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finding short on motherboards with a shorty (with display)

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kripton2035:
why not, but for me not a drawer component I have around, easier to get 2 ex of some basic silicon diode ?

Kean:

--- Quote from: wacd on March 13, 2024, 04:35:54 pm ---How abour this CMJA5050

https://my.centralsemi.com/datasheets/CMJA5050.PDF

--- End quote ---

Did you review the datasheet for that part?

It has a 10% tolerance, takes over 10 seconds to come into regulation, and has a TC of -0.3mA/degC.
It is not a precision part, and it also seems to need a supply of 8V or so to regulate.

wacd:
Okay, how do i limit the current to 50mA then?
These are the results when i use the lab psu limited at 0.05A its almost perfect.

Kean:

--- Quote from: wacd on March 14, 2024, 05:38:22 am ---Okay, how do i limit the current to 50mA then?
These are the results when i use the lab psu limited at 0.05A its almost perfect.

--- End quote ---

If you want precision, I would suggest changing the design to use an opamp controlled current source.  https://en.wikipedia.org/wiki/Current_source#Op-amp_current_sources

So, looking at the original Shorty schematic, R3 would be the sense resistor and selected for higher precision, and R1 would be replaced with a transistor controlled by the opamp.  R2 and the DUT become the load.  Assuming R3 stays at 1 ohm, you would need a voltage reference (the 5V or 3.3V rail may be OK) and divider to get the 50mV reference.  Opamp would have to be selected for a low offset voltage.

wacd:
Thank you for providing information. I'll go and spend some time on this to learn it better so i can implement it , hopefully :)

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