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I'm going to use this 12VDC AC/DC power supply . It is the first time that I am going to use one and I have some questions about over voltage protection and peak current protection. These are the questions:

  1. The AC / DC internally has a 1A slow blow fuse. Is it necessary to add an external fuse? Maybe something less than 1A to protect the internal fuse?
  2. Regarding the input overvoltage protection, I have thought to use a varactor. The problem is that I do not know to find the information in the datasheet about the maximum input AC voltage. What characteristics should the varactor have: max. continuous voltage, max. clamping voltage and energy rating? I have found this good explanation (How to choose the right Metal Oxide Varistor (MOV)) but I still do not know how to choose the varactor because I can not find all the information in the AC / DC converter datasheet.

  3. About the output overvoltage protection, I have read this parameter in the datasheet: 'Over Voltage Protection (OVP)' -> '125% - 195%, auto recovery'. I do not understand this parameter well. Should I add a TVS diode to guarantee never to exceed 195% of 12VDC?

Below is a circuit diagram to clarify:

schematic

simulate this circuit – Schematic created using CircuitLab

Thanks.

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Is it necessary to add an external fuse? Maybe something less than 1A to protect the internal fuse?

If the internal fuse blows then it's very likely that it's because the unit has developed a permanent fault. The fuse is present (as it is on most SMPSs) for regulatory reasons.

The input voltage range is rated at 85-264 volts and it will be fine even if this is overloaded by 10 % usually. They also say on their data sheet that there is a CB Report and maybe you could get hold of this just to double check on things. I wouldn't be considering using anything external on the AC side.

'Over Voltage Protection (OVP)' -> '125% - 195%, auto recovery'. I do not understand this parameter well.

This again is likely to be another regulatory feature to prevent unsafe (to humans) output voltages. Normally this type of protection is implemented internally using a crow-bar circuit.

If you can't live with the output rising to potentially 195% of nominal then I'd consider a TVS diode.

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