View irf840a datasheet:

PD- 91900A SMPS MOSFET IRF840A HEXFET® Power MOSFET Applications VDSS Rds(on) max ID Switch Mode Power Supply ( SMPS ) Uninterruptable Power Supply 500V 0.85? 8.0A High speed power switching Benefits Low Gate Charge Qg results in Simple Drive Requirement Improved Gate, Avalanche and dynamic dv/dt Ruggedness Fully Characterized Capacitance and Avalanche Voltage and Current G D S TO-220AB Effective Coss Specified (See AN1001) Absolute Maximum Ratings Parameter Max. Units ID @ TC = 25°C Continuous Drain Current, VGS @ 10V 8.0 ID @ TC = 100°C Continuous Drain Current, VGS @ 10V 5.1 A IDM Pulsed Drain Current 32 PD @TC = 25°C Power Dissipation 125 W Linear Derating Factor 1.0 W/°C VGS Gate-to-Source Voltage ± 30 V dv/dt Peak Diode Recovery dv/dt 5.0 V/ns TJ Op