[SOLVED] Role of transistor in a define Current Source

[ehsantech]

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?

 

[:Dark_Force]

The transistor is used to adjust the resistance of the lower branch to equal the ratio "R3/(R_load+R_on) = R1/R2"

 

[ehsantech]

Thank you dear ark_Force
could you tell me the circuit reaction if the ratio wasn't equal?

 

[THINKER_KAM_MAN]

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.

 

[:Dark_Force]

the circuit works to keep the voltage at the base constant in that case

I think its much more the emitter voltage that is beeing held constant by varying the base current!

 

[ehsantech]

Thank you so much for your explanation.

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 ark_Force I didn't know what is more important in resistor relationship ratio? could you tell me more?

 

[:Dark_Force]

Check this out: **broken link removed**