Post by thread:DCC vs Darlington Transistor

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 {Quote hidden}> > 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 <spam_OUTdwaynerTakeThisOuTplanet.eon.net> > > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > > (403) 489-3199 voice (403) 487-6397 fax > >

Thomas McGahee wrote: > 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). I'm not sure it was the *input* bias (effective Vbe) that was concerning the original poster. More likely the effective Vcesat, which is identical to a darlington and consists of the Vcesat of the input transistor *plus* the Vbe of the second. > A DCC has gain = Beta1*Beta2. Virtually identical to a darlington of course, where it is Beta1*(Beta2+1). -- Cheers, Paul B.

This is very useful. I once used five transistors in a serial connection like this. I could almost read my thoughts. Had to use implement b-e resistors to keep it off. Has also slow turnoff without them. The LP324 OpAmp i think i remember has a smart connection of three transistors that first work like this, then when PNP saturated, if sufficiently low collector current, there was anither NPN that could achieve a effective saturation under 0,1V or something. Anybody know how that trick is done? /Morgan At 09:41 1998-07-26 -0400, you wrote: {Quote hidden}>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 {Quote hidden}>> > parts are fine. North American part numbers preferred. Any thoughts? >> > >> > Thanks! >> > >> > dwayne >> > >> > >> > Dwayne Reid <.....dwaynerKILLspam@spam@planet.eon.net> >> > Trinity Electronics Systems Ltd Edmonton, AB, CANADA >> > (403) 489-3199 voice (403) 487-6397 fax >> > > > / Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \ \ mrtKILLspaminame.com, ph: +46 (0)414 70741; fax +46 (0)414 70331 /

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: {Quote hidden}>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 <.....dwaynerKILLspam.....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...

On Tue, 28 Jul 1998, Tom Handley wrote: > 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. Well, since we're at it, have you considered a MOSFET with a Resistor (and maybe a diode or two) in parallel with Gate and Source ? Because this will do precisely what you are after, and outperform both the Darlington and the other configuration in the process, and may be cheaper on account of the lower part number used. regards, Peter

Peter, I was just commenting on Tom's circuit which is something I had not considered in a long time. In my own work, I normally use MOSFETs. Actually, I have'nt used discrete bipolar transistors in a long time other than IGBTs. His comment triggered a `rusty old brain path' that said; "Oh yeah, I forgot about that" ;-) - Tom At 06:53 PM 7/28/98 +0000, Peter L. Peres wrote: {Quote hidden}>On Tue, 28 Jul 1998, Tom Handley wrote: > >> 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. > >Well, since we're at it, have you considered a MOSFET with a Resistor (and >maybe a diode or two) in parallel with Gate and Source ? Because this will >do precisely what you are after, and outperform both the Darlington and >the other configuration in the process, and may be cheaper on account of >the lower part number used. > >regards, > > Peter > >