From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sat, 23 May 2020 11:14:27 -0700
Subject: Re: [EE] MOSFET Gate Voltage
Thread-Topic: [EE] MOSFET Gate Voltage
Thread-Index: AdYxL2FErCuolzn0Qt6Iuarw30NDPQ==
Message-ID: <4e48b07d99a1a37468b1b69b6c5d0812.squirrel@mai.hallikainen.org>
References:
 <CAD2N_E_h-0GaD_HVCwGdsd_CuStBPrjF1NCA_oPbSOZSNuyJDQ@mail.gmail.com>
	<CAOFvGD7wEFcLpnY3gZrJbwu6u6CVEHdx96rzjtTssPtUDb-95Q@mail.gmail.com>
In-Reply-To:
 <CAOFvGD7wEFcLpnY3gZrJbwu6u6CVEHdx96rzjtTssPtUDb-95Q@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 mai.hallikainen.org
	designates 208.77.216.252 as permitted sender)
	receiver=protection.outlook.com; client-ip=208.77.216.252;
	helo=mailscanner.virtbiz.com;
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=mitprod.onmicrosoft.com; s=selector2-mitprod-onmicrosoft-com;
	h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;
	bh=NDBaZE4EZimtvisbqS+JfCjKoV+EWOTDe6G01XXfcOQ=;
	b=QFR9mIejPodk7PERpxXzNGpdX/B/i03rQ/H4WOeUHK0in1oX81sdHpvGYXlmRzFBLEUXy1p6dqo7kPROC87Pgy2js6CYIYCkeRzqefJMp9xJ0DP6ba912R0jEnxUwfmDtPjEwxLXl/qcE0aGXLiOjFA+CaeZpLlQ945qo45kc8Y=
authentication-results: spf=pass (sender IP is 208.77.216.252)
	smtp.mailfrom=mai.hallikainen.org; mit.edu;	dkim=none (message not signed)
	header.d=none;mit.edu; dmarc=permerror action=none
	header.from=mai.hallikainen.org;compauth=pass reason=111
user-agent: SquirrelMail/1.4.22-5.el6
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-authentication-warning: mai.hallikainen.org: apache set sender to
	harold@mai.hallikainen.org using -f
x-spam-status: No
x-greylist: IP, sender and recipient auto-whitelisted, not delayed by
	milter-greylist-4.6.2 (mailscanner.virtbiz.com	[208.77.216.252]); Sat, 23
 May 2020 13:14:35 -0500 (CDT)
x-topics: [EE]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

I'd certainly look at the datasheet of the FET. But, in general, I see
nothing wrong with the gate voltage being higher than the drain voltage.
In fact, that is a typical condition once a FET is switched on.

Harold

> I'd advise reducing the control signal to 3.3 volts. Without more
> information it's hard to say what might (or might not) happen.
>
> On Saturday, May 23, 2020, Josh Koffman <joshybear@gmail.com> wrote:
>
>> Hi all,
>>
>> I'm modifying an existing battery powered LED lamp. I haven't fully
>> completed my investigation, but I believe I have identified a MOSFET
>> that is responsible for controlling the LEDs. I want to hijack that
>> MOSFET and inject my own control signal. If my current theories are
>> correct, this shouldn't be too hard.
>>
>> However, the circuit is running off a battery at 3.3V. The control
>> signal I plan on using is going to be 5V. So that means the gate of
>> the MOSFET will have more voltage on it than across D-S. Will this
>> work, or will this end badly for the MOSFET?
>>
>> Thank you!
>>
>> Josh
>> --
>> A common mistake that people make when trying to design something
>> completely foolproof is to underestimate the ingenuity of complete
>> fools.
>>         -Douglas Adams
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>
>
>
> --
> Jason White
> --
> 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
FCC Rules Updated Daily at http://www.hallikainen.com
Not sent from an iPhone.
--=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
.