TLC7135: Floating Power Source + Earth Ground Current Sense?

Fred Doe

Part Number: TLC7135

I am designing a 0-3A power supply with a possibly earth ground connection. I would like to keep the supply connected to earth ground if possible. I am using the TLC7135 differential input A/D digital display driver and a sense resistor in a panel meter with a low-side current return ( I'm not calling it ground for sake of clarity) to measure the supply's current. The power source for this supply is floating and thus has no particular potential to earth ground. I could adapt the panel meter to measure the high-side current but a low-side current sense would be much easier. Ultimately my question is: Can I connect the power supply's output to earth ground and still have the panel meter measure the return current to the floating power source accurately and reliably?

over 4 years ago

0 Tom Hendrick over 4 years ago

TI__Guru**** 168485 points

Hi Fred,

Is it possible to share a schematic of what it is that you are trying to do? If I understand correctly, you may run the risk of exceeding the input voltage range to the TLC7135 with the floating supply.

0 Fred Doe over 4 years ago in reply to Tom Hendrick

Intellectual 655 points

Here is the schematic. If it is not readable please let me know. The pins that are not connected in the schematic would make the schematic more convoluted so I left them blank; in the final application they would be connected as the typical application circuits show the display and 2V full scale etc. For the rest of the circuit see in https://www.renesas.com/us/en/www/doc/datasheet/icl7135.pdf the Typical Application Schematic and the schematic in Figure 7, other than the Vref, and the specific use of ground symbols. By the way, the +-5V supply is relative to the 24V floating supply with the 0V of the floating supply being the same as the 0V of the +-5V supply. Also, the +-5V is floating too, as shown it is like batteries. (But it is standard DC Regulated supply https://media.digikey.com/pdf/Data%20Sheets/Mean%20Well%20PDF's/SCWN06,DCWN06_Series_Ds.pdf DCWN06B-05 It is powered by the 24V supply.)

0 Fred Doe over 4 years ago in reply to Fred Doe

Intellectual 655 points

Is there anything wrong with this, is it illegible or anything? I know it is hand written mostly but think it is reasonably legible and all that. Is this in the wrong forum? Am I not supposed to do external links like the power supply datasheet? If any of this is so please let me know.

0 Tom Hendrick over 4 years ago in reply to Fred Doe

TI__Guru**** 168485 points

Hi Fred,

Sorry for the delay - with the 'floating supply return' acting as the "ground reference" for the circuit (your 5V and 24V), you should be fine. I don't have any issue with that.

0 Fred Doe over 4 years ago in reply to Tom Hendrick

Intellectual 655 points

Alright, thank you so much for your help!

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TLC7135: Floating Power Source + Earth Ground Current Sense?