The RB521SM-40 from ROHM Semiconductor is a Power Diode with Forward Current 0.2 A, Forward Voltage 0.3 to 0.54 V, Reverse Current 3.5 to 90 uA, Reverse Voltage 40 V, Repetitive Peak Reverse Voltage 45 V. Tags: Surface Mount. More details for RB521SM-40 can be seen below.