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[DPRG] MOSFET gate charge

Subject: [DPRG] MOSFET gate charge
From: Ray Xu rayxu123 at gmail.com
Date: Sun Jul 12 23:57:54 CDT 2009

Hi group,

I have one quick question that I can barely find any info on on the web:
What exactly is the MOSFET Gate charge?

My situation here is that I'm building a op amp current source circuit for a
laser diode controller, with the MOSFET "driving" the laser diode; sourcing
current into the diode.  However, when simulating my current source circuit,
I find that N-Type enhancement MOSFETs with different on resistances (self
explanatory) and different Gate Charge values will either output the correct
current, or just output some other current that is far off than the
calculated current supposed to be outputted.  I'm using MOSFETs since
they're more precise than BJTs (less leakage current, etc).

>From what I read so far, the Gate Charge is the required amount of charge
when a transient is present (?? Doesn't make any sense to me).

Any enlightenment would be appreciated.

Ray Xu
rayxu123 at gmail.com
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