Sorry for the short subject line; I got hit by the forum subject line bug!
I tried to make it: Very Small Power Supply (millivolt) question

If I have a non-isolated power supply such as this one:
http://www.power-one.com/sites/power-one.com/files/documents/power/datasheet/yev09t03_v5.pdf
Operating at no more than 10 milliamps,

Programmed to output 2 volts

And I externally applied 4 volts to the output, say, with a potentiometer,
with a common supply and ground,

What would happen to the power supply?
Would it damage something?
Or just stop operating?

 

Absolutely nothing, the output will be fixed.
The quoted power supply is spec'd for 20A so I'd be more worried about only drawing milliamps from such a high power supply, though it looks like it will be ok. Probably rather expensive for what you are doing though.
I suspect there's more to this than you have said so I await further info to reveal what the real problem develops into.

 

I've been looking around a bit, maybe this one may be more suitable:
http://www.mouser.com/ds/2/330/yev09t03_v5-19301.pdf

Spec'd for 3 amps. From what you said in your post,
I probably wouldn't have to use a diode to prevent "backflow."

I have a variable voltage supply, but I can't set the minimum voltage.
The minimum "is what it is."
So I want to maintain a minimum voltage using a separate power supply.
Then when the variable voltage rises above the power supply voltage,
I just need to make sure that I won't damage the power supply with reverse voltage.

 

What are you actually trying to do?

It looks like you are trying to have a backup power supply. Most people join two power supplies together with two diodes if they want redundant/backup supplies.

 

I'm not sure how to explain it better than that.

I have a 5V line voltage, feeding a Hall-effect sensor.
The minimum voltage of the sensor signal is 1.5 volts, and I can't vary that.
And I can't add a diode to it, because of the voltage drop.
Under certain circumstances, I want the signal to be 2.15 volts.
I'm thinking I can do that with a DC-DC converter (power supply) in parallel.
I am not worried about the DC-DC hurting the Hall-effect sensor, I'm told by the mfr. that won't be a problem.
What I don't know is if, when the Hall-effect sensor is putting out more than 2.15 volts,
the higher voltage will damage the DC-DC converter. THAT I can add a diode to, if necessary,
and just adjust the output of the DC-DC to compensate for the voltage drop.
Thanks for your help,
--Clipper

 

If you posted a diagram of the connections, we could better help you with your question.

Depending upon the power supply design you could likely put a diode in series with the output but inside the regulation loop (voltage sense point after the diode) so the diode drop is automatically compensated.

 

I'm not sure how to explain it better than that.

I have a 5V line voltage, feeding a Hall-effect sensor.
The minimum voltage of the sensor signal is 1.5 volts, and I can't vary that.
And I can't add a diode to it, because of the voltage drop.
Under certain circumstances, I want the signal to be 2.15 volts.
I'm thinking I can do that with a DC-DC converter (power supply) in parallel.
I am not worried about the DC-DC hurting the Hall-effect sensor, I'm told by the mfr. that won't be a problem.
What I don't know is if, when the Hall-effect sensor is putting out more than 2.15 volts,
the higher voltage will damage the DC-DC converter. THAT I can add a diode to, if necessary,
and just adjust the output of the DC-DC to compensate for the voltage drop.
Thanks for your help,
--Clipper

So now there's a Hall effect sensor, the mystery continues. It sounds like you are trying to amplify the sensor output to a maximum of 2.15V for some reason. So I say again either tell us what you are actually trying to do or don't expect to get any useful help. What happened to the original power supply question?

 

Hello,

This seems to be a continuation of the automotive thread I closed some days ago:
Two Hall-effect sensors in parallel?

As automotive modifications are not allowed on this site, I will close it again.

Bertus

PS when you start a new thread on the same subject, a ban may follow.