| Electronics > Metrology |
| Precision current source single Mosfet or twin transistor setup? |
| << < (4/5) > >> |
| Kleinstein:
Another way for a 1/10 voltage divider is using 6 equal resistors as 3 in series and 3 in parallel. With some matching this can give a rather good accuracy and low TC even with not so good resistors to start with. There are now also ready made dividers in SOT23 and similar small size. |
| iMo:
What "precision" do you actually target with that above circuit? |
| Overspeed:
Hello Question is for who ? in my case I need to run 4 points resistivity measurement so I need to be ''better'' than Keithley 6220 , but as not a programmable value bu a fixed value better can be reachable . I also don't want to fall under 10 Volt to reach acceptable power level . tests / measurements are 10 minutes so i don t need 1 year bomb proof stability too as far I am stable . I link the Keithley 6220 data table for information 100 mA is not amazing I have not the budget for new/calibrated 6220 and I don't need all functions of the 6220 too , just a robust accurate ( stable and precise ) 100 mA source for low to very low resistance material , primary idea was to built a zlymex or a Eevblog current source ( 1 amp) tuned to 100 mA , current source recipe don t look to be NASA rocket science as first is to have a stable and accurate voltage ref as ref54 / ref80 or other with a precision op amp and precision low tempco resistor. Regards OS |
| Kleinstein:
For a resistance measurement one likely would not need the high settling speed of the 6220 and not much current programming other than maybe on / off / reverse polarity. For a 100 mA range only, the main critical part is the current setting resistor. One would likely want a 4 wire resistor or at least seprate traces directly from the resistor. Depending on the meter used for the voltage reading, one could also consider the variant with the DUT and ref. resistor directly in series and not on different sides of the FET. This version would allow easier switching between the voltage at the DUT and ref. resistor and also an easy polarity switching. However it kind of needs a separate supply, and a ratiometric measurement gets a bit more tricky. Depening on the resistance range a true ratiometric measurement may not be needed - very low resistors (e.g. < 10 mohm) may well have other limitations. |
| iMo:
--- Quote from: Overspeed on January 04, 2025, 06:49:55 pm ---Question is for who ? OS --- End quote --- The Q is for you. You want a precision current source, but except the "100mA" there is none other indication what you actually want (provided this is the Metrology section people wait on some indication). Based on some specific parameters (meaning numbers) people may judge on the actual circuit and parts to be used. |
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