i need a small and cheap power supply. I found the LNK30x Family but i dont know how i have to change the values in the sample circuit to generate 5V 300mA output.

Found also this design Guide http://ac-dc.power.com/sites/default/files/product-docs/an37.pdf

enter image description here

But i don't know how to change the circuit to this values.

Can someone please help me.

  • \$\begingroup\$ This is the circuit i will use, but don't know which things i must change. content.screencast.com/users/Ripper_121/folders/Jing/media/… \$\endgroup\$
    – Ripper121
    Sep 7, 2015 at 8:30
  • \$\begingroup\$ If you have extra information, please edit your question to add it rather than starting a potentially long comments thread. \$\endgroup\$
    – stefandz
    Sep 7, 2015 at 9:47
  • \$\begingroup\$ Can only include one Link/Picture with my reportation. \$\endgroup\$
    – Ripper121
    Sep 9, 2015 at 6:21

2 Answers 2


You can just use the next largest size, LNK306 with the components for Iout(max) = 360mA. When it says 360 it doesn't mean "exactly 360", it means "not more than 360", and so of course you can draw anything between 0 and 360, including your desired 300mA.

Caution: the circuit you show looks like it is supposed to connect to mains voltage based on the input ratings, but it would be extremely unsafe to use in that way, because it doesn't have any galvanic isolation. What's wrong with using a USB power supply? (readily available for $2-3/each, does have isolation, and can produce up to 1A)

  • \$\begingroup\$ I need a very small solution to fit in a small enclosure. I will use the LNK360 but what should i change to get 5V in the shown circuit? \$\endgroup\$
    – Ripper121
    Sep 7, 2015 at 9:01

I changed it to this and it should work.

LNK306 5V

  • \$\begingroup\$ I hope that, if this is plugged into the mains, it is at least in a completely isolated/nonconductive case. You are one 1N4007 diode failure away from having mains AC connected to your circuit ground and (if the case is not isolated) to a person (ouch). I would highly recommend not going this route; among other things, you will never be able to get a UL rating for this design. \$\endgroup\$
    – Alex I
    Sep 8, 2015 at 0:35
  • \$\begingroup\$ You can see how Apple designed their cube charger here: righto.com/2012/05/apple-iphone-charger-teardown-quality.html You can use a similar topology but omit most of the filtering, and use an inductor 1/3 the size (this is most of the volume in this circuit). \$\endgroup\$
    – Alex I
    Sep 8, 2015 at 0:37
  • \$\begingroup\$ This Designe is used in many washing machine. The PCB is in a closed nonconductiv enclosure. \$\endgroup\$
    – Ripper121
    Sep 9, 2015 at 6:17
  • \$\begingroup\$ "The PCB is in a closed nonconductiv enclosure." - is the PCB connected to anything else? Because you are looking at basically getting mains voltage into anything else it is connected to. \$\endgroup\$
    – Alex I
    Sep 9, 2015 at 6:34
  • 2
    \$\begingroup\$ @Ripper121 I haven't reviewed your design but LNK306 is a fine chip. People here are paranoid about safety. I think its enough to warn once and treat fellow members as adults and sensible engineers. It's almost a disease with western engineers that prevents them from going low cost and effectively competing with China. Low cost does not have to mean cutting corners. Some applications just don't need the protection. An apt application for this chip would be to power an IoT led bulb logic circuit. Since the bulb a whole is going to be treated as electrically "hot", no need to isolate the innards \$\endgroup\$
    – Dojo
    Aug 1, 2016 at 12:47

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