data sheet of what?
the zener diode? or the 741?
both of them use less then 240uA -s oit should work o.k.

Well, the zener needs min 5mA to stay in regulation.

The 741 input min bias current needs to be observed in the datasheet.

 

so I will need at least R1=25K to make it work ?

and I have seen in the datasheet of the 741 Ibias(typical)=80nA
so it's good right?

 

25K for the zener diode?

Nah it would be much lower than that.

Use formula:

RZ = (VCC - ZV) / IT

Whereas:

RZ is the droping resistor for the zener
VCC is the supply voltage
ZV is the voltage rating of the zener
IT is the desired current through the zener

 

so it should be
(12-6.2)/5mA=1.2K

 

so it should be
(12-6.2)/5mA=1.2K

Yes. But as the supply drops this will change.
So perhaps allow a bit more current. But you'll get away with 1.2K

Personally, I would use an precision voltage reference chip, not the zener.

Try IC TLC431.

These are nice and cheap on eBay. There is billions of them.

 

I didn't find it on ebay
and also if I will use it - that mean more wire to use and more space
I need the smallest circuit i can build

Thanks !
I will buy the parts and let you know if it's work

Thanks,