From: Brent Brown <brent@eds.co.nz>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Thu, 12 Aug 2021 16:19:47 -0700
Subject: Re: [EE] PTC fuse voltage
Thread-Topic: [EE] PTC fuse voltage
Thread-Index: AdeP0aZlKDBloAO3R/SwdviDlnMA0g==
Message-ID: <6115AC93.17810.826A67E@brent.eds.co.nz>
References: <8ae670e8-a41f-6ed7-9bd5-97064d56f2f4@narwani.org>
In-Reply-To: <8ae670e8-a41f-6ed7-9bd5-97064d56f2f4@narwani.org>
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: None (protection.outlook.com: eds.co.nz does not designate
	permitted sender hosts)
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=eds-co-nz.20150623.gappssmtp.com; s=20150623;
	h=from:organization:to:date:mime-version:subject:message-id:priority
	:in-reply-to:references:content-transfer-encoding	:content-description;
	bh=/+qfD50rtcT0FJQIKuUH/a3Si0wE7rxC9UfZ1ZBiPn8=;
	b=Pwt1hC0xnieWC4UsgDHj3DCvP3IcawDWLJOtEMcY3GftHYN8hS4E7WtcG+oLThtwrY
	li9WxXeIF0NnjVx4sxy+rld+CB1SAmXlOpxEDL0Qk+kWzOmRNYECPGZ8LKg6kXxHMEzA
	DmtCZlFOArExcRtu40RhbK9P6DHdx6AE0wREsU6s8TlQVPltPjVaL9OYUkNVdk0ITr7F
	tw5iZuS5AwTJj6nIyk4rikoTFbjIz/pzNWKCfxYuLkmLSeqzAAyMLghREdarfl7UICDZ
	2drrZ/HM3DnYl38PXI7VyUlYns7MKfzgGH7Ay5Cvcp6F2R7F+Uew2rlHtY7cf2t3wTDb	oGhA==
authentication-results: spf=none (sender IP is 209.85.216.47)
	smtp.mailfrom=eds.co.nz; mit.edu; dkim=pass (signature was verified)
	header.d=eds-co-nz.20150623.gappssmtp.com; mit.edu;	dmarc=none action=none
 header.from=eds.co.nz;
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-received: by 2002:a17:902:d890:b029:12d:f2:e8d6 with SMTP id
	b16-20020a170902d890b029012d00f2e8d6mr5550878plz.42.1628810391801;	Thu, 12
 Aug 2021 16:19:51 -0700 (PDT)
x-topics: [EE]
x-mime-autoconverted: from Quoted-printable to 8bit by PCH.mit.edu id
	17CNJwnM024012
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

Hi Neil,

Yes, the voltage seen by the PTC is the product of current and resistance, =
so you=20
are correct: in normal operation the voltage drop is minimal. You will of c=
ourse=20
remember what follows, apologies in advance :-) If/when the fuse "trips" it=
's=20
resistance goes up, voltage accross it goes up, maintaining enough V x I =
=3D P to=20
keep the PTC warm enough to stay in it's tripped state. Then when the suppl=
y or=20
fault is removed it cools and "resets", resistance drops back to normal low=
 state.=20
PTC voltage rating generally needs to match or exceed the supply voltage.

Hope this helps~!

On 12 Aug 2021 at 18:22, Neil wrote:

> What exactly is the voltage rating of a PTC fuse?=A0 ( I was selecting on=
e=20
> today and it dawned on me that I never really paid attention to this. )
> As I see it, it has to be the voltage across the fuse, and that's based=20
> on it's internal resistance the current through it.
> At no point can I see a higher voltage getting across the fuse, so if I=20
> use it in a circuit that runs at a higher voltage (say a basic PS, fan,=20
> switch), that should be fine, correct?


--=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
.