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Do I need the 100 ohm resistor in the below circuit? Is there any problem if I don't use it?

wiring diagram

SamGibson
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Suny
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    What are you going to use this for? Are you aware that the DC Out 12 V will be live? – Transistor Jul 02 '19 at 17:08
  • For 12v led strip – Suny Jul 02 '19 at 17:10
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    you could get a bridge and capacitor damaging inrush current. You should use at least an X2 for that mains connected cap. – Neil_UK Jul 02 '19 at 17:11
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    Those 12 V strips generally don't have adequate insulation to protect the user from electric shock. You need an isolated power supply for that so this one is not suitable. I suspect that you haven't worked out what current you need. That will be a problem with this power supply too. Get a proper 12 V isolated PSU with an adequate current rating. – Transistor Jul 02 '19 at 17:14
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    If you're asking that, then you should not be building transformerless power supplies until you know more. They're dangerous. – DKNguyen Jul 02 '19 at 17:21
  • @Suny This is Sunny. What is your real problem and real load? ( Hot parts ?) – Tony Stewart EE75 Jul 02 '19 at 17:31
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    Death trap 101! – winny Jul 02 '19 at 17:31
  • Not if enclosed properly for some load TBD? – Tony Stewart EE75 Jul 02 '19 at 17:34
  • You are not explaining in 4?5? questions how you are misusing this circuit.. If Zener is too low power and no load, then it can fuse open, then Cap fails out from over voltage and shorts,but hot resistor is normal if open and abnormal if safely enclosed but then improperly derated for temp rise. – Tony Stewart EE75 Jul 02 '19 at 17:38
  • It is very safe unless you make an error in completing the design correctly – Tony Stewart EE75 Jul 02 '19 at 17:40
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    @SunnyskyguyEE75 No, this is not "very safe". It is very unsafe. There is no isolation between mains and the output -- at 220V it's an absolute death trap. –  Jul 02 '19 at 17:52
  • @Clipboard_Waving_Enginerd "Most likely" is not a very good comment when there are lethal voltages involved. When questions like this show a general lack of knowledge we try to err on the side of safety with our comments and answers, as you can see from those who followed you. – Elliot Alderson Jul 02 '19 at 18:31
  • @ElliotAlderson Good point thank you. I deleted the comment. To Suny you could use one of the ubiquitous 12V power bricks everyone has a drawer full of. Better yet buy a 12V supply for the LED strip, Use this question as your guide. – Some Sorta EE Jul 02 '19 at 20:11

2 Answers2

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Yes, you need it.

If you don't have it, some part of your circuit will burn out and be destroyed. Which part will actually go "poof" or "bang" first can't really be predicted.

You've been told before, but I'm going to tell you again:

That circuit can kill you.

You must operate that thing in an enclosed box.

Do not allow any user to touch any electrical part of that thing when it is operating.

If you connect the output of that thing to another device, then that device can now kill you, and should be enclosed when operating.

You must assume all parts of that thing to be at line voltage.

You should find a safer powersupply circuit to build.

JRE
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  • To elaborate... You need it because it is limiting inrush current. When you plug this in and the capacitors are empty, they will act as short circuits until they are full. That 100ohm resistor limits that initial current spike.

    PS. This will kill you.

     – Stiddily Jul 02 '19 at 18:43
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    @Stiddily: That resistor is constantly limiting current. An earlier question from the same person asks why that 5 watt resistor is getting too hot to touch. So, it isn't just the inrush current. – JRE Jul 02 '19 at 18:46
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There is a lot of PACKAGING INFO that you are not telling us that lead up to your overheating failures. All parts serve a different purpose.

But with the right parts, in the right thermally convection air-cooled, but double-insulated behind the wall along with your LEDs or loads out of harm's way, it can be safe, but packaging design is not shown. I suspect with the care taken in your schematic, that the heat-rise in packaging lead to cascaded infant failures.

If done wrong such as reversing line and Neutral and touch LED "0V", or common mode transient... poof! zap!.

This shows you the actual REACTIVE and REAL power of each part. enter image description here

This design lacks:

  • thermal packaging, electrical insulation design
  • PLT Power Line Transient protection.
  • fusing
  • technical analysis and adequate engineering details in question

But still can be made to work!

Tony Stewart EE75
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