First of all tx for the response, it's appreciated!


> >I would like to drive a SFP9520 FET (or alternate)
> >(24VDC, 800mA) >I'm considering adding a small FET
> >stage if required to drive this larger FET.
> >I have omitted the filtering op-amps circuit to try
> >to get this circuit functioning. The input to this FET
> >circuit now is 5volts rail to rail PWM 20kHz from the
> >(pic driven)
>>-------------------------------
Alan B. Pearce wrote:
<<<<< First thing is that the FET is not going to saturate with a 5V gate
drive. On page 2 of the data sheet, check the Rds(on) value, it is given
with 10V gate drive. This is typical gate drive for most FET's unless they
are  classed as logic level devices. Logic level devices tend to have other
limitations such as higher Rds(on) values.

To check if you can get a low enough Rds(on) check figure 6. This would
suggest you are going to have about 2V across the FET at 0.8A current with
5V gate voltage.

The other thing that I suspect is stopping your circuit is how you drive the
gate. This looks like a large capacitor to your circuit, so if you are
trying to switch it fast, you will need a heavier current drive than the
opto can give you.>>>>>
>-------------------------------------------
My new question:  The input (available) to this driving [FET(s)] circuit now
is 5 volts rail to rail from the opto-coupler.  This is the stage I need
help with.  Perhaps an IRLD110 FET as a intermediary stage between the opto
and the main FET could be used.
From the opto coupler's output, can I drive a smaller FET to provide proper
gate drive to the larger FET, then in turn offering 24VDC out.
Still require help with the driving circuit for this valve.
Regards, {slewrate}
http://www.irf.com/product-info/datasheets/data/irld110.pdf

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