Forums

Current source circuit fail.

Started by George Herold November 14, 2017
On Wednesday, November 15, 2017 at 1:06:28 PM UTC-5, Jim Thompson wrote:
> On Wed, 15 Nov 2017 08:15:02 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > > [snip] > > > >gnd---RR---+--RR--+ > > ||\ | > > +|-\ | > > Ina134 | >--+-(A)-Rset-+---output to gnd. > > +|+/ | > > ||/ /| | > > Vin--RR--+----RR---< +-----+ > > \| > > Buffer opa134 > > > >I moved my (A) power opamp. Though the opa544 doesn't seem to like > >having it's output driven near the negative rail. > >https://www.dropbox.com/s/c4qmibb7gcfv0mb/VCCS.BMP?dl=0 > > > >Chan. 1 is voltage across 200 ohm resistor, chan 2. is input. > >(100 ohm 'set' resistor. 1 V_in= 10mA > > > > > >George H. > >> > > Why all that complexity? Plus the load behavior is inside your loop. > A dual R-R OpAmp plus either a PMOS or PNP for the high current will > easily solve your problem... and be stable.
Hmm well doesn't look all that complex to me. It started as a current source, bipolar with grounded load. Without the power opamp. The int-amp->R-> opamp circuit is cute I thought. Then I was wondering about more current. (It sometimes would be nice to drive something like magnet coils at ~1A on each side of zero... I don't need a grounded load for that, and could just use the power opamp in the typical V to I converter. Sense R to ground.... but I've done variations on that circuit a million times. (OK maybe ten times. :^) Anyway mostly playing around. George H.
> > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > To save time, Let's just assume I know everything.
On Wed, 15 Nov 2017 11:06:16 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Wed, 15 Nov 2017 08:15:02 -0800 (PST), George Herold ><gherold@teachspin.com> wrote: > >[snip] >> >>gnd---RR---+--RR--+ >> ||\ | >> +|-\ | >> Ina134 | >--+-(A)-Rset-+---output to gnd. >> +|+/ | >> ||/ /| | >> Vin--RR--+----RR---< +-----+ >> \| >> Buffer opa134 >> >>I moved my (A) power opamp. Though the opa544 doesn't seem to like >>having it's output driven near the negative rail. >>https://www.dropbox.com/s/c4qmibb7gcfv0mb/VCCS.BMP?dl=0 >> >>Chan. 1 is voltage across 200 ohm resistor, chan 2. is input. >>(100 ohm 'set' resistor. 1 V_in= 10mA >> >> >>George H. >>> > >Why all that complexity? Plus the load behavior is inside your loop. >A dual R-R OpAmp plus either a PMOS or PNP for the high current will >easily solve your problem... and be stable. > > ...Jim Thompson
How would that work? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Wed, 15 Nov 2017 11:09:21 -0800, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Wed, 15 Nov 2017 11:06:16 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >
[snip]
>> >>Why all that complexity? Plus the load behavior is inside your loop. >>A dual R-R OpAmp plus either a PMOS or PNP for the high current will >>easily solve your problem... and be stable. >> >> ...Jim Thompson > >How would that work?
See "CurrentSourceConceptual.pdf" on the S.E.D/Schematics Page of my website for a bidirectional source/sink version. Simplification to single-sided is left as an exercise for the student ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | To save time, Let's just assume I know everything.
George Herold <gherold@teachspin.com> wrote:

> I made this nice VCCS from a differential amp (Ina134), > resistor and opamp (opa134) feedback. It was good to > 40 or 50 mA. Bad ass-ci.
> gnd---RR---+--RR-----+ > ||\ | > +|-\ | > Ina134 | >-(A)-+--Rset-+---output to gnd. > +|+/ | > ||/ /| | > Vin--RR--+----RR---< +-----+ > \| > Buffer opa134 > It's in AoE3. > Rset sets the current/voltage ratio and the other R's are > in the ina134. > I was thinking about more current and added a power opamp > in the (A) spot. Didn't work, the power opamp OPA544 railed > at the wrong side.. or something. The ina134 spec sheet > shows a fast buffer BUF634? Would that be better. > (maybe I need to limit the voltage to the ina134?)
> This bipolar current source has nice return to ground. > It's got an output impedance of Rset. (less nice.)
