ICL7107 to power and test on the same PC SMPS

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
Hello all,

I am using a pc SMPS for making a lab power supply and plan to add a variable output on one of the 12v lines with an lm317 chip. So I also have a plan to integrate a ICL7107 based voltmeter on the variable line, but I would like to know If I can power the chip from the (-5)-0-(+5) lines of the smps and the same time monitor the 12v line will have the variable regulator. I already have a built voltmeter, just want to know if this would work as ICL7107 needs a different line to power it other than the one it is tested on. I am putting this possibilty in case the smps has separate transformer windings for 12 and 5 rather than regulating the 12v line to 5v.

Thanks
 

ErnieM

Joined Apr 24, 2011
8,377
I *think* I get what you want to do. When you say "power" you mean the meter will get its +/-5V power from the same module as supplies the 12V you wish to further regulate down to a smaller voltage. The meter reads this smaller voltage.

Yep, that should work fine, as everything coming out of the pc SMPS has the same ground. If you had separate supplies then you would have to add the connection to common up the grounds.
 

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
Thanks for your reply.

Actually, you got the good part of my question :) The other part is that, the chip I use in my voltmeter module, *cannot* use the same supply as what it will be measuring to supply the power for running itself, i.e, +/-5V!

And I would like to know if the 12v and 5v supplies coming from a PC SMPS are isolated from each other (except for ground which is common) and the 5v is not derived from 12v using a regulator or other means. Hope you got what I asked. The purpose is to provide supply voltage for icl7107 from 5v as well as enable it to measure its 12v!! Could I get some idea on this please?
 

R!f@@

Joined Apr 2, 2009
9,918
There is no Isolation in a PC supply whatsoever besides input & output.
In a PC supply all the voltages are separate and derived from it's own tx winding.

I believe u won't have a problem in powering the voltmeter while measuring one of it's output.
 

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
There is no Isolation in a PC supply whatsoever besides input & output.
In a PC supply all the voltages are separate and derived from it's own tx winding.

I believe u won't have a problem in powering the voltmeter while measuring one of it's output.
I happened to get this ckt diagram for a 200w pc smps.. from what i can make out of this, it seems to me that the 12v and 5v lines are seperate!! Could anybody verify this please?

 
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