Forums

Opamp w/ Vsupply >36V

Started by George Herold July 15, 2013
On Thu, 18 Jul 2013 14:20:56 -0400, "Tom Del Rosso"
<tomd_u1@verizon.net.invalid> wrote:

> >John Larkin wrote: >> On Thu, 18 Jul 2013 12:43:12 -0400, "Tom Del Rosso" >> <tomd_u1@verizon.net.invalid> wrote: >> >> > >> > John Larkin wrote: >> > > >> > > The FTP thing didn't work well, so I'm using Dropbox now. Here's >> > > the HV amp idea: >> > > >> > > https://dl.dropboxusercontent.com/u/53724080/Circuits/Optos/HVamp.JPG >> > > >> > > I actually did it once, for the atom probe project, and it worked >> > > fine. >> > >> > What do you do with FB? >> >> Whatever you like. What you do with feedback is application dependant. > >Of course, but how? You must have had an equally clever way to isolate it.
I didn't need isolation in my application, just a lot of voltage swing. I think I actually ran +350 and -50 supplies, something like that. It was to set the bias voltages on two planes of a 2D delay-line detector, localizing the time and XY location of ion impacts onto a microchannel plate. I could have bought a couple of Apex high voltage opamps, but that wouldn't be sporting. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
On 18/07/13 15.51, John Larkin wrote:
...
> The FTP thing didn't work well, so I'm using Dropbox now. Here's the HV amp > idea: > > https://dl.dropboxusercontent.com/u/53724080/Circuits/Optos/HVamp.JPG > > I actually did it once, for the atom probe project, and it worked fine.
How about cascode coupling the phototransistors? * The phototransistors will get more bandwidth. * The phototransistors only have to withstand a few volts Vce. * The two high-voltage output transistors can be complementary - and common emitter or collector. /Glenn
On Fri, 19 Jul 2013 06:57:38 +0200, Glenn <glenn2233@gmail.com> wrote:

>On 18/07/13 15.51, John Larkin wrote: >... >> The FTP thing didn't work well, so I'm using Dropbox now. Here's the HV amp >> idea: >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/Optos/HVamp.JPG >> >> I actually did it once, for the atom probe project, and it worked fine. > >How about cascode coupling the phototransistors? > >* The phototransistors will get more bandwidth. > >* The phototransistors only have to withstand a few volts Vce. > >* The two high-voltage output transistors can be complementary - and >common emitter or collector.
You could use low voltage phototransistors cascoded with depletion fets, like a couple of LND150 or DN2530, and get more speed and current at 600 volts p-p. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote:
> Opamp Vsupply >36V >=20 >=20 >=20 > Hi all, I=92ve got a circuit with that uses an opa2134. I find myself p=
ushing the 36V supply limit and I=92m a little worried. So I went looking= for a similar opamp but with a bit more headroom. =20
>=20 > So specs might read, >=20 >=20 >=20 > Dual opamp >=20 > unity gain stable=20 >=20 > 4(+) Mhz BW (8MHz or more would be nicer) >=20 > 10 V/us slew (again more is better) >=20 > 20mA current (positive, again more would be nicer) >=20 > small input C ( <5pF would be nice.) >=20 > 8 pin dip preferred >=20 >=20 >=20 > Trolling digikey I found a few possible candidates. =20 >=20 >=20 >=20 > TLE2142 (6 MHz GBW) >=20 > TLE2072 (only 38 V supply, 11 pF input C) >=20 > OPA2604 (nice but 10 pF input C)=20 >=20 > (I=92ll order a few of each.) >=20 >=20 >=20 > There was also the LF412A, but a bit lacking is positive supply current. =
=20
>=20 >=20 >=20 > Any others that I might have missed? =20 >=20 >=20 >=20 > Thanks,=20 >=20 > George H.
Hi all, I finally had time to try out these other opamps. =20 (it was a fail on each one.) The TLE2142 was a sweet opamp. But I forgot about the bias current. =20 I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1uA o= f bias current means 10mV to 100 mV of DC offset. (not acceptable.) Too b= ad 'cause otherwise it was nice. The TLE2142 has an issue running near it's negative rail. It needed the ra= il to be -3.0 Volts to keep the DC offset below 5mV (When operated from -1.= 5 V's the offset was ~120mV!) The OPA2604 oscillated out of the box and needed a bit of feedback C to tam= e it. (not a problem.) But it also had a lot of 'issues' (ringy dingies) = when driving a coax cable. I mucked around with termination resistors (sou= rce and end.) but never got the 'ringies' down to an acceptable level. =20 So I figured I'd try over voltaging the opa2134's I've got the supply volta= ge up to 40V (36V max) and no magic smoke yet. :^) =20 I tired a few different pieces, and did a bit of turn on/off torture. =20 The circuit has now been running on the lab bench for several hours. Shoul= d I test with some elevated temperatures? =20 I'm thinking this opamp will be fine. (I'll design for 35 V supplies and w= orse case it'll only be a tad above 36 volts.) (tad =3D 400mV in this case) George H.
On Tue, 30 Jul 2013 08:11:59 -0700 (PDT), George Herold <gherold@teachspin.com>
wrote:

