On Thursday, July 13, 2017 at 4:13:13 PM UTC+2, George Herold wrote:> On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: > > Marke wrote: > > > > ----------------- > > > > > > > > > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? > > > > > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. > > > > > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. > > > > > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. > > > > > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. > > > > > > To summarize: > > > > > > - Vin = +24V and/or 208VAC > > > - Vout= 100mV DC +/- 2mV > > > - Iout = up to 50mA into short circuit load<snip>> Right, that's what I'd try. If you need a lower source impedance > maybe buffer with an opamp. (Is there some dip opamp that does ~100mA > besides the TCA0372?.. too lazy to troll Digikey.)http://www.onsemi.com/pub/Collateral/MC33201-D.PDF comes close. The OP talks about a load that can source 50mA at +100mV, which seems to imply that he wants an op amp that can sink 50mA from +100mV into the negative rail (ground here) which is asking a bit much, even from the MC33201. You might be able to do it with an N-channel MOSFet - most op amps could drive a big-enough MOSFET gate hard enough to let the MOSFet sink 50mA to ground from +100mV. The capacitative load would make the circuit a pain to frequency compensate, and you'd probably have to dump in a few extra mA from the positve rail to keep everything tidy when the load was high impedance. The rest of thread makes it sounds as if he wants to deliver 50mA into the load at +100mV, which is much less difficult. -- Bill Sloman, Sydney
100mV DC supply
Started by ●July 13, 2017
Reply by ●July 13, 20172017-07-13
Reply by ●July 13, 20172017-07-13
On Thursday, July 13, 2017 at 11:27:49 AM UTC-4, bitrex wrote:> On 07/13/2017 09:10 AM, dagmargoodboat@yahoo.com wrote: > > On Thursday, July 13, 2017 at 3:32:23 AM UTC-4, Marke wrote: > >> Hi All, > >> > >> I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? > >> > >> Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. > >> > >> The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. > >> > >> I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. > >> > >> I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. > >> > >> To summarize: > >> > >> - Vin = +24V and/or 208VAC > >> - Vout= 100mV DC +/- 2mV > >> - Iout = up to 50mA into short circuit load > >> > >> Thank you, > >> > >> Mark > > > > Once you have +1.8V, why not something like this? > > > > > > (view in Courier font) > > +1.8V > > Vref >---. -+- > > | | > > [R1] [R4] 20 > > | 100mV |\ | > > +----------|+\ |/ Q1 > > | | >---[R3]----| > > [R2] .---|-/ |>. > > | | |/ | > > === | | > > '--------------------+-----> Vout = +100mV > > | > > [1k] R5 > > | > > === > > > > Vout is a precision, low-impedance output. R4 provides > > short-circuit protection. R5 provides an optional > > minimum load. > > > > Cheers, > > James Arthur > > > > Looks like a TL431...The TL431 is shunt, though, sucking maximum current all the time, and outputs 2.5V where the OP requested 100mV. Cheers, James Arthur
Reply by ●July 13, 20172017-07-13
On Thu, 13 Jul 2017 07:56:41 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Thursday, July 13, 2017 at 10:13:13 AM UTC-4, George Herold wrote: >> On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: >> > Marke wrote: >> > >> > ----------------- >> > >> > >> > > >> > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? >> > > >> > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. >> > > >> > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. >> > > >> > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. >> > > >> > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. >> > > >> > > To summarize: >> > > >> > > - Vin = +24V and/or 208VAC >> > > - Vout= 100mV DC +/- 2mV >> > > - Iout = up to 50mA into short circuit load >> > > >> > > Thank you, >> > > >> > > >> > >> > ** Using the KISS principle, all you need is a 5V, 1Amp TO220 reg IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types. >> > >> > The 120ohm & 82ohm go in parallel to make 48.7ohms, then 1ohm in series across 5V. >> > >> > This makes a 1:49.7 divider so you get 100mV with a 1 ohm source impedance and a SCC of 100mA. >> > >> > A small cap is also needed across the output of the reg IC for stability. >> > >> > >> > >> > .... Phil >> >> Right, that's what I'd try. If you need a lower source impedance >> maybe buffer with an opamp. (Is there some dip opamp that does ~100mA >> besides the TCA0372?.. too lazy to troll Digikey.) >> >> George H. > >I interpret the OP as needing 100mV and holding +/-3mV for currents of >0 <= i.out <= 50mA. Most op-amps would need a buffer for that, yes. >The buffer elininates opamp self-heating as a function of load current, which could be a big source of error. Of course, the buffer has to be inside the loop. Really low-noise amps need low-value feedback resistors to keep Johnson noise down, which implies a lot of opamp current even with no load. So sometimes one adds a buffer just to drive the feedback resistors. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●July 13, 20172017-07-13
