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[SOLVED] Role of transistor in a define Current Source

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ehsantech

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Hello
here are two different circuit that the current creator section are the same.if there is no problem could you tell me the role of transistor in current source?
Capture001.JPG
Capture002.JPG
 

The transistor is used to adjust the resistance of the lower branch to equal the ratio "R3/(R_load+R_on) = R1/R2"
 
Thank you dear :Dark_Force
could you tell me the circuit reaction if the ratio wasn't equal?
 

just a suggestion,

i think the transistor is used to enable the load to be connected to the -ve rail. and thus can obtain more current output
the circuit works to keep the voltage at the base constant
in that case; as Ic = Ib+IE,

the divider sets the reference to compare against, and the other resistor is the current monitor resistor.
 
Last edited:
Thank you so much for your explanation.
Code: 
i think the transistor is used to enable the load to be connected to the -ve rail. and thus can obtain more current output
dear THINKER_KAM_MAN as you check the output current it is related to R3 resistor and minimum op-amp input bias
and dear :Dark_Force I didn't know what is more important in resistor relationship ratio? could you tell me more?
 

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