When connected an external voltage to vout of this 5v regulator, the chip get very hot. I connected a 4v to its Vout, and it draws 500ma. The protection diode from vout to vin doesn't help. My doubt is that I also have 3 different labels for this voltage regulator: They are AMS1117-1225L, AMS1117-H505KE and AMS1117-H1418. I have tested all three. Only the 1225L will over-heat and draw 500ma. Other 2 are just okay. WHY!? is this 1225L an older device? I can't find any datasheet about it either. another question is, I want to add a 5v input to the vout of the AMS1117 5.0v, do I need a protection diode between my 5v input and this vout?

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    \$\begingroup\$ Why are you connecting an external voltage to the output of the regulator? What are you expecting to happen? \$\endgroup\$ – Roger Rowland Oct 29 '15 at 19:00
  • \$\begingroup\$ For complex and multiple Vin arrangements I'd consider having a buck-boost regulator fed from a common input point with the individual inputs wire-orred. \$\endgroup\$ – Andy aka Oct 29 '15 at 21:20

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