On Thursday, July 13, 2017 at 10:56:48 AM UTC-4, dagmarg...@yahoo.com wrote:> On Thursday, July 13, 2017 at 10:13:13 AM UTC-4, George Herold wrote: > > On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: > > > Marke wrote: > > > > > > ----------------- > > > > > > > > > > > > > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? > > > > > > > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. > > > > > > > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. > > > > > > > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. > > > > > > > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. > > > > > > > > To summarize: > > > > > > > > - Vin = +24V and/or 208VAC > > > > - Vout= 100mV DC +/- 2mV > > > > - Iout = up to 50mA into short circuit load > > > > > > > > Thank you, > > > > > > > > > > > > > > ** Using the KISS principle, all you need is a 5V, 1Amp TO220 reg IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types. > > > > > > The 120ohm & 82ohm go in parallel to make 48.7ohms, then 1ohm in series across 5V. > > > > > > This makes a 1:49.7 divider so you get 100mV with a 1 ohm source impedance and a SCC of 100mA. > > > > > > A small cap is also needed across the output of the reg IC for stability. > > > > > > > > > > > > .... Phil > > > > Right, that's what I'd try. If you need a lower source impedance > > maybe buffer with an opamp. (Is there some dip opamp that does ~100mA > > besides the TCA0372?.. too lazy to troll Digikey.) > > > > George H. > > I interpret the OP as needing 100mV and holding +/-3mV for currents of > 0 <= i.out <= 50mA. Most op-amps would need a buffer for that, yes. > > If efficiency doesn't matter, just use an LM317 as the preregulator > with the Vadj terminal grounded. That gets you to 1.2V with one part. > An LMV431-1.2 with a 50mA-limiting resistor to +24V might even be > simpler (& more accurate) for getting to 1.2V. > > Cheers, > James ArthurSure... you know my opamp idea is probably not so good. I used an opamp as a voltage reference in a circuit and then found when I hung a bunch of bypass caps on the output... It sang for me. :^) Your circuit with transistor would be better. George H.
Reply by ●July 13, 20172017-07-13
On Thu, 13 Jul 2017 09:09:09 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Thursday, July 13, 2017 at 10:56:48 AM UTC-4, dagmarg...@yahoo.com wrote: >> On Thursday, July 13, 2017 at 10:13:13 AM UTC-4, George Herold wrote: >> > On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: >> > > Marke wrote: >> > > >> > > ----------------- >> > > >> > > >> > > > >> > > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? >> > > > >> > > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. >> > > > >> > > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. >> > > > >> > > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. >> > > > >> > > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. >> > > > >> > > > To summarize: >> > > > >> > > > - Vin = +24V and/or 208VAC >> > > > - Vout= 100mV DC +/- 2mV >> > > > - Iout = up to 50mA into short circuit load >> > > > >> > > > Thank you, >> > > > >> > > > >> > > >> > > ** Using the KISS principle, all you need is a 5V, 1Amp TO220 reg IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types. >> > > >> > > The 120ohm & 82ohm go in parallel to make 48.7ohms, then 1ohm in series across 5V. >> > > >> > > This makes a 1:49.7 divider so you get 100mV with a 1 ohm source impedance and a SCC of 100mA. >> > > >> > > A small cap is also needed across the output of the reg IC for stability. >> > > >> > > >> > > >> > > .... Phil >> > >> > Right, that's what I'd try. If you need a lower source impedance >> > maybe buffer with an opamp. (Is there some dip opamp that does ~100mA >> > besides the TCA0372?.. too lazy to troll Digikey.) >> > >> > George H. >> >> I interpret the OP as needing 