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I have built a link switch.

The output is DC 5V but, when measured with an oscilloscope, itis not constant.

Why does this happen?

How do I get constant DC output?

Any design problem?

enter image description here

datasheet link switch

Output voltage:

Output wave form much noisy ..so i will updated soon

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    \$\begingroup\$ To answer this question, you need to show the load (it requires a load for stability) and the PCB layout. Show where you have the probes attached on the oscilloscope, that can make a huge difference. \$\endgroup\$ – Voltage Spike Jul 26 '19 at 4:59
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    \$\begingroup\$ @VoltageSpike i am create this circuit in general purpose PCB (similar to circuit diagram) \$\endgroup\$ – Shavan We Jul 26 '19 at 6:10
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    \$\begingroup\$ Also, please show your probe setup. Dave at EEVblog made a video about how important a good probe technique is for output ripple measurements. \$\endgroup\$ – winny Jul 26 '19 at 8:27
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    \$\begingroup\$ Are you using a mains-frequency isolation transformer for this non-isolated circuit? Unless you're using that or an isolated probe or internally isolated oscilloscope with high CMRR there's a lot of potential (pun intended) for problems. \$\endgroup\$ – Spehro Pefhany Jul 26 '19 at 13:23
  • \$\begingroup\$ You need to answer the questions asked to you if you want a answer. \$\endgroup\$ – winny Aug 6 '19 at 7:07
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The LNK302 datasheet that you linked recommends that you change R4 to 2.4Kohms or less if the circuit has zero load.

enter image description here

enter image description here

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  • \$\begingroup\$ same issue still exist \$\endgroup\$ – Shavan We Aug 5 '19 at 6:14

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