This part is a kind of semiconductor called 40HF120.

Function of this product has STANDARD RECOVERY DIODES.

Manufacturers : Digitron Semiconductors

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Some of the text within the PDF file :

40HF(R) Series High-reliability discrete products and engineering services since 1977 STANDARD RECOVERY DIODES 40 AMP FEATURES  Available as “HR” (high reliability) screened per MIL-PRF-19500, JANTX level. Add “HR” suffix to base part number.  Available as non-RoHS (Sn/Pb plating), standard, and as RoHS by adding “-PBF” suffix. MAXIMUM RATINGS Parameter Maximum average forward current Maximum RMS forward current Maximum peak, on cycle, non-repetitive forward surge current Maximum I2t for fusing Maximum repetitive peak reverse voltage Junction temperature range Symbol IF(AV) IF(RMS) IFSM I2t VRRM TJ Test Conditions @ 50Hz @ 60Hz @ 50Hz @ 60Hz 40HF(R) 10 to 120 140 to 160 40 @ TC = 140°C 40 @ TC = 110°C 62 570 595 1600 1450 100-1200 1400-1600 -65 to +190 [ ... ]

40HF120 PDF Datasheet Download