I designed Step up boost converter using 555 pwm ic for variable DC voltage, output voltage varies from 0-300 Volt.I have to design constant current limiting circuit at the output of boost converter which limits the current to 1 micro ampere.The purpose of this current limiting circuit is if short happens at load side then boost converter will not send current greater than 1 micro ampere.Please help me on current limiting part.

 

Put a large value resistor in series?

 

No options are possible without a schematic.