Op Amp Calculations
in [Design]
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From: Terry Given on 6 Oct 2005 15:59 Winfield Hill wrote: > Rich Grise wrote... > >>Dibs on a half share of ROFLMAOPIMP! > > > PIMP? > > Pee In My Pants.... Cheers Terry
From: Terry Given on 6 Oct 2005 16:01 Jim Thompson wrote: > On Thu, 06 Oct 2005 15:39:08 GMT, Fred Bloggs <nospam(a)nospam.com> > wrote: > > >> >>Jim Thompson wrote: >> >>>On Thu, 06 Oct 2005 17:45:05 +1300, Terry Given <my_name(a)ieee.org> >>>wrote: >>> >>> >>> >>>>Jim Thompson wrote: >>>> >>>> >>>>>On Wed, 05 Oct 2005 13:03:55 GMT, Fred Bloggs <nospam(a)nospam.com> >>>>>wrote: >>>>> >>>>> >>>>>>Fred Bartoli wrote: >>>>>> >>>>>> >>>>>>>"Terry Given" <my_name(a)ieee.org> a ?crit dans le message de >>>>>>>news:1128463369.256572(a)ftpsrv1... >>>>>>> >>>>>>> >>>>>>>>Fred Bloggs wrote: >>>>>>>> >>>>>>>> >>>>>>>>>Terry Given wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>>>What about the typo? the 2nd transistor shorts out the +5V supply.... >>>>>>>>> >>>>>>>>shouldnt there be something to limit current though? +5V...Vce...Vbe >>>>>>>>with nary a resistor in sight. ultimately the base current could be as >>>>>>>>high as the opamp output current (assuming negligible contribution from >>>>>>>>the summing junction).... >>>>>>> >>>[snip] >>> >>> >>>>>>Not quite, essentially all the incremental base drive voltage is >>>>>>developed across hie of the first transistor. Your reasoning is wrong >>>>>>and your estimate is high. >>>>> >>>"hie"... what BS! Fred must be of the "Kevin School" of transistor >>>operation ;-) >>> >>> >>> >>>>>And it STILL will go up in flames during power-up. Sheeesh! Such >>>>>DESIGN ;-) >>>>> >>>>>[snip] >>>>> >>>>> ...Jim Thompson >>>> >>>>Hi Jim, >>>> >>>>can you please elaborate on why? I presume because of the 2nd transistor.... >>>> >>>>Cheers >>>>Terry >>> >>> >>>No limit on IB of 1st transistor except output capability of OpAmp >>> >>>IC of 1st transistor IS limited somewhat by FB resistors, but >>>substantial IB is introduced into 2nd transistor >>> >>>Absolutely nothing to limit IC of 2nd transistor except current >>>crowding >>> >>>My best guess is that all three transistors will flame or be seriously >>>damaged when Murphy chooses ;-) >>> >>>(And the bandwidth will be nothing like claimed.) >>> >>>What was the original intent (OP)? I didn't get in on this thread at >>>the beginning. >>> >>> ...Jim Thompson >> >>This is not rocket science- we already said that the second transistor C >>should be tied to the CE collector. If you're worried by the OA dumping >>excessive current into the base then put a 560 in series with its output. > > > That's still insufficient. Good engineering practice would limit base > drive from the OpAmp AND also the collector current of the 2nd > transistor. > > ...Jim Thompson Thanks Jim, thats pretty much what I figured. Its like driving, really. any fool can drive on a straight, flat road with no traffic and good visibility. Going round a corner sideways in the pouring rain, with a logging truck coming towards you, sorts the men from the boys. Cheers Terry
From: Jim Thompson on 6 Oct 2005 16:08 On Fri, 07 Oct 2005 09:01:41 +1300, Terry Given <my_name(a)ieee.org> wrote: >Jim Thompson wrote: >> On Thu, 06 Oct 2005 15:39:08 GMT, Fred Bloggs <nospam(a)nospam.com> >> wrote: [snip] >> >> That's still insufficient. Good engineering practice would limit base >> drive from the OpAmp AND also the collector current of the 2nd >> transistor. >> >> ...Jim Thompson > >Thanks Jim, thats pretty much what I figured. Its like driving, really. >any fool can drive on a straight, flat road with no traffic and good >visibility. Going round a corner sideways in the pouring rain, with a >logging truck coming towards you, sorts the men from the boys. > >Cheers >Terry I did that once on snow. Nothing like sliding sideways, down a hill yet, and dodging traffic, to put some "age" on you ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Rich Grise on 7 Oct 2005 14:07 On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote: > On Fri, 07 Oct 2005 09:01:41 +1300, Terry Given <my_name(a)ieee.org> > wrote: > >>Jim Thompson wrote: >>> On Thu, 06 Oct 2005 15:39:08 GMT, Fred Bloggs <nospam(a)nospam.com> >>> wrote: > [snip] >>> >>> That's still insufficient. Good engineering practice would limit base >>> drive from the OpAmp AND also the collector current of the 2nd >>> transistor. >>> >>> ...Jim Thompson >> >>Thanks Jim, thats pretty much what I figured. Its like driving, really. >>any fool can drive on a straight, flat road with no traffic and good >>visibility. Going round a corner sideways in the pouring rain, with a >>logging truck coming towards you, sorts the men from the boys. >> >>Cheers >>Terry > > I did that once on snow. Nothing like sliding sideways, down a hill > yet, and dodging traffic, to put some "age" on you ;-) > Ever tried fishtailing on the freeway at 55MPH on black ice? That's kind of a rush too. ;-) Cheers! Rich
From: Jim Thompson on 7 Oct 2005 14:28
On Fri, 07 Oct 2005 18:07:00 GMT, Rich Grise <rich(a)example.net> wrote: >On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote: > >> On Fri, 07 Oct 2005 09:01:41 +1300, Terry Given <my_name(a)ieee.org> >> wrote: >> >>>Jim Thompson wrote: >>>> On Thu, 06 Oct 2005 15:39:08 GMT, Fred Bloggs <nospam(a)nospam.com> >>>> wrote: >> [snip] >>>> >>>> That's still insufficient. Good engineering practice would limit base >>>> drive from the OpAmp AND also the collector current of the 2nd >>>> transistor. >>>> >>>> ...Jim Thompson >>> >>>Thanks Jim, thats pretty much what I figured. Its like driving, really. >>>any fool can drive on a straight, flat road with no traffic and good >>>visibility. Going round a corner sideways in the pouring rain, with a >>>logging truck coming towards you, sorts the men from the boys. >>> >>>Cheers >>>Terry >> >> I did that once on snow. Nothing like sliding sideways, down a hill >> yet, and dodging traffic, to put some "age" on you ;-) >> >Ever tried fishtailing on the freeway at 55MPH on black ice? That's >kind of a rush too. ;-) > >Cheers! >Rich > I drove the Pennsylvania Turnpike from west-end-to-east-end one time with an eery feeling of never quite touching the ground ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |