Hi Jan-erik,
I am switching at 80khz.  So it sounds that without the resistor there is a
risk of over loading the pic but with the resistor there is a chance of
overheating the mosfet. :)

I actually checked the archives  before I breadboarded the circuit and found
both posts advocating and not the series resistor.

Thanks,
Gregory

> -----Original Message-----
> From: Jan-erik Soderholm (QAC) [mailto:Jan-erik.Soderholm@PAC.ERICSSON.SE]
> Sent: Wednesday, April 23, 2003 3:49 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: PIC driving a mosFET...driver chip or a FET?
>
> Gregory A. Pruden wrote:
> > I am using an IRLZ34 and when using a series resistor...
> > made the MOSFET quite hot in comparison to using it without the series
> > resistor.
>
> Are you switching with a "high" freq ?
> Say, 10-100kHz and up ?
>
> The MOSFET probably dissipates the most heat
> when beeing someware in between hard "off" and hard "on".
>
> Having a resistor in series with the gate, will make the
> charging time of the gate capacitance to be longer
> then when driving it directly, and also the time the
> MOSFET stays between hard "on" and "off". So you want the
> FET to switch as fast as possible, which is does
> when driven directly without the resistor (or a "low" value res).
>
> Well, sounds logical to me, at least...
>
> > What is the purpose of the series resistor
>
> To protect whatever is driving the MOSFET from high currents. I'd
> expect larger MOSFET's to have larger gate capacitance, and you could
> reach a point when the current spikes gets to large (for e.g. a PIC port).
>
> > and what was I doing wrong?
>
> Depends on what you *intended* to be doing... :-)
>
> Regards
> Jan-Erik Soderholm.
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics