600 V, 105 mOhm, 29 A — the power MOSFET that defined a generation
The STFI34NM60N: These ratings place it in the high-voltage switching class used in power supplies, lighting ballasts, and industrial converters where the through-hole I2PAKFP package (TO-281) provides a low-thermal-resistance path to a heatsink.
The 600 V, 105 mOhm, 29 A ratings and the I2PAKFP footprint are the key parameters to match when selecting a substitute.
Gate charge and input capacitance — switching loss drivers
The STFI34NM60N specifies a maximum gate charge of 84 nC at 10 V and an input capacitance of 2722 pF at 100 V drain-source. These numbers drive the gate-drive power requirement and the switching transition times. A gate-drive source capable of sourcing and sinking 84 nC per cycle at the target frequency is needed; the 2722 pF Ciss also sets the Miller plateau duration. For a hard-switched converter at 100 kHz, the switching losses will be moderate — budget the gate-drive losses accordingly.