From: Fred Bloggs
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Subject: Re: Transistor current gain with temperature
References: <3D944E62.AE8D71CC@hotmail.com> <3D94633C.363EC763@kth.se>
Date: Sat, 28 Sep 2002 17:03:51 GMT
NNTP-Posting-Date: Sat, 28 Sep 2002 10:03:51 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Jim Thompson wrote:
> On Fri, 27 Sep 2002 15:55:08 +0200,
> Uwe Zimmermann ,
> In Newsgroup: sci.electronics.design,
> Article: <3D94633C.363EC763@kth.se>,
> Entitled: "Re: Transistor current gain with temperature",
> Wrote the following:
> |Tom Sharp wrote:
> |> Does anyone know the minimum current gain of a BC817-16 @ -40 degrees C
> |> with 1mA collector current?
> |Transistor gain is higher at lower temperatures, however, -40C shouldn't
> |have a too strong influence. Therefore I would assume the minimum
> |current gain to be only slightly above the minimum current gain at room
> |According to the datasheet of the BC817-16 at onsemi.com, the current
> |gain at Ic=1mA is about a factor 3 below the value at Ic=100mA stated as
> |Alltogether I would strongly expect the minimum current gain at 1mA and
> |-40C not to be below 30.
> | Uwe.
> Wrong! BIPOLAR Gain is lower at low temperatures and higher at high
> temperatures. A loose rule of thumb I use when designing I/C's is
> that gain (beta) at -55°C is 1/2 of the gain at 27°, and the gain at
> 125°C is twice that at 27°C.
This was my understanding also, the beta variation is roughly +1%/oC
over reasonable temperature excursions about 25oC.