Even i was having same problem in second year of my engineering, hence i wil try to explain u a bit what i have understood last year..
gate drive (in this case is a bidirectional current source, which can control the limits for gate current, which in turn can control the slew rate of power amplifier.
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All power semiconductor devices need gate pulses to get turned ON.
There r circuits which trigger pulses to those gates, these ve to be controlled to maintain the slew rate v desire. Then some power semiconductor devices such as SCR can be switched ON by a gate pulse nd cannot be switched OFF by any means other than itself attaining zero current condition. If these like devices r used then v need to control everything. So, Gate drivers are used in amplifiers.
INS-ANI had the best info so far the gate driver does 2 importent things it turns the driver on/off if it's a switch or controls how on if it's linear [never off], the 2nd job it does is to prevent changes in gate/drain voltage from affecting gate/source voltage since a power fet looks like 2 capacitors in series bypassed by a wildly variable current leak.
BTW for junction transistor outputs this circuits a "pre-driver".