>On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote: >> Opamp Vsupply >36V >> >> >> >> Hi all, I&#2013266066;ve got a circuit with that uses an opa2134. I find myself pushing the 36V supply limit and I&#2013266066;m a little worried. So I went looking for a similar opamp but with a bit more headroom. >> >> So specs might read, >> >> >> >> Dual opamp >> >> unity gain stable >> >> 4(+) Mhz BW (8MHz or more would be nicer) >> >> 10 V/us slew (again more is better) >> >> 20mA current (positive, again more would be nicer) >> >> small input C ( <5pF would be nice.) >> >> 8 pin dip preferred >> >> >> >> Trolling digikey I found a few possible candidates. >> >> >> >> TLE2142 (6 MHz GBW) >> >> TLE2072 (only 38 V supply, 11 pF input C) >> >> OPA2604 (nice but 10 pF input C) >> >> (I&#2013266066;ll order a few of each.) >> >> >> >> There was also the LF412A, but a bit lacking is positive supply current. >> >> >> >> Any others that I might have missed? >> >> >> >> Thanks, >> >> George H. > >Hi all, I finally had time to try out these other opamps. >(it was a fail on each one.) >The TLE2142 was a sweet opamp. But I forgot about the bias current. >I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1uA of bias current means 10mV to 100 mV of DC offset. (not acceptable.) Too bad 'cause otherwise it was nice. > >The TLE2142 has an issue running near it's negative rail. It needed the rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from -1.5 V's the offset was ~120mV!) > >The OPA2604 oscillated out of the box and needed a bit of feedback C to tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingies) when driving a coax cable. I mucked around with termination resistors (source and end.) but never got the 'ringies' down to an acceptable level. > >So I figured I'd try over voltaging the opa2134's I've got the supply voltage up to 40V (36V max) and no magic smoke yet. :^) >I tired a few different pieces, and did a bit of turn on/off torture. >The circuit has now been running on the lab bench for several hours. Should I test with some elevated temperatures? >I'm thinking this opamp will be fine. (I'll design for 35 V supplies and worse case it'll only be a tad above 36 volts.) (tad = 400mV in this case) > >George H.
Sometimes we bootstrap the supplies of opamps that have the precision that we need but not the voltage swing. You can also make a compound amp out of a good, low-voltage opamp and an ugly brute. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Tue, 30 Jul 2013 08:11:59 -0700, George Herold wrote:

> The OPA2604 oscillated out of the box and needed a bit of feedback C to > tame it. (not a problem.) But it also had a lot of 'issues' (ringy > dingies) when driving a coax cable. I mucked around with termination > resistors (source and end.) but never got the 'ringies' down to an > acceptable level.
Did you try the compensation circuits given in the spec sheet? BB (TI) shows some input RC circuits that help when driving capacitive loads with this amplifier.
> So I figured I'd try over voltaging the opa2134's I've got the supply > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a few > different pieces, and did a bit of turn on/off torture. The circuit has > now been running on the lab bench for several hours. Should I test with > some elevated temperatures? I'm thinking this opamp will be fine. (I'll > design for 35 V supplies and worse case it'll only be a tad above 36 > volts.) (tad = 400mV in this case)
What kind of reliability do you need? If this is a short-term one-off, you can probably get away with this kind of brinksmanship. If it has to work for others over a longer time period - do everyone a favor and either use a part rated for higher voltage or modify your circuit (e.g. composite amplifier) such that the amplifiers aren't overstressed.
On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote:
> On Tue, 30 Jul 2013 08:11:59 -0700, George Herold wrote: >=20 >=20 >=20 > > The OPA2604 oscillated out of the box and needed a bit of feedback C to >=20 > > tame it. (not a problem.) But it also had a lot of 'issues' (ringy >=20 > > dingies) when driving a coax cable. I mucked around with termination >=20 > > resistors (source and end.) but never got the 'ringies' down to an >=20 > > acceptable level. >=20 >=20
=20
> Did you try the compensation circuits given in the spec sheet? BB (TI) > shows some input RC circuits that help when driving capacitive loads with > this amplifier.
No. I'm not sure it was the cable C that was the issue. (Only 3 foot of co= ax and shrinking that to a few inches didn't change a thing.) I did put 50= ohms in series. =20 =20
> > So I figured I'd try over voltaging the opa2134's I've got the supply >=20 > > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a few >=20 > > different pieces, and did a bit of turn on/off torture. The circuit has >=20 > > now been running on the lab bench for several hours. Should I test wit=
h
>=20 > > some elevated temperatures? I'm thinking this opamp will be fine. (I'l=
l
>=20 > > design for 35 V supplies and worse case it'll only be a tad above 36 >=20 > > volts.) (tad =3D 400mV in this case) >=20 >=20 >=20 > What kind of reliability do you need? If this is a short-term one-off, y=
ou
> can probably get away with this kind of brinksmanship. If it has to > work for others over a longer time period - do everyone a favor and eithe=
r=20
> use a part rated for higher voltage or modify your circuit (e.g. composit=
e
> amplifier) such that the amplifiers aren't overstressed.
Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. =20 We'll sell maybe 100 or so of these over several years. =20 So can you say anything more about the stress? What's the cause? =20 I tried hitting the one on the bench with a heat gun, and shorted the out= put. (The case rose to ~100 C. I should see what happens with only 36V.) = Hey, I'll stick it in a socket. That way if it does fry in the future it = can be replaced. (opamps are cheap.)=20 George H.
On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote:

