Alt-BEAM Archive
Message #05030
To: beam@sgiblab.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Mon, 5 Jul 1999 10:56:50 +0200 (CEST)
Subject: [alt-beam] Re: hFE (was: PLEASEEEEEEEEEEEEEE< Dumb Questions >)
On Sun, 4 Jul 1999, Ian Bernstein wrote:
> > What is the transistor hFE thingy for
> Testing transistors and finding the hFE of them.
The hFE being the DC current gain. Note that the hFE will reach a
best value at a certain collector current, which depends on the
type of transistor; for a 2N3904 or 2N3906 it may for instance be
specified at 2mA, while for a BC337 it will be tabled at 100mA.
That's one reason for using a BC337 (or 2N2219, 2N2222) to drive
your motors, instead of a 3904. The other is VCEsat, the voltage
left over collector and emitter when the transistor is saturated
(fully switched on). A BC337 will reach a lower VCEsat at less base
current than a 3904, at the collector current demanded by for
instance a pager motor.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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