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Old 04-02-2013, 05:35 PM #17
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Default Re: [HELP]High Power 808nm driver

I hope I don't appear too noob here (since I don't fully understand the circuit. Only been doing pure analogues), but if you're worried about current surge to turn on a MOSFET, I don't think it should be much of a concern. Gate-Source capacitances are usually in single to double digit picofarads, and hence the spike, if any, is extremely short lived and won't cause enough power dissipation anywhere to burnout anything.


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Old 04-02-2013, 06:04 PM #18
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Default Re: [HELP]High Power 808nm driver

the pass mosfet above would have nanofarads of gate capacitance and yes, an mcu port will struggle badly with it at high switching rates. M2 is tiny and im pretty certain that nearly any mcu can drive it with or without gate resistor.
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Old 04-02-2013, 08:09 PM #19
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Default Re: [HELP]High Power 808nm driver

It's good practice to put a gate resistor on a mosfet. You can get away with not using one in many cases, but adding stress to components in the name of omitting a 0.1 cent part doesn't make sense to me.
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Old 04-03-2013, 03:33 PM #20
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Default Re: [HELP]High Power 808nm driver

depending on their design, some controller outputs may fail to set or clear if vy large capacitance is present there, so yes, a simple series resistor will add some safety margin.
however: if switching speed is of paramount importance and if conduction losses have to remain low, adding too much resistance on the gate will no doubt cause heat issues. Even 5ohms /preceded by a mosfet driver/ in series with the gate can cause notable slowdown in power mosfets. The lack of one, on the other hand, might result in MHz oscillations if the gate track is long...also, when paralleling mosfets, ferrite beads on the gate or small resistors should definitely be used.
if mr. Phoenix is in doubt of the loading capabilities of his controller and is inclined to experiment, the totem pole mosfet driver is a very simple thing to try out, even if one not needed in the circuit above
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