Re: Query - How valves and transistors work - Article 15444 - go-pugleaf

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Article #15444

Re: Query - How valves and transistors work

#15444

From: Duncan Barclay
Date: Tue, 29 Dec 1998 00:00

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In article <76b08g$jo4$1@news-1.news.gte.net>,
	Doug <do@not.spam> writes:
> Nightjar wrote:
>> 
>> Could anybody out there tell me how valves and transistors work, please? I
>> would be eternally grateful.
> 
> In a couple of sentences or less?  
> 
> Valves are voltage devices.  You can control a relatively 
> large voltage with a small amount of voltage. 
> 
> Transistors are current devices.  You can control a relatively 
> large current with a small amount of current. 
> 

Sorry, you are wrong twice. Both valves and transistors (BJTs and FETs)
are voltage controlled current sources.

Valves look like vcvs because they usually are used with small currents
and large impedances.

Transistors can look like cccs because they are often used to switch currents
in low impedance circuits. The base current is essentially a parasitic,
but fundimental to BJT operation. It is possible to get very high beta
BJTs by bandgap engineering (hetero-junctions at the base-emitter
interfaces).

Duncan

-- 
________________________________________________________________________
Duncan Barclay          | God smiles upon the little children,
dmlb@ragnet.demon.co.uk | the alcoholics, and the permanently stoned.
________________________________________________________________________

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From: dmlb@ragnet.demon.co.uk (Duncan Barclay)
Subject: Re: Query - How valves and transistors work
Date: 1998/12/29
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