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From: email@example.com (Bob Wilson)
Subject: Re: LM317 or 7808 is better performance for 9V output ?
Date: Tue, 10 Dec 2002 03:34:24 -0000
Organization: Your Organization
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References: <3DEDABCA.906FB592@fanwap.com> <firstname.lastname@example.org> <email@example.com>
In article <firstname.lastname@example.org>,
>"Trevor Wilson" wrote in message
>> "Tong Narak" wrote in message
>> > Hi all,
>> > A. LM317 require 5V head room.
>> > B. 78XX require 2V head room ( Is these correct ? ).
>> > I would like to set the output to 9V. Load ~300mA.
>> > (1) Which one is better proformance and efficiency ?
>> > (2) 7805 and 7808 are same efficiency when adjustable to 9V ?
>> **The LM317 is a superior performer, both in regulation and noise.
>I think you will find that the 78xx has better specs (according to my
>data sheets). I think you may also find that 317's performance would
>degrade even further due to the use of external components if not
>designed correctly. Besides, if you were really concerned with
>regulation and noise at those levels you wouldn't be using a three
>terminal regulator anyway.
Noise especially. 3-terminal regulators will do nothing to clean up noise.
Their internal error amp bandwidth is dead slow; nowhere near fast enough to
clean up noise. It is the caps that are typically added at their output that
can reduce noise. The regulators themselves contribute nothing.
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