This　paper　presents　a　buck　type　dc-dc　converter　for　uA/mA-scale　solar　cells　under　low　light　intensity　conditions.　The　maximum　power　point　tracking　and　voltage　regulation　are　achieved　with　single　stage　DC-DC　conversion.　The　proposed　system　is　designed　and　simulated　in　a　0.1.8um　CMOS　technology-.　The　proposed　circuits　conduct　voltage　tracking　and　regulation　based　on　input&output　voltage.　It　utilizes　a　PID　closed　loop　and　hysteresis　voltage　band　to　control　the　PWM　on　power　MOSFETs.　In　this　design,　the　dc-dc　converter　dynamically　controls　the　solar　cell　to　operate　at　the　maximum　power　point　with　a　0.64%　error　and　obtains　an　output　voltage　of　1.8　V　with　a　0.2%　ripple.　A　conversion　efficiency　of　92.5%　on　capacitor　Cl　at　300uAinput　current　and　an　end-to-end　efficiency　of　68.4%　are　achieved　in　simulation　through　using　the　input　and　output　bi-directional　closed-loop　control　method.