emitter follower design, stuck on basic

[harp]

I try to make basic circuit, and wonder why it not work as expected. I can not fully saturate transistor (try with bd675a and bd139) and circuit only drow about 7mA in both case, not 17mA as I expected. What to do to correct this into functional circuit? The load must be on ground.

[Heisen]

I don't think your circuit can draw 17mA, at max it can draw about 12.5mA, even if we remove the potentiometer.

[eccerr0r]

Heisen is correct (approximately, of course this depends on the actual transistor used). Depending on the ability of the pot, the discrete 139 transistor will probably get more current through than the 675a darlington in your configuration.

Only ways to get more current is to increase your voltage, use common emitter (PNP if needed), or decrease your load resistance;, otherwise you're topology limited.

[stj]

the current flowing is directly related to the base current calculated from the HFE.
if thats intended as a switch you should use a mosfet to minimise thermal losses from the junction resistance.

[harp]

Yes, thank you all... I have just to be sure that there is no some trick