lab power supply

[[email protected]]

hi to all
i'm an italian electronics hobbyist,
i'm sorry for my bad english
in this holiday i try to build my first lab fully adjustable power
supply unit
i try to hack the scheme at pag.8 of the datasheet of the lm317
http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF
for add the negative section,
the tracking voltage mode,
the transistor for increase the output current,
and a costant current output protection..
i ' ve implemented 5V reference due to start the regulation from 0V
instead of 1.2V (normal limit of an LM317)
i would like to use an lm705 for the 5 volt reference using this
voltage for an ausiliary power supply for TTL boards
i obtained this basic principle scheme , not yet dimensionated
i will have an opinion about eventual problem or improvements
http://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE7B.pdf
thanks to all for the patience

 

[MooseFET]

hi to all
i'm an italian electronics hobbyist,
i'm sorry for my bad english
in this holiday i try to build my first lab fully adjustable power
supply unit
i try to hack the scheme at pag.8 of the datasheet of the lm317http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF
for add the negative section,
the tracking voltage mode,
the transistor for increase the output current,
and a costant current output protection..
i ' ve implemented 5V reference due to start the regulation from 0V
instead of 1.2V (normal limit of an LM317)
i would like to use an lm705 for the 5 volt reference using this
voltage for an ausiliary power supply for TTL boards
i obtained this basic principle scheme , not yet dimensionated
i will have an opinion about eventual problem or improvementshttp://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE7B.pdf
thanks to all for the patience

ASCII ART:
Sense
! !
---------- --+-/\/-+--
! \ /e R2 !
! --- !
! R1 ! R3 !
+-/\/\- --+--/\/\------+
! e\ / !
! --- !
! ! !
----+-/\/\/--+--! LM317 !-----+------------
R4


R1 makes the transistor's E-B drop less important so temperature has
less effect on the performance.

Moving the R3 connection does the same for the other transistor at no
cost in parts.

You have Q24 flipped.

What are ypou trying to do with Q26?

 

[[email protected]]

ASCII ART:
Sense
! !
---------- --+-/\/-+--
! \ /e R2 !
! --- !
! R1 ! R3 !
+-/\/\- --+--/\/\------+
! e\ / !
! --- !
! ! !
----+-/\/\/--+--! LM317 !-----+------------
R4

R1 makes the transistor's E-B drop less important so temperature has
less effect on the performance.

Moving the R3 connection does the same for the other transistor at no
cost in parts.

You have Q24 flipped.

What are ypou trying to do with Q26?

when r108*imax it becomes approximately equal to the Q26 Vbe,
Q26 is turned on ,it short circuit R109 and then switch off Q25 and it
limits
therefore the output current
http://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf
pag.23 fig.13

what do you think about of the current regulator?
you have some idea to avoid to use a double potenziometer for the
current adjust?
we could be taking advantage of the advanced operational U2A

this is the updated scheme:
http://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE7C.pdf

 

[[email protected]]

when r108*imax it becomes approximately equal to the Q26 Vbe,
Q26 is turned on ,it short circuit R109 and then switch off Q25 and it
limits
therefore the output currenthttp://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf
pag.23 fig.13

what do you think about of the current regulator?
you have some idea to avoid to use a double potenziometer for the
current adjust?
we could be taking advantage of the advanced operational U2A

this is the updated scheme:http://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE7C.pdf

Sorry MooseFET I have mistaken to copy!
excuse me! the problem is that in Italy it is late night
and I am distracted of nature
now I understand why the regolator did not seem correct!
many thanks!!
I have corrected the scheme from many errors
this is the new one link
http://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE8.pdf
aspect suggestions in particular for the regulation of the current
thanks to all!

 

[MooseFET]

Sorry MooseFET I have mistaken to copy!
excuse me! the problem is that in Italy it is late night
and I am distracted of nature
now I understand why the regolator did not seem correct!
many thanks!!
I have corrected the scheme from many errors
this is the new one linkhttp://dunsscoto2.googlepages.com/SCHEMATIC1_PAGE8.pdf
aspect suggestions in particular for the regulation of the current
thanks to all!

I don't like what you have done with R4. Transistors should not be
uses such that their HFE matters. You want an emitter resistor and
not a base resistor. The has an indirect effect on the current limit
issue.

I worry that the current limit circuit will overshoot, ring and do
other bad things. When the current limit is not active, the LM358
will have its output as high as it can manage. This is bad.

A diode or the like on the LM358 so that it never tries to take its
output all the way up would help to make the current limit engage more
quickly.