Here's some information about it:

Current and Voltage Rating: The "1.5A 1000V" designation indicates that the diode can handle a maximum average forward current of 1.5 amps (hence the "1.5A") and a maximum reverse voltage of 1000 volts (hence the "1000V").

Rectification: Like other rectifier diodes, the 1N5399 is primarily used for rectification, converting alternating current (AC) into direct current (DC) in electronic circuits.

Package Type: The 1N5399 diode typically comes in an axial package, which is a cylindrical package with leads on each end. This package type allows for easy through-hole mounting on a printed circuit board.

Forward Voltage Drop: The forward voltage drop of the 1N5399 diode is typically around 1 volt when conducting forward current within its rated specifications. This voltage drop determines the power dissipation and efficiency of the diode in a circuit.

Reverse Recovery Time: The 1N5399 diode has a relatively long reverse recovery time compared to Schottky diodes, which makes it suitable for lower-frequency applications but may not be ideal for high-frequency circuits where fast switching is required.