LNK304 SMPS design - Page 1
Forum section: electronics / projects

author: LukeW
author_rank: Frequent Contributor
timestamp: April 10, 2013, 06:41:43 am
content: Edit: Resolved

author: LukeW
author_rank: Frequent Contributor
timestamp: April 12, 2013, 08:56:18 am
content: Nobody?Well, I built an initial prototype to test... and it failed on power-on, blowing the 8.2? fusible input resistor. (Which is why it's there, though.)After reviewing everything, the RS1M fast diodes I had in stock are fast, but they're not ultrafast which probably really doesn't help things. I think I'll replace it with something ultrafast in an SMA package such as an ES1J and see what happens.

author: Ibra
author_rank: Newbie
timestamp: April 16, 2013, 08:05:33 pm
content: Hello LukeW,unfortunately I am not able to help you but I would like to ask you for hint.I have the LNK304 device on board by 3rd party. This board does not work properly. I have measured cca 40 Ohm between source and drain pin of LNK304 (in OFF-state, without voltage connected). Does it mean that this LNK304 device has a defect (I would assume higher resistance between Drain and Source in the OFF state) and I have to replace this position by new device?Thanks a lot in advance,Best regards, Ibra

author: LukeW
author_rank: Frequent Contributor
timestamp: January 01, 2014, 11:58:24 am
content: For the future reference of other readers, the circuit mentioned in the original post does work, although I made a few component substitutions. The basic circuit architecture is unchanged.In particular, I think the only really important changes were to bring down the inductance of L2 down a little bit to 680 uH, and to substitute D3 for an ultrafast diode with the smallest reverse recovery time you can find, this diode is fairly critical.The other component changes are not really important, they're pretty flexible and not critical.L1: 1 mH, Bourns RLB0914-102KLL2: 680 uH, Abracon AIUR-02H-681KC2, C3: 4.7uF 400V, Rubycon 400PX4R7MEFCTA8X11.5R3: 8R2 2W fusible, Yageo FKN200JR-73-8R2D1, D2: 1000V 1A general purpose rectifier, Diodes Inc S1M-13-FR1: 4k7 1% 0.1WR2: 2k0 1% 0.1WC4: 0.1uF 50VC1: 10uF 10V, 0805 ceramicR5 removed.D3: Fairchild ES1J, ultrafastC5: 100uF 1206 10V SMD tantalum, but an aluminium electrolytic would also work just fine at a lower price. Voltage rating should be at least 10V.

author: TheGreatGooglyMoogly
author_rank: Contributor
timestamp: January 02, 2014, 02:15:59 am
content: Luke,I was looking at the datasheet for the LNK304 and it looks like your schematic is missing a rectifier diode. Look at Figure 5 in the datasheet and it has a 1N4007 on the neutral line as well as the hot line. I'm not familiar with these chips, but that diode might be blocking something nasty going into the chip and thus the chip may be kaput on your prototype as well... Interesting chip, I may have to pick one upEdit missed your last post somehow

author: LukeW
author_rank: Frequent Contributor
timestamp: January 06, 2014, 06:38:15 pm
content: I did that on purpose because I wanted the DC ground to be tied directly to the mains neutral. (In some other application contexts, depending on what you're doing, eg. current sensing or triac control, you may want the local DC ground tied to the mains active.)It still works fine without that second diode.