100mV and holding +/-3mV for currents of >> 0 <= i.out <= 50mA. Most op-amps would need a buffer for that, yes. >> >> If efficiency doesn't matter, just use an LM317 as the preregulator >> with the Vadj terminal grounded. That gets you to 1.2V with one part. >> An LMV431-1.2 with a 50mA-limiting resistor to +24V might even be >> simpler (& more accurate) for getting to 1.2V. >> >> Cheers, >> James Arthur > >Sure... you know my opamp idea is probably not so good. >I used an opamp as a voltage reference in a circuit and then >found when I hung a bunch of bypass caps on the output... >It sang for me. :^) > >Your circuit with transistor would be better. > >George H.Some opamps, especially RRO types, are c-load stable. Almost any opamp is c-load stable with enough C! -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●July 13, 20172017-07-13
On Thursday, July 13, 2017 at 12:13:23 PM UTC-4, John Larkin wrote:> On Thu, 13 Jul 2017 09:09:09 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Thursday, July 13, 2017 at 10:56:48 AM UTC-4, dagmarg...@yahoo.com wrote: > >> On Thursday, July 13, 2017 at 10:13:13 AM UTC-4, George Herold wrote: > >> > On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: > >> > > Marke wrote: > >> > > > >> > > ----------------- > >> > > > >> > > > >> > > > > >> > > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? > >> > > > > >> > > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. > >> > > > > >> > > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. > >> > > > > >> > > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. > >> > > > > >> > > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. > >> > > > > >> > > > To summarize: > >> > > > > >> > > > - Vin = +24V and/or 208VAC > >> > > > - Vout= 100mV DC +/- 2mV > >> > > > - Iout = up to 50mA into short circuit load > >> > > > > >> > > > Thank you, > >> > > > > >> > > > > >> > > > >> > > ** Using the KISS principle, all you need is a 5V, 1Amp TO220 reg IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types. > >> > > > >> > > The 120ohm & 82ohm go in parallel to make 48.7ohms, then 1ohm in series across 5V. > >> > > > >> > > This makes a 1:49.7 divider so you get 100mV with a 1 ohm source impedance and a SCC of 100mA. > >> > > > >> > > A small cap is also needed across the output of the reg IC for stability. > >> > > > >> > > > >> > > > >> > > .... Phil > >> > > >> > Right, that's what I'd try. If you need a lower source impedance > >> > maybe buffer with an opamp. (Is there some dip opamp that does ~100mA > >> > besides the TCA0372?.. too lazy to troll Digikey.) > >> > > >> > George H. > >> > >> I interpret the OP as needing 100mV and holding +/-3mV for currents of > >> 0 <= i.out <= 50mA. Most op-amps would need a buffer for that, yes. > >> > >> If efficiency doesn't matter, just use an LM317 as the preregulator > >> with the Vadj terminal grounded. That gets you to 1.2V with one part. > >> An LMV431-1.2 with a 50mA-limiting resistor to +24V might even be > >> simpler (& more accurate) for getting to 1.2V. > >> > >> Cheers, > >> James Arthur > > > >Sure... you know my opamp idea is probably not so good. > >I used an opamp as a voltage reference in a circuit and then > >found when I hung a bunch of bypass caps on the output... > >It sang for me. :^) > > > >Your circuit with transistor would be better. > > > >George H. > > Some opamps, especially RRO types, are c-load stable. > > Almost any opamp is c-load stable with enough C!I once put a 100,000uF low e.s.r. capacitor on the output of a SMPS. It cleaned up the load-step response nicely. Cheers, James Arthur
Reply by ●July 13, 20172017-07-13
Thank you everyone for the input, very much appreciated. I am not overly concerned about efficiency in this design so dividing down a linear regulator does seem like a much easier approach. James: Thank you for the hint to view in courier font, i had wondered how the hell everyone on here was parsing this style of schematic. I think this would work well Bill: I definitely misspoke in saying that I need a load which can source 50mA, it is the simpler issue of driving a resistive load with +100mV and having it draw up to 50mA. John: Thank you for the input. Adding two extra wires for for a kelvin arrangement doesn't complicate matters too much so I'll throw together two test setups and see how much of a difference it makes. My plan at this point is to build several different topologies and compare. Probably overkill but I get to build up a few different quick test beds and I'm sure will learn more in the process. Mark