> George H.
Here are two simpler ones that might interest you. Simple bipolar current source The first one is useful if you can lift the ground and insert a current sense resistor. It takes a fairly wideband op amp to get to 1MHz. I have set the values to deliver +/- 100 mA to a load of zero to 125 ohms. Modified Howland Current Pump The second one delivers +/- 500 mA to a grounded load. I did not mess with getting it to run at 1 MHz, but the same techniques used in the first version should work as well. Both circuits use a single op amp so there should be no problems with feedback oscillations due to different GBW products. https://silvercell.000webhostapp.com/sed/4B6F8609.ZIP
On Wednesday, November 15, 2017 at 5:01:29 PM UTC-5, Steve Wilson wrote:
> George Herold <gherold@teachspin.com> wrote: > > > I made this nice VCCS from a differential amp (Ina134), > > resistor and opamp (opa134) feedback. It was good to > > 40 or 50 mA. Bad ass-ci. > > > gnd---RR---+--RR-----+ > > ||\ | > > +|-\ | > > Ina134 | >-(A)-+--Rset-+---output to gnd. > > +|+/ | > > ||/ /| | > > Vin--RR--+----RR---< +-----+ > > \| > > Buffer opa134 > > It's in AoE3. > > Rset sets the current/voltage ratio and the other R's are > > in the ina134. > > I was thinking about more current and added a power opamp > > in the (A) spot. Didn't work, the power opamp OPA544 railed > > at the wrong side.. or something. The ina134 spec sheet > > shows a fast buffer BUF634? Would that be better. > > (maybe I need to limit the voltage to the ina134?) > > > This bipolar current source has nice return to ground. > > It's got an output impedance of Rset. (less nice.) > > > George H. > > Here are two simpler ones that might interest you. > > Simple bipolar current source > > The first one is useful if you can lift the ground and insert a current > sense resistor. It takes a fairly wideband op amp to get to 1MHz. I have > set the values to deliver +/- 100 mA to a load of zero to 125 ohms. > > Modified Howland Current Pump > > The second one delivers +/- 500 mA to a grounded load. I did not mess with > getting it to run at 1 MHz, but the same techniques used in the first > version should work as well. > > Both circuits use a single op amp so there should be no problems with > feedback oscillations due to different GBW products. > > https://silvercell.000webhostapp.com/sed/4B6F8609.ZIP
Thanks, I don't care all that much about HF in my current sources, at least at the moment. At high current it's coils, lower current is some 'resistive' sensor of unknown impedance (I guess a diode might be common.) But it'll be down the bottom of a probe or on the end of coax and have ~100 pF of C. (100 pF x 10 k ohm life slows down. :^) George H. (and sure there's tricks for input C.) Steve, I didn't look at your circuits/links.. at home and slow, I'll check 'em out tomorrow.)
On Wed, 15 Nov 2017 13:28:36 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Wed, 15 Nov 2017 11:09:21 -0800, John Larkin ><jjlarkin@highland_snip_technology.com> wrote: > >>On Wed, 15 Nov 2017 11:06:16 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >[snip] >>> >>>Why all that complexity? Plus the load behavior is inside your loop. >>>A dual R-R OpAmp plus either a PMOS or PNP for the high current will >>>easily solve your problem... and be stable. >>> >>> ...Jim Thompson >> >>How would that work? > >See "CurrentSourceConceptual.pdf" on the S.E.D/Schematics Page of my >website for a bidirectional source/sink version. Simplification to >single-sided is left as an exercise for the student ;-) > > ...Jim Thompson
Here's an old one, from 2002: https://www.dropbox.com/s/7rr9zdstxoxnuex/Tem_Isrc.jpg?raw=1 I wouldn't do it that way now. I'd replace it all with one part. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Wednesday, November 15, 2017 at 3:28:49 PM UTC-5, Jim Thompson wrote:
> On Wed, 15 Nov 2017 11:09:21 -0800, John Larkin > <jjlarkin@highland_snip_technology.com> wrote: > > >On Wed, 15 Nov 2017 11:06:16 -0700, Jim Thompson > ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > > > [snip] > >> > >>Why all that complexity? Plus the load behavior is inside your loop. > >>A dual R-R OpAmp plus either a PMOS or PNP for the high current will > >>easily solve your problem... and be stable. > >> > >> ...Jim Thompson > > > >How would that work? > > See "CurrentSourceConceptual.pdf" on the S.E.D/Schematics Page of my > website for a bidirectional source/sink version. Simplification to > single-sided is left as an exercise for the student ;-)
Jim, Do you need that first pair of Fets? (Assuming the opamp can handle the supply voltage.) You are just using current to transfer the voltage from low side to high side... which I like. George H.
> > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > To save time, Let's just assume I know everything.
On Wednesday, November 15, 2017 at 5:01:29 PM UTC-5, Steve Wilson wrote:
> George Herold <gherold@teachspin.com> wrote: > > > I made this nice VCCS from a differential amp (Ina134), > > resistor and opamp (opa134) feedback. It was good to > > 40 or 50 mA. Bad ass-ci. > > > gnd---RR---+--RR-----+ > > ||\ | > > +|-\ | > > Ina134 | >-(A)-+--Rset-+---output to gnd. > > +|+/ | > > ||/ /| | > > Vin--RR--+----RR---< +-----+ > > \| > > Buffer opa134 > > It's in AoE3. > > Rset sets the current/voltage ratio and the other R's are > > in the ina134. > > I was thinking about more current and added a power opamp > > in the (A) spot. Didn't work, the power opamp OPA544 railed > > at the wrong side.. or something. The ina134 spec sheet > > shows a fast buffer BUF634? Would that be better. > > (maybe I need to limit the voltage to the ina134?) > > > This bipolar current source has nice return to ground. > > It's got an output impedance of Rset. (less nice.) > > > George H. > > Here are two simpler ones that might interest you. > > Simple bipolar current source > > The first one is useful if you can lift the ground and insert a current > sense resistor. It takes a fairly wideband op amp to get to 1MHz. I have > set the values to deliver +/- 100 mA to a load of zero to 125 ohms. > > Modified Howland Current Pump > > The second one delivers +/- 500 mA to a grounded load. I did not mess with > getting it to run at 1 MHz, but the same techniques used in the first > version should work as well. > > Both circuits use a single op amp so there should be no problems with > feedback oscillations due to different GBW products. > > https://silvercell.000webhostapp.com/sed/4B6F8609.ZIP
OK got 'em. The nice thing about the INA134 (or equivalent) is that the precision resistors are built in. George H.
On Thu, 16 Nov 2017 06:22:10 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>On Wednesday, November 15, 2017 at 3:28:49 PM UTC-5, Jim Thompson wrote: >> On Wed, 15 Nov 2017 11:09:21 -0800, John Larkin >> <jjlarkin@highland_snip_technology.com> wrote: >> >> >On Wed, 15 Nov 2017 11:06:16 -0700, Jim Thompson >> ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> > >> [snip] >> >> >> >>Why all that complexity? Plus the load behavior is inside your loop. >> >>A dual R-R OpAmp plus either a PMOS or PNP for the high current will >> >>easily solve your problem... and be stable. >> >> >> >> ...Jim Thompson >> > >> >How would that work? >> >> See "CurrentSourceConceptual.pdf" on the S.E.D/Schematics Page of my >> website for a bidirectional source/sink version. Simplification to >> single-sided is left as an exercise for the student ;-) > >Jim, Do you need that first pair of Fets? (Assuming the opamp can handle >the supply voltage.) You are just using current to transfer the voltage >from low side to high side... which I like. > >George H. >>
The first set of FET's could just as well be bipolar's. Or, if you trust resistor ratios, just make the first stage a level translator to transform a 0 to +1V input into a +VCC to (+VCC-1V) signal (or whatever scale factor you want. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
George Herold <gherold@teachspin.com> wrote:

> On Wednesday, November 15, 2017 at 5:01:29 PM UTC-5, Steve Wilson wrote:
>> Both circuits use a single op amp so there should be no problems with >> feedback oscillations due to different GBW products.
>> https://silvercell.000webhostapp.com/sed/4B6F8609.ZIP
> OK got 'em. The nice thing about the INA134 (or equivalent) is that the > precision resistors are built in.
Yes. Laser trimmed, excellent tracking over temperature, wide operating voltage, good drive capability. Should work well in this application.
> George H.