There are many kinds of diode . For example , Schottky Diode , LED ( Light Emitting Diode ) , Photo Diode , Laser Diode , Varactor Diode , Current Regulator Diode , PIN Diode , Tunnel Diode , Step Recovery Diode , IMPATT Diode , etc. The use of the diode equation in circuit problems is illustrated in the article on diode modeling .