Tom, thanks for posting this. While I take this for granted in ICs I
have'nt considered this circuit in a long time. I was also thinking
Darlington. I had earlier made a comment about how many questions asked
in this group force us to visit subjects we have'nt looked at in a long
time and this is a good example.

   - Tom

At 09:41 AM 7/26/98 -0400, Tom McGahee wrote:
>Dwayne,
>Have you considered using a Direct Coupled Compound (DCC) arrangement? This
>has the gain advantage of a Darlington, but has only one forward
>diode drop (Vbe drop). A DCC has gain = Beta1*Beta2. The 'device' has the
>characteristics of the input transistor. A disgusting ascii drawing follows.
>
>*****************************************************
>Direct Coupled Compound (DCC). "NPN" Equivalent Shown.
>One Vbe forward diode drop. Gain=Gain_npn*Gain_pnp
>
>             Effective Collector
>                      |
>                      |
>                 PNP  V (E)
>                    |/
>              ------|
>        NPN |/      |\
>Base--------|         | (C)
>            |\        |
>              V       |
>              |       |
>              --------*
>                      |
>                      |
>               Effective Emitter
>
>*******************************************************
>Add this to your 'collection'.
>
>Hope this helps.
>Fr. Tom McGahee
>
>>
>> > Hi!
>> >
>> > I'm looking for recomendations for TO-220 NPN and PNP transistors that have
>> > moderate current gains at about 1 Amp.  Should be good for at least 40V,
>hfe
>> > greater than 100, reasonably robust.  My old standbys TIP31, TIP32, TIP41,
>> > TIP42 don't have enough gain and the TIP120 - TIP127 are darlingtons and
>> > have too much voltage drop.  I don't need complimentary pairs so unmatched
>> > parts are fine.  North American part numbers preferred.  Any thoughts?
>> >
>> > Thanks!
>> >
>> > dwayne
>> >
>> >
>> > Dwayne Reid   <dwayner@planet.eon.net>
>> > Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
>> > (403) 489-3199 voice     (403) 487-6397 fax
>> >
>
>
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs...