reg + reference
in [Design]
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From: John Larkin on 26 Mar 2010 13:19 ftp://jjlarkin.lmi.net/V220_reg.JPG John
From: Jim Thompson on 26 Mar 2010 13:37 On Fri, 26 Mar 2010 10:19:55 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >ftp://jjlarkin.lmi.net/V220_reg.JPG > > >John Man! High class engineering :-) ...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 | The only thing bipartisan in this country is hypocrisy
From: Jan Panteltje on 26 Mar 2010 15:21 On a sunny day (Fri, 26 Mar 2010 10:19:55 -0700) it happened John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in <13rpq5lqd1lj1k9flb9orfr2vcl2tuucpi(a)4ax.com>: > >ftp://jjlarkin.lmi.net/V220_reg.JPG > > >John > No money for a real current source or current mirror? Does that 1M depending on beta circuit change a lot over temperature? Its Vbe will change, so will the Ib.
From: Artemus on 26 Mar 2010 17:43 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:13rpq5lqd1lj1k9flb9orfr2vcl2tuucpi(a)4ax.com... > > ftp://jjlarkin.lmi.net/V220_reg.JPG > > > John > How much current can that 1117 source from it's ADJ pin? Art
From: John Larkin on 26 Mar 2010 17:24
On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Fri, 26 Mar 2010 10:19:55 -0700) it happened John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in ><13rpq5lqd1lj1k9flb9orfr2vcl2tuucpi(a)4ax.com>: > >> >>ftp://jjlarkin.lmi.net/V220_reg.JPG >> >> >>John >> > >No money for a real current source or current mirror? >Does that 1M depending on beta circuit change a lot over temperature? >Its Vbe will change, so will the Ib. The current into the reference will be more constant than if I just used a resistor with a nominal 0.3 volt drop across it. The BCX71K has a very tight beta spec. It would probably be better than using the current mirror discussed in another thread recently. And we have BCX71Ks in stock for under 4 cents each. The +15 is not very well regulated, and I'm tight for space. I guess I could use a depletion mode fet from +15. That's just one part. The current regulation would be fair, but I wouldn't have any flexibility on setting current. An LND150 is 33 cents, no problem there, but Idss is 1 to 3 mA and it may change a bunch with temperature. Or maybe there exists a 3 volt 3-wire reference that would work from 3.3 volts. This will be the ADC voltage reference for an NXP ARM processor. I'm doing a 12-channel 4-20 mA thing, electrically isolated per channel, with an ARM per channel. The ARM and other stuff might need 45 mA or so, less if we can sleep the code a lot. Or I could use a very good regulator to make 3.3 and run everything off that, Vref included. More parts. Or add another regulator, 15-to-5 and derive the Vref from the +5. Or find a good 3-volt reference that works directly from +15. I figured using the beta thing would predictably get the geezers all worked up. There's nothing wrong with it. John |