# [sdiy] Measuring Rbe

sdiy sdiy at haraldswerk.de
Wed Jun 15 11:46:34 CEST 2011

```Thank you Ian,

for calculation: I calculate the delta of Vce and Ib from point to point
(measured in 1k steps). Dividing the deltas give me the Rbe. Then i sum the
Rbe up and divide through the numbers of measuring points to become the
average. Right?

HA

Am Mittwoch, 8. Juni 2011, 19:19:41 schrieben Sie:
> At 10:14 AM 6/8/2011, sdiy wrote:
> >I followed the description above. Emitter on ground. Basis at +10V with
> >varying the R in one k steps from 1k to 30k. Collector open. Then
> >calculating deltaVce / deltaIb to become Rbe
> >Measuring an CA3046 at 26degCelsius I calculated Rbe at about 7Ohm. That
> >is near what Rene measured.
> >I will give the other figures i did when the method is confirmed.
> >
> >But i am not sure if i understand it right. I am wondering why i can
> >measure Vce when the collctor is open? Can anyone shet some light on
> >this?
>
> The procedure is correct, I believe.  Both Rene and I did a number of
> devices this way a "few" years ago.
>
> To measure the extra series resistance Rbe, you want to measure Vce vs Ie
> and calculate the slope at high current, where the slope is dominated by
> Rbe.  The measurement needs to be done at zero collector current so that
> any spurious resistance Rcb does not contribute. Ie is the same as the base
> current Ib, because the collector is open. So the slope of Vce vs Ib gives
> you the desired result.  Seems a bit odd, but I think the way to look at it
> is simply that the collector floats to whatever voltage is necessary to
> satisfy the transistor characteristics at zero collector current.
>
>    Ian

```