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Please consider the following circuit where voltage sources V1 and V2 are regulated linear DC power supplies:

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From the simulation V1 will sink 2.5A of current provided by V2.

Questions: What will happen to V1 in this situation? Would it go into some sort of default operation or will it "happily" sink the current? How does this change for switch mode supplies?

Now suppose we eliminated resistor R1 such that V1 is directly shorted to 10V.

enter image description here

Questions: Would this be considered an "overvoltage" condition for V1? What is the response of V1? I understand that decent supplies will have overvoltage protection which will shutoff its output (via SCR, etc), but does it protect for conditions where the DUT is higher voltage that the regulated output?

Thanks

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  • \$\begingroup\$ Do you know what happens if you boost car battery that is low in voltage? yet all batteries have a series R \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 8 '16 at 18:21
  • \$\begingroup\$ Of course, but the response of a regulated DC power supply is different from (rechargeable) batteries. \$\endgroup\$ – user25955 Oct 8 '16 at 18:31
  • \$\begingroup\$ all regulated supplies have ESR too \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 8 '16 at 18:38
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What will happen to V1 in this situation? Would it go into some sort of default operation or will it "happily" sink the current? How does this change for switch mode supplies?>

If V1 is a typical series linear regulator (such as an LM7805 or LM317) it will not sink current and remain in regulation. Instead the output voltage will rise. Some current will most likely flow back into the 5 V regulator, but how much depends on details of the design of the regulator; for example, what kind of pass element it has and whether it has some reverse-current protection circuit.

It is possible to design a linear power supply that can handle this situation, but it would essentially just be a big op-amp circuit.

Now suppose we eliminated resistor R1 such that V1 is directly shorted to 10V. Would this be considered an "overvoltage" condition for V1?

This is not what would normally be called an over-voltage condition. Overvoltage for a linear regulator typically means applying too high a voltage to its input terminal.

Applying any voltage higher than the programmed output voltage to the output terminal is still a fault, but in a different category. Typically called a reverse-power fault or a reverse-current fault.

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