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The design I am working on is having peripheral connector with +5V power in it providing the voltage to the would-be connected device. There's relatively a long way inside the design from the ATX power supply to the connector, with edge connector involved in between.

I am thinking about building some kind of simple protection from the shortage or overcurrent. The ATX PSU can provide enormous amperage, thus it could be a reality that something happening after the peripheral connector will fry the power lines on the way from the ATX power supply.

I know about several ways:

  • fuse. It will blow on overcurrent, and will need to be replaced. For the design, it is not a big issue as it is assumed that owner is able to maintain/repair it;
  • polyfuse (MF-MSMF020 or MF-R020). A kind of multi-fuse, while being convenient has several drawbacks. It seems its "protection time" is larger than of fuse; it heats so that there must be no parts around damaged by the heat (e.g. plastics), and if too much stressed, can eventually increase the resistance, as well as having higher initial resistance than fuse;
  • some electronic protection circuit.

I want to be as simple as possible; and it is ok if fuse is blown and needs to be replaced on the overcurrent event which would be considered as exception rather than a rule.

Thus the answer may be obvious - use 250 mA fuse, ideally socketed. Maybe like this on the Symbios SCSI card.

I can not find part number for such fuse.

And is there any other better way/device to achieve the protection from the external overload?

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  • \$\begingroup\$ Apart from the williness to require a repair, your requirement has a lot of similarity to that of USB host ports. Polyfuses are sold for this, but there are also many active overcurrent chips, too. For a single-shot protection, go to an electronic vendor, select "fuse" select "250 mA" and then select from suitable packages. \$\endgroup\$ – Chris Stratton Dec 2 '19 at 20:33
  • \$\begingroup\$ Also consider a beeper circuit across the fuse, such that the moment the fuse blows, the beeper starts up and thus trains the operator to never do that particular thing again. :) \$\endgroup\$ – rdtsc Dec 2 '19 at 21:03
  • \$\begingroup\$ @ChrisStratton great comment, I am going for TPS2051C. \$\endgroup\$ – Anonymous Dec 3 '19 at 8:56
  • \$\begingroup\$ @rdtsc nice idea! Any part number to start with? The beepers like TKD PS series require rectangular wave input and a driver, but are there any all-in-one devices, so that I apply, say, 5V, and it buzzes at specific frequency? \$\endgroup\$ – Anonymous Dec 3 '19 at 14:19
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A fast blow fuse is your best bet to have a chance at saving electronics in case of a hard short it will also guarantee that the failed circuit is disabled.

Alternatively, active current limiting circuits can be done with discrete components, good PMIC have this function integrated .

A polyfuse or positive thermal coefficient device (PTC) is a convenient device to protect against moderate but chronic overcurrents. E.g. on the output of a power supply that is driving too many loads, but is poorer choice for fault conditions.

As you point out the distinct disadvantages for safety shutoff is

  1. Slow trip time measured in seconds instead of milli seconds
  2. Slow recovery (up to 24hrs) during which field diagnosis and behavior may be poorly characterized
  3. Recovery itself may exaccerbate the issue, fault occurs device shuts off, next day some one tries again more damage, risne and repeat until there is no hope to repair the fault.
  4. Can have false positive trip from elevated ambient or local temperature
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