSwitch-TN app note (AN-37), I believe the ‘high-side buck / direct feedback’ topology in ‘Continuous Conduction Mode’ (CCM) is most appropriate. However, three important questions remain. Q1: Will the ‘LinkSwitch-TN’ power supply function correctly if Live & Neutral are inverted? Q2: The application has to control an AC load using a Triac (dim 60W light bulb). AN-37 on page 1 mentions “LinkSwitch-TN can be configured in all common topologies to give a line or neutral referenced output and an inverted or non-inverted output voltage – ideal for applications using triacs for AC load control” It is unclear if ‘inverted’ or ‘non-inverted’ is compatible with Triac designs. Which topology is most recommended to correctly drive a Triac? Finally (for another design), I intend to use the same LNK306 part to maximize its power draw... While playing with the “PI Expert Product Selector Guide”, I noticed that the LinkSwitch-TN LNK306 part is still recommended for a power supply that outputs 50 VDC @ 360mA. That is 18 watts of power extracted from the mains without a transformer! Can the part really pull that off? (Is there a reference design that shows how to do this safely?) I played around with PIXI and set Cin to 150uF with part dissipating .81 watts of heat. Are there resources available that show how to extract this much power safely out of this part? Many thanks for any advice / hints you can offer!! Jean-Pierre Poulin
Yes, non-isolted converters for LNK-TN can be reference either to line or neutral However the noraml output polarity for buck will be positive and for buck-boost it will be negative. If you invert from the normal polarity for the assoiciated topology you will break the tie to the mains (either line or neutral)which is usually not desirable. For second question, yes, 50VDC@360mA will work provided you have adequated heatsinking by having using large enough copper area around source connection to serve as heatsink. Also part is restricted to 65% duty factor so there is a min voltage restriction. The input bulk cap must be sufficeintly large to reduce Vmin at 85VAC (I am assuming theis is your min AC applied voltage)