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From: Victor Roberts
Organization: Roberts Research & Consulting, Inc.
X-Mailer: Mozilla 4.78 [en] (Win98; U)
Subject: Re: luxeon star leds
References: <3DDD9A57.58900EFB@RobertsResearchInc.com> <email@example.com> <3DDDB646.96D0D9D2@RobertsResearchInc.com>
Date: Fri, 22 Nov 2002 18:07:32 GMT
NNTP-Posting-Date: Fri, 22 Nov 2002 10:07:32 PST
Lizard Blizzard wrote:
> Victor Roberts wrote:
> > John Larkin wrote:
> >>On Fri, 22 Nov 2002 02:45:37 GMT, Victor Roberts
> >> wrote:
> >>>The thermal resistance to
> >>>"free space" of an unmounted device should therefore be
> >>>lower than the thermal resistance of a device mounted to a
> >>>heat sink.
> >>Then why do people buy heat sinks?
> > Because use of heat sinks will lower the temperature of the
> > junction. Operating without a heat sink will decrease the
> > apparent thermal resistance between the junction and the
> > heat sink mounting plate on the LED because of the other
> > paths available for power loss. Operating without a heat
> > sink does not lower the junction temperature, it raises it.
> What you really meant is that operating without a heatsink decreases the
> thermal conductance, which is the inverse of thermal resistance.
No, I mean what I said in my last message. Operating with a
heat sink _decreases_ the "apparent" thermal resistance
between the junction of the LED (or any other semiconductor
device) and the heat sink mounting plate on the LED (or
other semiconductor) package.
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