power supply

[electros6]

hi guys,
           I am working on a power supply. I have attached the schematics herewith.
 basically the power transistor is fed from a constant current source . The conduction of the transistor is controlled by a opamp comparator using LM358.  Everything works fine. I have two issues.

 1)   when the power supply is loaded by 500ma the output voltage drops by around 200mv. The opamp is not correcting it.
2)  The output of the potential divider for  sense , drops by more than 4 times even though the power supply output drops by only 200mv as said above
   eg)   at 5 volt the potential divider out is 453mv but when it is loaded the putput voltage is around 4.83v by the potential divider output is drops to around 110mv
  please help me

[uwezi]

What's the positive supply voltage of your opamp?

While the LM358 includes its own negative supply (GND in single supply configuration) in both its input and output ranges, this is not the case for the positive supply voltage.

However, the voltage of your output potential divider should of course always be 1/11 of the actual output voltage. This means for an output drop of 200 mV it should drop something like 18 mV. For 5 V at the output it must show 455 mV and for 4.8 V it must show 436 mV.

If "it drops by more than 4 times" than something is wrong there! Or with the input of the opamp.