Couple of questions regarding the negative supply:
Why is it required
Why only used on U3
Isn't there a lot of ripple on it?
U1 has an output of +11.2V and its inputs are at +5.6V so it does not need a negative supply.
U2 has an output that goes as low as +1.0V and has inputs that work at 0V so it does not need a negative supply.
U3 is the current regulator. It works by reducing the output voltage so that the output current is what is set on the current-setting pot. In order to reduce the output current when the output is shorted then the output voltage of U3 must go to -0.7V because of the voltage drop across D9.
Then the output voltage can be reduced to 0V.
So U3 has a -1.3V negative supply.
I don't think the negative supply has much ripple because its load current is only a couple of mA. Besides, U3 is not affected by a little ripple.