> On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote: >> On Tue, 30 Jul 2013 08:11:59 -0700, George Herold wrote: >> >> >> >> > The OPA2604 oscillated out of the box and needed a bit of feedback C >> > to >> >> > tame it. (not a problem.) But it also had a lot of 'issues' (ringy >> >> > dingies) when driving a coax cable. I mucked around with termination >> >> > resistors (source and end.) but never got the 'ringies' down to an >> >> > acceptable level. >> >> >> >> Did you try the compensation circuits given in the spec sheet? BB (TI) >> shows some input RC circuits that help when driving capacitive loads >> with this amplifier. > > No. I'm not sure it was the cable C that was the issue. (Only 3 foot of > coax and shrinking that to a few inches didn't change a thing.) I did > put 50 ohms in series.
Ah - you hadn't mentioned that before. Hmmn - could you describe the ringing (amplitude, duration, ringing frequency)?
>> > So I figured I'd try over voltaging the opa2134's I've got the supply
>> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a few >> >> > different pieces, and did a bit of turn on/off torture. The circuit >> > has >> > now been running on the lab bench for several hours. Should I test >> > with >> > some elevated temperatures? I'm thinking this opamp will be fine. >> > (I'll >> > design for 35 V supplies and worse case it'll only be a tad above 36 >> > volts.) (tad = 400mV in this case) >> >> >> >> What kind of reliability do you need? If this is a short-term one-off, >> you can probably get away with this kind of brinksmanship. If it has >> to work for others over a longer time period - do everyone a favor and >> either use a part rated for higher voltage or modify your circuit (e.g. >> composite amplifier) such that the amplifiers aren't overstressed. > > Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll > sell maybe 100 or so of these over several years.
I'm pretty conservative when it comes to semiconductor voltages - I'd call 0.4V _less_ than rated voltage was brinksmanship. But I expect my designs to have "reasonably high" reliability (not medical/life support level). If you look at failure rate curves with voltage (and I admit I don't recall seeing any for more modern lower voltage opamps) they are climbing rapidly and smoothly in the vicinity of the rated voltage. Of course there is a significant amount of variation.
> So can you say anything more about the stress? What's the cause? > I tried hitting the one on the bench with a heat gun, and shorted the > output. (The case rose to ~100 C. I should see what happens with > only 36V.) Hey, I'll stick it in a socket. That way if it does fry > in the future it can be replaced. (opamps are cheap.)
If your customers are savvy enough to diagnose the problem, and replace the amplifier without damage to themselves or to the device or to whatever function they were meant to provide - sure. My users, while often PhDs, are most often not that electronically savvy. And down-time is expensive.
On Tue, 30 Jul 2013 18:27:09 +0000 (UTC), Frank Miles
<fpm@u.washington.edu> wrote:

>On Tue, 30 Jul 2013 11:12:30 -0700, George Herold wrote: > >> On Tuesday, July 30, 2013 12:51:41 PM UTC-4, cassiope wrote: >>> On Tue, 30 Jul 2013 08:11:59 -0700, George Herold wrote: >>> >>> >>> >>> > The OPA2604 oscillated out of the box and needed a bit of feedback C >>> > to >>> >>> > tame it. (not a problem.) But it also had a lot of 'issues' (ringy >>> >>> > dingies) when driving a coax cable. I mucked around with termination >>> >>> > resistors (source and end.) but never got the 'ringies' down to an >>> >>> > acceptable level. >>> >>> >>> >>> Did you try the compensation circuits given in the spec sheet? BB (TI) >>> shows some input RC circuits that help when driving capacitive loads >>> with this amplifier. >> >> No. I'm not sure it was the cable C that was the issue. (Only 3 foot of >> coax and shrinking that to a few inches didn't change a thing.) I did >> put 50 ohms in series. > >Ah - you hadn't mentioned that before. Hmmn - could you describe the ringing >(amplitude, duration, ringing frequency)? > >>> > So I figured I'd try over voltaging the opa2134's I've got the supply > >>> > voltage up to 40V (36V max) and no magic smoke yet. :^) I tired a few >>> >> > different pieces, and did a bit of turn on/off torture. The circuit >>> > has >>> > now been running on the lab bench for several hours. Should I test >>> > with >>> > some elevated temperatures? I'm thinking this opamp will be fine. >>> > (I'll >>> > design for 35 V supplies and worse case it'll only be a tad above 36 >>> > volts.) (tad = 400mV in this case) >>> >>> >>> >>> What kind of reliability do you need? If this is a short-term one-off, >>> you can probably get away with this kind of brinksmanship. If it has >>> to work for others over a longer time period - do everyone a favor and >>> either use a part rated for higher voltage or modify your circuit (e.g. >>> composite amplifier) such that the amplifiers aren't overstressed. >> >> Brinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll >> sell maybe 100 or so of these over several years. > >I'm pretty conservative when it comes to semiconductor voltages - I'd call >0.4V _less_ than rated voltage was brinksmanship. But I expect my designs >to have "reasonably high" reliability (not medical/life support level). >If you look at failure rate curves with voltage (and I admit I don't recall >seeing any for more modern lower voltage opamps) they are climbing rapidly >and smoothly in the vicinity of the rated voltage. Of course there is a >significant amount of variation. > >> So can you say anything more about the stress? What's the cause? >> I tried hitting the one on the bench with a heat gun, and shorted the >> output. (The case rose to ~100 C. I should see what happens with >> only 36V.) Hey, I'll stick it in a socket. That way if it does fry >> in the future it can be replaced. (opamps are cheap.) > >If your customers are savvy enough to diagnose the problem, and replace >the amplifier without damage to themselves or to the device or to whatever >function they were meant to provide - sure. My users, while often PhDs, >are most often not that electronically savvy. And down-time is expensive.
Have the required signal levels (and load) been mentioned, or just the supply voltages? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On Tue, 30 Jul 2013 08:11:59 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Monday, July 15, 2013 12:01:21 PM UTC-4, George Herold wrote: >> Opamp Vsupply >36V >> >> >> >> Hi all, I&#2013266066;ve got a circuit with that uses an opa2134. I find myself pushing the 36V supply limit and I&#2013266066;m a little worried. So I went looking for a similar opamp but with a bit more headroom. >> >> So specs might read, >> >> >> >> Dual opamp >> >> unity gain stable >> >> 4(+) Mhz BW (8MHz or more would be nicer) >> >> 10 V/us slew (again more is better) >> >> 20mA current (positive, again more would be nicer) >> >> small input C ( <5pF would be nice.) >> >> 8 pin dip preferred >> >> >> >> Trolling digikey I found a few possible candidates. >> >> >> >> TLE2142 (6 MHz GBW) >> >> TLE2072 (only 38 V supply, 11 pF input C) >> >> OPA2604 (nice but 10 pF input C) >> >> (I&#2013266066;ll order a few of each.) >> >> >> >> There was also the LF412A, but a bit lacking is positive supply current. >> >> >> >> Any others that I might have missed? >> >> >> >> Thanks, >> >> George H. > >Hi all, I finally had time to try out these other opamps. >(it was a fail on each one.) >The TLE2142 was a sweet opamp. But I forgot about the bias current. >I've got a variable source impedance (100k ,33k and 10k ohm) and the ~1uA of bias current means 10mV to 100 mV of DC offset. (not acceptable.) Too bad 'cause otherwise it was nice. > >The TLE2142 has an issue running near it's negative rail. It needed the rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from -1.5 V's the offset was ~120mV!) > >The OPA2604 oscillated out of the box and needed a bit of feedback C to tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingies) when driving a coax cable. I mucked around with termination resistors (source and end.) but never got the 'ringies' down to an acceptable level. > >So I figured I'd try over voltaging the opa2134's I've got the supply voltage up to 40V (36V max) and no magic smoke yet. :^) >I tired a few different pieces, and did a bit of turn on/off torture. >The circuit has now been running on the lab bench for several hours. Should I test with some elevated temperatures? >I'm thinking this opamp will be fine. (I'll design for 35 V supplies and worse case it'll only be a tad above 36 volts.) (tad = 400mV in this case) > >George H.
Sounds OK, but it would be better/funner to test the part to failure. Maybe it fails at 41, maybe it fails at 70. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation