positve and negative power supply

[Sean Bartholomew]

thanks guys.
i like the zener diode idea. how can i ensure that the + current
remains greater than the negative current? a 10k R?
if everything else falls short my plan with the 2 regs can work.
incidentally, the diagram shows a 7805. but i need FOUR volts to get a
+5V supply. remember, 9-5=4. thats why im using a 337T cause the 7904
doesnt exist. i wish it did though.

 

[Fred Bloggs]

thanks guys.
i like the zener diode idea. how can i ensure that the + current
remains greater than the negative current? a 10k R?

If you are talking about the 7805 and 4.7V zener combination, then the
COMMON terminal of the 7805 will supply enough bias current for the
zener. Keep in mind that the zener will sink this current plus the +5V
load current minus the 4V load current.