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This is from a 3.5" hard drive enclosure that I am tempted to throw away since I don't have a plug. What likely influenced the design choice to use this sort of plug? The hard drive itself likely takes 12V DC as that is what a computer has.

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  • \$\begingroup\$ What I mean is why this connector over the seemingly ubiquitous jacks that come with switching power supplies? \$\endgroup\$ – user391339 Oct 8 '14 at 6:19
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    \$\begingroup\$ Looks like a mini DIN 4 pin connector. \$\endgroup\$ – MarkU Oct 8 '14 at 6:54
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    \$\begingroup\$ It's used because it was cheaper for the manufacturer to buy a +12V & +5V power supply then a +12V power supply, and use a DC-DC converter internally to generate the +5V from the +12V. \$\endgroup\$ – Connor Wolf Oct 8 '14 at 9:10
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3.5" computer drives, like hard drives or CD/DVD drives, all require +12V AND +5V to operate. In both IDE/PATA and SATA flavors. It's part of the standard. Since computers are expected to have both available through its power supply, disk manufacturers won't bother adding switching supplies to their boards.

As to why the enclosure manufacturer used that dual 12V/5V connector is for the same reason, to supply the needed voltages to the drive inside. Even if you bought the case with drive, the manufacturer might switch disk brands due to manufacturing or supply reasons, and they need to make sure that it works with whatever supply they already chose. It is also cheaper to go with an off the warehouse low amperage dual supply, then designing/sourcing a DC/DC step down regulator and needing a higher amperage 12V supply. Plus, size/space constraints. As well as heat constraints (passive cooling cases especially) And replacing an external supply is cheaper for warranty then having to replace internals etc etc. A variety of reasons.

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  • \$\begingroup\$ This is my guess - dual-rail 5v/12v bricks are likely available mass-produced for cheaper than they can put their own power supply in the unit, and that also means their unit can be smaller & run cooler. I have a couple of HDD enclosures with this connector and a couple with just 12v, all are equally crappy. \$\endgroup\$ – John U Oct 8 '14 at 15:20
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From a technical perspective, there is no advantage over a standard barrel-jack, except for that you can distribute two voltages with this connector. The power connectors in a computer carry both 5V (red) and 12V (yellow), as the label on the enclosure indicates, these are the voltages also required here.

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