# Constant current

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#### PRBS

Does anyone can help me how to implement constant current on BOSOZ?

#### djk

With reference to this figure: http://www.aussieamplifiers.com/se-sch.htm "If I want to creat 40 mA constant current, how should I do?" R8,9 cause Q3 to turn on.When the voltage across R10 reaches the base/emitter threshold voltage of Q4 the current becomes constant.Thus a beV of 0.6V divided by an R10 of 10 ohms would give 60mA.

#### PRBS

Thank you djk, I understood that already.

Does the gain of that circuit reflects R1+R2 divided by R3+R4?
That means, 2k ohms/440 ohms aorund 4.55. Am I right?

#### Jens

Alternatively, use four LM317 with 30R resistors (for ~40mA) between pin Adj.(1) and Out(2), connect pin In(3) to the S of Q1/Q2 and pin Adj(1) to R17 (-V). That’s all.

Jens

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