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Old 05-11-2012, 09:37 PM #1
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Default Low-Voltage Op-Amps....

Hey everyone. I am going to crowd-source this one because I can't seem to find any!

All of the current-sensing op-amps I seem to find are only capable of working with an input voltage (before the sense resistor) of more than 1.6V or so. I need one that can work down to .1V. I can supply the op-amp with a separate power supply (5V or whatever), but I need it to be able to sense currents through a low voltage, but it doesn't seem like there are any!

Help me people! I am working on designing a nice, switching power supply for you folks


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Old 05-11-2012, 10:23 PM #2
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Default Re: Low-Voltage Op-Amps....

You don't need a current sensing op amp. You just need a sense resistor to convert the current into voltage. I think you need to look for one with "common mode input" that goes down to v-.
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Old 05-11-2012, 10:30 PM #3
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Default Re: Low-Voltage Op-Amps....

I know I don't need one. However, an op-amp with adjustable gain means I can use a pot to adjust current fully (meaning its a lot better for end-users) and I would have more efficiency, meaning less expensive parts (i.e. smaller transformer necessary).
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Old 05-18-2012, 12:12 AM #4
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Default Re: Low-Voltage Op-Amps....

What would be the point of making a seperate supply for the opamp? I'm certain it can be done, but there are plenty of opamps available with common mode range right down to the negative rail.

The 'default' 741/TL071-like opamps will not do you any good there, but sometimes there is a good reason not to stick with ancient components.
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Old 05-18-2012, 12:13 AM #5
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Default Re: Low-Voltage Op-Amps....

Not a separate supply. But I want to be able to have it sensing a current across one rail and supplied by another rail.
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Old 05-18-2012, 03:46 AM #6
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Default Re: Low-Voltage Op-Amps....

I believe you want to use a rail-to-rail op amp then Wolf.

It's a specification that op amps use for things like what you're looking for.
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