Reply by ●July 13, 20172017-07-13
On Thursday, July 13, 2017 at 12:13:23 PM UTC-4, John Larkin wrote:> On Thu, 13 Jul 2017 09:09:09 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Thursday, July 13, 2017 at 10:56:48 AM UTC-4, dagmarg...@yahoo.com wrote: > >> On Thursday, July 13, 2017 at 10:13:13 AM UTC-4, George Herold wrote: > >> > On Thursday, July 13, 2017 at 4:00:57 AM UTC-4, Phil Allison wrote: > >> > > Marke wrote: > >> > > > >> > > ----------------- > >> > > > >> > > > >> > > > > >> > > > I have a need to generate +100mV DC to drive a load which is capable of sourcing up to ~50mA but will typically see high impedance. Easily available I have a clean 24V source and 208VAC. My intent is to drop from 24V to ~1.8V using a buck converter then follow it up with a 1.0V precision shunt (ADR510 or other) followed by a 9:1 precision resistor divider. Buffer the 100mV output by a low noise single supply op-amp such as ltc1014. Although it looks like ltc1014 won't be able to source enough current so possibly followed with a BJT? > >> > > > > >> > > > Voltage drift is more important than precision for this application and +/- 3mV should be good enough. The environment the board will reside in is ~25C +/- 5deg. The output voltage must not drift above ~130mV to prevent causing issues in the test chamber. > >> > > > > >> > > > The voltage across the load is buffered, low-pass filtered (2-pole active = 1kHz) and multiplied by 10x before being sampled. The low pass filter frequency is chosen to preserve rise times in the ~500uS range. > >> > > > > >> > > > I expect that the largest source of noise will not be from the shunt (70ppm/C), the resistor divider (25ppm/C), or the Op-Amp ~160uV but from the 5 foot run of cable to the test chamber and back and am interested in best practice shielding techniques to mitigate induced noise. > >> > > > > >> > > > I'm not much of an electrical designer and haven't designed anything similar to this before so I'm interested in hearing about other possible topologies that can meet the requirements or how others would approach the problem. The solution will be put onto a pcb as part of a larger circuit so i cannot use a benchtop supply. > >> > > > > >> > > > To summarize: > >> > > > > >> > > > - Vin = +24V and/or 208VAC > >> > > > - Vout= 100mV DC +/- 2mV > >> > > > - Iout = up to 50mA into short circuit load > >> > > > > >> > > > Thank you, > >> > > > > >> > > > > >> > > > >> > > ** Using the KISS principle, all you need is a 5V, 1Amp TO220 reg IC and 3 resistors. The resistors are 120ohm, 82ohm and 1ohm - all 1% types. > >> > > > >> > > The 120ohm & 82ohm go in parallel to make 48.7ohms, then 1ohm in series across 5V. > >> > > > >> > > This makes a 1:49.7 divider so you get 100mV with a 1 ohm source impedance and a SCC of 100mA. > >> > > > >> > > A small cap is also needed across the output of the reg IC for stability. > >> > > > >> > > > >> > > > >> > > .... Phil > >> > > >> > Right, that's what I'd try. If you need a lower source impedance > >> > maybe buffer with an opamp. (Is there some dip opamp that does ~100mA > >> > besides the TCA0372?.. too lazy to troll Digikey.) > >> > > >> > George H. > >> > >> I interpret the OP as needing 100mV and holding +/-3mV for currents of > >> 0 <= i.out <= 50mA. Most op-amps would need a buffer for that, yes. > >> > >> If efficiency doesn't matter, just use an LM317 as the preregulator > >> with the Vadj terminal grounded. That gets you to 1.2V with one part. > >> An LMV431-1.2 with a 50mA-limiting resistor to +24V might even be > >> simpler (& more accurate) for getting to 1.2V. > >> > >> Cheers, > >> James Arthur > > > >Sure... you know my opamp idea is probably not so good. > >I used an opamp as a voltage reference in a circuit and then > >found when I hung a bunch of bypass caps on the output... > >It sang for me. :^) > > > >Your circuit with transistor would be better. > > > >George H. > > Some opamps, especially RRO types, are c-load stable. > > Almost any opamp is c-load stable with enough C!Huh, OK, I didn't know that. Too late now. (I think I had a dual opamp, so I inverted twice and rolled of the inverters with big C's.) George h.> -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●July 13, 20172017-07-13
Not to completely derail all the helpful discussion but google groups seems like a horrible way to view these topics. I assume most people use a usenet reader of some kind?
Reply by ●July 13, 20172017-07-13
