Markus
The resistor in series with the gate is typically used to prevent
oscillaton at RF frequencies. It may not be required or it may be
essential. Layout is a major factor as well as the type of load and
mosfet characterisics. For the cost, I'd add it. 100ohms is a
reasonable figure but if your switching frequency is high you may want
to drop it somewhat (10 ohms minimum ?)

It does provide some protection to the PIC in the event of device
failure, but that is more a benifit than a reason.

Richard P

On 27/11/06, Markus Rohe <piclist.rohe@gmx.net> wrote:
> Hello everyone,
>
> it must have been an about 4 or 5 years since I backed out of the
> piclist and the world of PICs. Now, a few weeks before Xmas I decided to
> do a new PIC project again.
>
> I have a rather simple question, however, some extensive search on the
> web and www.piclist.com did not delivered enough information for me. I
> plan to drive a few lightbulbs (12V) by a PIC and to minimize a loss of
> energy this should be done with a logic level mosfet. The IRLZ 34N seems
> a good chice for me (Ron=35mOhms, rather cheap and _available_ at my
> local dealer). Now: How to attach this device to a PIC port. An approach
> like this sould do the work:
>
>
>                             bulb
>                              |
> ------                       D
> RBx  |--------------*-----G
> ------              |        S
>                     Z        |
>                 10k Z        |
>                     Z        |
>                     |        |
>                     |        |
>                    GND      GND
>
>
> I am not very familliar with this sort of device (In fact I am only
> hobbyist) something is very confusing to me: In some schematics the
> authors use some low-valued resistors directly befre the gate. I assume
> this is to protect the driving device from some high current pulses when
> the gate has to be charged. Would it be necessary for the PIC as well like
>
>
>                                    bulb
>                                     |
> ------                   100Ohms    D
> RBx  |--------------*----|/\/\|--G
> ------              |               S
>                     Z               |
>                 10k Z               |
>                     Z               |
>                     |               |
>                     |               |
>                    GND             GND
>
> Any hints or web-pointers iwth similar schematics are welcome. If you
> think this generates too much noise over the list, please email me
> privately.
>
>
> Best Regards
> Markus
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