The CMPF4391 BK from Central Semiconductor is a Junction Field Effect Transistor (JFET) with Drain Saturation Current 50 to 150 mA, Gate Source Voltage 40 V, Drain Source Resistance 30 Ohm, Gate Current 50 mA, Gate Reverse Current 0.5 nA. Tags: Surface Mount. More details for CMPF4391 BK can be seen below.