Drive a MOSFET via BJT?
This is called "push pull output configuration" and provides unity voltage gain but significantly low output impedance and high output current. This makes push/pull output ideal for driving high capacitive loads such as power MOSFET gates at relatively high frequencies when the driver (IC or MCU) cannot source enough current --widely used in switching converters (Personally, I'm using this config in my 2-sw Forward and 2-sw Flyback converter designs). No need to place two separate resistors, btw:







simulate this circuit &ndash; Schematic created using CircuitLab

Note that VCC and Vi should be at the same level for proper on/off switching. If, for example, VCC = 12V and Vi = 5V, this circuit cannot perform its job.

PS: IRF840 is not a logic-level gate MOSFET, IRL840 is.