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Questions about curve tracer

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lokeycmos

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hello fellow enthusiasts! i have a couple questions about a curve tracer circuit also known as "octopus". i found a similar transformer but with different voltages i will be selecting via a rotory switch. the voltages are: 3, 4.5, 6, 9, and 12. the transformer i found is rated for 300ma. my question is about the current limiting resistor and pot. im trying to figure out what the maximum amount of current i should use so i can find the appropriate resistor/pot combination. with the schematic using my transformer with the 12 volt tap and a 560 ohm resistor its only putting out 21ma. im not sure if this is sufficient or not or if i should use a smaller resistor to put out a little more current.the reason im asking is because i want to make this device as general purpose, and universal as possible. any help or advice would be appreciated.
 
Not knowing what components you may be testing makes it difficult to suggest your needed values.

You might want to compare your circuit to for your design.

Somewhat more complicated but with the necessary current control circuitry.
 
Did you pinch the tranny out of a wall wart then?
It wont work exactly as the schematic you posted will however the differences will be small, try it, unless your comparing results from another octipus I think itll be fine.
My beckman scope had a component tester built in, the voltage and current were fixed I think about 3v and 5mA.
Heres a couple of designs, the first uses resistors to generate the volatges rather than transformer taps, and the second link shows you why its called an octipus (or at least thats how I know it).
Seems that wall wart transformers produce a distorted circle with this type of circuit.

https://pe2bz.philpem.me.uk/Power/- LV/Site-900-WallXformers/octopus.html

https://www.qsl.net/kd7rem/octopus.html
 
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