From: Byron Jeff <byronjeff@clayton.edu>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sat, 12 Sep 2020 10:15:57 -0700
Subject: Re: Driving P-channel mosfet. [EE]
Thread-Topic: Driving P-channel mosfet. [EE]
Thread-Index: AdaJKd8bmHJYn7wEQiCTTQtr51jOAA==
Message-ID: <20200912171557.GA5541@clayton.edu>
References:
 <CAFo_nNr4Z=4vyCGWECxWAoh13f5+KwKZUN7Sq9NFe8E8GRrgfw@mail.gmail.com>
In-Reply-To:
 <CAFo_nNr4Z=4vyCGWECxWAoh13f5+KwKZUN7Sq9NFe8E8GRrgfw@mail.gmail.com>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: Pass
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: Pass (protection.outlook.com: domain of clayton.edu designates
	168.28.240.17 as permitted sender) receiver=protection.outlook.com;
	client-ip=168.28.240.17; helo=smtp.int.clayton.edu;
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=clayton.edu; s=csuk;
	t=1599930957; bh=n9FrIwN0SqLWWJ5gtAKcPyLpV8Ihf521+5stN5AXSIQ=;
	h=Date:From:To:Subject:References:In-Reply-To:From;
	b=iFGnyEuxSTreKl93aaRZ1AoLzD1ch3VetsSNZZCxnj5Zzd0y3WIyhTSxWux25l15s
	PvUCXDXzli4rt7d4F52RpUv6tgnJyC9/3jmtt9cY24xflxx2QWEG5zfASlT1+MO4to
	FMb4MJampPq0Nj4lVM7sYOV0jx3DuCWeaXnR0KnE=
authentication-results: spf=pass (sender IP is 168.28.240.17)
	smtp.mailfrom=clayton.edu; mit.edu; dkim=pass (signature was verified)
	header.d=clayton.edu; mit.edu;	dmarc=pass action=none
 header.from=clayton.edu; 
user-agent: Mutt/1.5.24 (2015-08-30)
errors-to: piclist-bounces@mit.edu
list-id: "Microcontroller discussion list - Public." <piclist.mit.edu>
list-post: <mailto:piclist@mit.edu>
x-beenthere: piclist@mit.edu
x-mailman-version: 2.1.6
x-topics: [EE]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

PIC output maxes out at 25ma. You're swinging the line by 5V.
V=3DIR so R=3DV/I =3D 5/0.025 =3D 200 ohms.

Personally I wouldn't trust using the PIC's internal resistance to limit
the current. The primary purpose of the resistor is to set the speed of the
gate since it functions as a capacitor. So the lower the resistance, the
faster the gate charges/discharges.

So, put something in the ballpark of 200 ohms and everything should be
fine.

BAJ

On Sat, Sep 12, 2020 at 04:59:08PM +0100, David C Brown wrote:
> I am planning to use a P mosfet -  type TP0606 -  as a high side switch f=
or
> an LED display.  Everything at  5v.  The gate will be driven by a PIC
> output.
>=20
> Do I need a resistor between PIC and gate, and if so what value?
> On t'internet I have seen circuits which don't use a resistor, circuits
> which use 100E and circuits that use 10K
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: dcb.home@gmail.com
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>=20
>=20
>=20
> *Sent from my etch-a-sketch*
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

--=20
Byron A. Jeff
Associate Professor: Department of Computer Science and Information Technol=
ogy
College of Information and Mathematical Sciences
Clayton State University
http://faculty.clayton.edu/bjeff
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.