Maintaining a Vbe Multiplier's bias value
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From: Tim Williams on 11 Feb 2010 11:08 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in message news:r358n59g5vkv4brn2vc795lhoineb2jvhd(a)4ax.com... > And a 2.5V "dead-band", but it _is_ precisely known, and temperature > stable. Interesting thought if you have high enough power supplies. Bonus: the dead band allows you to use that TL431 "Vbe" mentinoed earlier. Too bad they're so slow (hardly capable for audio). Does anyone make "fast" regulators (without being stupid LDOs)? Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jon Kirwan on 11 Feb 2010 12:53 On Thu, 11 Feb 2010 07:34:40 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 11 Feb 2010 01:07:52 -0800, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >>On Wed, 10 Feb 2010 23:24:04 -0700, "bg" <bg(a)nospam.com> >>wrote: >> >>>This is the model that came with circuitmaker - - >>>*2N3904 >>>*Si 310mW 40V 200mA 300MHz pkg:TO-92B 1,2,3 >>>.MODEL 2N3904 NPN(IS=1.4E-14 BF=300 VAF=100 IKF=0.025 ISE=3E-13 >>>+ BR=7.5 RC=2.4 CJE=4.5E-12 TF=4E-10 CJC=3.5E-12 TR=2.1E-8 XTB=1.5 >>>KF=9E-16 ) >> >>Thanks!! LTspice's model is: >> >>.model 2N3904 NPN(IS=1E-14 VAF=100 Bf=300 IKF=0.4 XTB=1.5 >>+ BR=4 CJC=4E-12 CJE=8E-12 RB=20 RC=0.1 RE=0.1 TR=250E-9 >>+ TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40 Icrating=200m >>+ mfg=Philips) >> >><snip> >> >>.MODEL 2N3904 NPN( >>+IS=1.26532e-10 BF=206.302 NF=1.5 VAF=1000 >>+IKF=0.0272221 ISE=2.30771e-09 NE=3.31052 BR=20.6302 >>+NR=2.89609 VAR=9.39809 IKR=0.272221 ISC=2.30771e-09 >>+NC=1.9876 RB=5.8376 IRB=50.3624 RBM=0.634251 >>+RE=0.0001 RC=2.65711 XTB=0.1 XTI=1 >>+EG=1.05 CJE=4.64214e-12 VJE=0.4 MJE=0.256227 >>+TF=4.19578e-10 XTF=0.906167 VTF=8.75418 ITF=0.0105823 >>+CJC=3.76961e-12 VJC=0.4 MJC=0.238109 XCJC=0.8 >>+FC=0.512134 CJS=0 VJS=0.75 MJS=0.5 >>+TR=6.82023e-08 PTF=0 KF=0 AF=1) > >Go with the OnSemi model. > > ...Jim Thompson Instead of a blanket Is and BF, or a VA set at a default 100, and Ise seems more realistically close to Is... Well, it appears that it was actually a developed model done by measuring (and with Is, likely extrapolated from measurements) and deals with the high level injection knee. It looks solid and actually uses something other than the default value for Eg, which is taken as 1.11 in LTspice. I cannot recall ever getting a beta near 300 with one, either. What I completely lack is an understanding of the processes used to make these and how those processes vary between alternate manufacturers and which parameters are likely to be very similar between them and which may be quite different for the same part designation. In other words, although OnSemi has a realistic model for their own parts, which is fine for simulating their parts more accurately -- is there a reason to shop around and actually _select_ someone else's parts for some application reason. And in what cases would you not bother wasting time shopping around and for what other cases would you decide to spend the time, because you know enough about how they are made and what differences that can make to be worth that effort to test and verify when making a selection? Jon
From: Jon Kirwan on 11 Feb 2010 13:03 On Thu, 11 Feb 2010 09:53:37 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: ><snip> >In other words, although OnSemi has a realistic model for >their own parts, which is fine for simulating their parts >more accurately -- is there a reason to shop around and >actually _select_ someone else's parts for some application >reason. And in what cases would you not bother wasting time >shopping around and for what other cases would you decide to >spend the time, because you know enough about how they are >made and what differences that can make to be worth that >effort to test and verify when making a selection? To further clarify this question, I already know that some manufacturers provide 2N2222A's with 40V and with 60V max Vce specifications. I assume this is a function of differences in the FAB processes they choose to apply in making their parts. That's what I'm talking about... not only for differences in model parameters but _useful_ differences, too. And how do I learn the salient details of various FAB processes? Thanks, Jon
From: John Larkin on 11 Feb 2010 13:14 On Thu, 11 Feb 2010 10:08:38 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >message news:r358n59g5vkv4brn2vc795lhoineb2jvhd(a)4ax.com... >> And a 2.5V "dead-band", but it _is_ precisely known, and temperature >> stable. Interesting thought if you have high enough power supplies. > >Bonus: the dead band allows you to use that TL431 "Vbe" mentinoed earlier. > >Too bad they're so slow (hardly capable for audio). Does anyone make "fast" >regulators (without being stupid LDOs)? > >Tim If you drive both adjust pins with the signal input, the 317 output is Vin+1.25 and the 337 output is Vin-1.25. Connect them to the output through a couple of resistors, valued to set the idle current. Where's the deadband? Or you can take the output from the 317 output pin, with the 337 now acting like a constant-current sink to the 317. I like to use LM1117s as power emitter followers, inside the loop of an opamp. That makes a cheap, well protected power driver, for load cell excitation and such. I did a bunch of tests to see whether flailing the adj pin can damage the regulator, and never managed to break one. John
From: Jim Thompson on 11 Feb 2010 13:50
On Thu, 11 Feb 2010 10:03:16 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Thu, 11 Feb 2010 09:53:37 -0800, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >><snip> >>In other words, although OnSemi has a realistic model for >>their own parts, which is fine for simulating their parts >>more accurately -- is there a reason to shop around and >>actually _select_ someone else's parts for some application >>reason. And in what cases would you not bother wasting time >>shopping around and for what other cases would you decide to >>spend the time, because you know enough about how they are >>made and what differences that can make to be worth that >>effort to test and verify when making a selection? > >To further clarify this question, I already know that some >manufacturers provide 2N2222A's with 40V and with 60V max Vce >specifications. I assume this is a function of differences >in the FAB processes they choose to apply in making their >parts. That's what I'm talking about... not only for >differences in model parameters but _useful_ differences, >too. > >And how do I learn the salient details of various FAB >processes? > >Thanks, >Jon Once upon a time there was JEDEC, and all 2N2222A's had to be the same in regards to essential specifications. But I'd use the OnSemi model, irrespective... the LTspice version lets too many variables drop back to their default values... might not matter, but who knows. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |