Re: Q: feedback and input impedance in a emitter follower

On Thu, 26 Oct 2006 11:10:09 +0100, Eeyore
<rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:



The Phantom wrote:

On Thu, 26 Oct 2006 07:55:47 +0100, Eeyore
<rabbitsfriendsandrelations@xxxxxxxxxxx> wrote:

The trick is to design parameter sensitivity out as far as possible.

A worthy goal. To know when the goal has been reached, you must have a
method of determining what the parameter sensitivities are. Will you share
your method of doing this?

I'll analyse the circuit for you if you like.

Initially without feedback

First off I want to know the hfe for the BC547A. Interesting since Philips doesn't list a
BC547A so I'l use the BC547B !

200 min 290 typ 400 max @ 2mA which is close enough to our needs.

Note that the other h parameters you want aren't listed - nor have I ever seen them in any
data***.

They're in the Vishay data *** available at:
http://www.datasheetcatalog.com/datasheets_pdf/B/C/5/4/BC547A.shtml

Figure 8 in that data *** shows how they vary with collector current.

That is *very* unusual / untypical however.

I've never seen any semi maker quote these before.

Look in the big brown Motorola "Small-Signal Transistor Data" book.

The venerable 2N2222, the 2N3903 family and others have h parameters. A
number of the higher frequency devices have admittance parameters.

The National Semiconductor data book gives h parameters for the 2N2907,
2N3019, 2N3904, 2N5086, and 2N5088.

The Fairchild Semiconductor data book gives h parameters for the 2N2695,
2N3072, 2N3120, 2N3502, 2N3930 and quite a few more.

My old General Electric data book gives h parameters for the 2N43
(germanium), 2N461, 2N524, 2N4424, 2N3858, 2N5232, 2N3392, 2N5827 and LOTS
more.

I can't speak for the European manufacturers, but here in the states it's
fairly common.


Graham

.

Quantcast