Basically, I have dc adapters one of 12v 2a and one of 5v 1a, which do not have short circuit protection, having said that I want to make a simple circuit to protect them, I will add the circuit to the dc output cable of the charger so as not to disassemble it, I have seen various types of short circuit protection, for example:

With Buzzer, Those who trigger sound when short-circuited and throw away said energy so that it does not return. something like 19v 4 amp adapters.

Resumable silent, which cuts the power when there is a short circuit and resumes the passage of power until a few seconds pass, disconnected from the electricity of the house.

With led indicator, those that make the led turn off when there is a short circuit and stop the power while there is a short circuit, and resume until the short circuit stops. turning on the led again.

Using fuses, which blow when shorted and can be replaced.

I'm basically interested in any of those, except the last one, the one with replaceable fuses.

Or if there is another, for example using a diode that absorbs all the energy when the switch is short-circuited.

Here the dc adapter 12v 2a, using a switch to cause the short circuit:

enter image description here

Here the dc adapter 5v 2a, using a switch to cause the short circuit:

enter image description here

How much more simple and effective is, is better for me...

Led diodes ot buzzers are optionals

For the people who comment about the nippon adapters, I leave these images, in case they help in something!

enter image description here

enter image description here

  • \$\begingroup\$ Perhaps you are looking for a resettable fuse. \$\endgroup\$ Jun 19, 2021 at 21:05
  • \$\begingroup\$ any very common that you can recommend? \$\endgroup\$
    – Antelmoo
    Jun 19, 2021 at 21:06
  • 1
    \$\begingroup\$ Could it be simpler to buy adapters with short circuit protection? Actually, why are you sure your existing adapters don't have protection? \$\endgroup\$
    – Justme
    Jun 19, 2021 at 21:12
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    \$\begingroup\$ I would contact Nippon to verify. A consumer adapter wouldn't last very long if it couldn't survive a short-circuit on its output. Especially when it's pictured with one of those CCTV barrel to screw terminal adaptors: nipponamerica.com/product-page/dv-2005 \$\endgroup\$
    – ErikR
    Jun 19, 2021 at 21:38
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    \$\begingroup\$ Those look like pretty casual switch mode power supplies. These usually can handle short circuits just fine, so it would be uncommon if these didn't. What do you expect to happen if you short circuit these power supplies? \$\endgroup\$
    – Justme
    Jun 19, 2021 at 22:18

1 Answer 1


Any power supply rated for "input: AC 100~240V" must be a switch-mode type, which always have some kind of overload protection. Supplies designed to work with chargers generally have a current limiter which holds current down to (or close to) the rating, while general purpose supplies often have 'fold-back' protection which reduces current to a low value or turns off completely when current exceeds the limit.

Linear power supplies often only have a thermal fuse embedded in the mains frequency transformer, and rely on resistance of the transformer windings and rectifier circuit to survive momentary short circuits. You don't see many of these today because they are large, heavy, inefficient and have very poor regulation with high ripple. These units are only designed to work on a narrow voltage range (eg. "100~120V"), unless they have a switch to select different primary windings for different mains voltages.

Some linear power supplies have a regulator (linear or switching) on the low voltage side to provide the more stable voltage required for sensitive equipment, and these do have current limiting. If a linear supply is regulated it will usually be stated on the label. If not you can tell by measuring the open-circuit output voltage, which will be close to its rating (whereas unregulated supplies can be up to 50% higher).


Thank you for uploading the image of the inside of your adapter. We see the controller IC is a DK-124, which has "Over current, Over loading, Over temperature, Over voltage and Short circuit Protection". Section 9.8 of the datasheet says:-

Whenever the collector current (Ip) abnormally exceeds the maximum current limit of 1.3A, the controller would stop operation and enters into stop status.

This suggests the power supply will shut down when overloaded.

  • \$\begingroup\$ If any of these dc adapters have thermal fuse embedded, i not want kill it, thats why i looking for a way to protect these adapters, because my purpose of i buy these adapters are do test of short circuits. \$\endgroup\$
    – Antelmoo
    Jun 19, 2021 at 23:44
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    \$\begingroup\$ Only linear supplies with mains frequency transformers have thermal fuses, which are designed to blow if the transformer gets too hot or is run on a much higher voltage than normal (eg. 120V transformer on 230V). Your adapters are switching types. They should limit current or shut down quicker than a correctly rated fuse would blow. Using a fuse for secondary protect while testing should be fine, because it shouldn't blow. \$\endgroup\$ Jun 20, 2021 at 0:12
  • \$\begingroup\$ thanks by the information, add some images that could be useful, so that you guide me, what PPTC fuse can i use for 5v 2a? and what PPTC fuse can i use for 12v 2a, if you may know? \$\endgroup\$
    – Antelmoo
    Jun 20, 2021 at 0:18
  • \$\begingroup\$ "This suggests the power supply will shut down when overloaded." It means my adapter will not die if i made a short circuit in the output by a long time, right? \$\endgroup\$
    – Antelmoo
    Jun 20, 2021 at 0:33
  • \$\begingroup\$ Correct, if it does it what it says then it should not die. So the only question is - do you trust it? I wouldn't want to use a switching power supply that couldn't handle being short-circuited. But since you are testing it, why not test it to find what happens when you make a 'long time' short-circuit? If it shuts off, and then restarts when the short is removed or with a power cycle, then it's all good. \$\endgroup\$ Jun 20, 2021 at 0:52

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