That 723

[<<marjan>>]

Hi ,

> Thank you, but pin6 is not the output voltage, it is a referance voltage.
> The chip is a variable power supply. It does this by comparing a voltage against
> a reference voltage, available on pin 6. The current available for this
> comparison is 15mA. So designers need to keep this current in mind when, say,
> calculating the values for a resistor divider.
> eg two 10 ohm resistors in series will give a volage at their juntion of 0.5Vref
> but will draw way too much current (about 375 mA).

Hey,nice explain in few sentences,thank you.

And sorry,my mistake - 723 in eti is can casing and I had datasheet for
plasic dip.
Totaly different pins.
So now,it says it gives some 150mA (in free air ?) output for plastic
(and other)
casings.No mention of heatsinks.So it'll work?



> Yes, and if I wanted to redesign the power supply and rebuild it on a different
> board, that is an option. 

don't want to bother you but they look pretty same to me,put 7805
in,gnd,out pins in
723's positions 7,1,2, ditch C3,D5,R3,R4,RV1,
raise R1 to 22k,lower R11 to 4k7,on place of pin 10 of 723 put 33u cap
to gnd and base
of npn,emit to gnd,col. to pin3 of ic2,3 ,also 10uF to gnd from that
point,
cut track that connects that junction(pin 3 ic2,3) to 7805's out and
connect them via 10k.
Connect pin9 where 723 was (end of R11) to base of Q2 ,mount 7805 on
heatsink.
Other parts of psu are the same.

>However I would prefer to explore the choices and
> hopefully find a quicker cheaper and easier solution. 

So try plastic casing 723.If it heats too much,try something else.

<I'm basicall lazy :-) >

huh,we all are ;)

once more sorry for confusion


marjan