EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: veryevil on January 09, 2013, 03:27:26 pm
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Hey, I just got my first two uCurrents and first time out I think I killed one! Switched it to nA range while drawing about 9uA. Now the voltage output is all screwy (technical term).
What do I need to replace to get it working again? Just the MAX4239? Will I have damaged anything else?
Is there any over voltage protection that could be placed on the input of the MAX4239?
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I don't think there's much proteciton on it because it will screw with the burden voltage which needs to stay low.
But perhaps something can be done.
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I assume that the diagram at the http://alternatezone.com/electronics/ucurrent/uCurrentArticle.pdf (http://alternatezone.com/electronics/ucurrent/uCurrentArticle.pdf) is valid.
As far as I'm willing to guess, the Max4239ASA+ has blown. Good news is that it's merely couple USD and SO-8 pin out should be user replaceable, if one has any experience of surface mount rework.
For the future, adding couple protection diodes (from max4239 pin 3 to supply rails) could perhaps prevent similar mistakes. And as far as I understand those should not affect the normal measurement.
Anyone willing to test on their uCurrent ?
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:palm:
Hey, I just got my first two uCurrents and first time out I think I killed one! Switched it to nA range while drawing about 9uA. Now the voltage output is all screwy (technical term).
What do I need to replace to get it working again? Just the MAX4239? Will I have damaged anything else?
Why would switching it to nA-range kill it?
All you're doing is switching from 10kOhm + 10 Ohm to just the 10kOhm sense resistor.
That'd make the voltage output all screwy, but only until you change it back to uA range, it shouldn't kill anything?
(disclaimer: I haven't had enough coffee to do a decent impersonation of awake yet... )
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Why would switching it to nA-range kill it?
My guess is that 8uA is 8000nA which is 8 times higher than the 1000nA input range and also is trying to set 8v output.
I have no problem with replacing the chips SMD on this scale is easy. Its just which bits, pretty sure just the MAX chip.