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: ...
How about cascode coupling the phototransistors?
/Glenn
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
ushing the 36V supply limit and I?m a little worried. So I went looking for a similar opamp but with a bit more headroom.
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 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.
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. :^) 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. Shoul d I test with some elevated temperatures? 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 = 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
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.
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.
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.
h lou
r eBrinksmanship(?).. It's only 0.4V?.. and that's for worst case. We'll sell maybe 100 or so of these over several years.
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 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.)
George H.
Ah - you hadn't mentioned that before. Hmmn - could you describe the ringing (amplitude, duration, ringing frequency)?
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.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.
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
It'll fail at 2.5 "tads", on a humid Sunday, just after midnight, when lightning strikes 3 miles away >:-} ...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.
) f
ging
Better than that here's some 'scope shots!
So I?m looking at avalanche breakdown voltages with different quenching r esistors (100k and 10 k) the first two ?scope shots are with the opa2134
100k ohm //bayimg.com/MaoKGaaEA 10k ohm //bayimg.com/NAoKDAAeaOh and here?s the TLE2142 with 10 k ohm //bayimg.com/nAOKGaaEa
And now the opa2604 first 100 k //bayimg.com/naokHaAEa and 10 k //bayimg.com/naOkjaaea
This is before I added a 50 ohm series resistor. That gave the bumps a lon ger period but a bit higher amplitude.
y wit
, . l sll
y r .Grin.. well PhD's are often less of the 'hand's on' type. But the circuit is pretty easy. I made it through hole, so if someoen wanted to change thi ngs it would be easier.
The ugly pot in the middle will go away. (just changing the supply voltage .) I let it cook over night at ~100C. no issues in the morning.
I'll test the heat again with lower supply voltage (but with the palstic co ver in place.)
So what type of PhD's do you service? Can you tell us where you work? George H.
f pushing the 36V supply limit and I?m a little worried. So I went look ing for a similar opamp but with a bit more headroom.
t.
A of bias current means 10mV to 100 mV of DC offset. (not acceptable.) To o bad 'cause otherwise it was nice.
rail to be -3.0 Volts to keep the DC offset below 5mV (When operated from
-1.5 V's the offset was ~120mV!)
tame it. (not a problem.) But it also had a lot of 'issues' (ringy dingie s) when driving a coax cable. I mucked around with termination resistors ( source and end.) but never got the 'ringies' down to an acceptable level.
ltage up to 40V (36V max) and no magic smoke yet. :^)
ould I test with some elevated temperatures?
d worse case it'll only be a tad above 36 volts.) (tad = 400mV in this ca se)
Well I could go a bit higher. (power from Phihong 48V wall wart.) But other parts might start to break too. (There's an ref102 that goes to
40V so I might loose that before the opamp.)George H.
Hmmn, just noticed that the GBW of the TLE2142 is about 1/4 of the OPA2604 GBW. That might be part of why you see the problem with the OPA but not the TLE. The 'ring', after all, is near the unity-gain BW of the TLE. And you only see the problem with some length of coax attached? Does it occur with no coax, just probing with a good low-Cin 10x or FET probe? Could you plug in a much faster amplifier while temporarily running at a lower voltage to see if there's a problem with your circuit or its implementation?
If you really like the TLE2142 - how about compensating for the input bias? Yes, it would cost a tweak.
Ok, that seems simple and your users are presumably knowledgeable about antistatic issues, etc.
Ah... the devices we design and build are for a collection of neuroscientists. Many have some electronics skills but most of them have enough on their minds trying to understand and/or manipulate the brain.
s t
ng
l . 4the TLE.
ycoax,
uch faster
a problem
Thanks for all the advice. I just can't 'spend' anymore time on this proje ct. (As much as I'd like to chase down the different opamp weirdnesses.) RE the TLE2142 and bias current. It's a simple buffer, with switched input resistors to ground on the front end. I don't know how I could compensate for the current.. would I have to put switched resistors in the feedback? 100k ohm of feedback may come with it's own problem.
For the opa2604 ringies it's there with no coax. (just a double male barre l connector into scope.) Alas I have no low C probes. (The 'best' x10 has 16pF)
s?
e o . cists.
Thanks, sounds interesting. There was a research/ medical doctor/ biologi st who came visiting. I was looking at the step response of an amplifier o n the 'scope. And I told him it was a two pole butterworth low pass. "Hmm", he says, "the delay looks a bit long there." pointing at the trace. "Oh there's also a series 1 k ohm resistor in the circuit so maybe that slo ws it down.", I respond. I shorted out the 1 k ohm. And he was happy. Now that's something you don't see every day. A doctor who *really* knows his step response. (Needless to say, they do a lot of electronics in his l ab.)
George H.
You only need to provide a current source at the opamp input. According to the datasheet this current is pretty stable so you might be able to get away with a resistor between amplifier and tweak wiper, and the tweak element ends between ground and the appropriate supply voltage. If you need a higher impedance value you can always connect the resistor to a bipolar transistor's emitter, and take the compensation current from the transistor's base, using the beta to reduce the current and increase the impedance.
But it's always important to recognize when to stop working on something.
I haven't seen any I/O _specifications_.
I'd attack it with a suitable OpAmp meeting the input current requirements and tack on a discrete output stage that would be unperturbed by the "HV". ...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.
Ahh, (silly me.) Well that's an easy tweak. I'll give it a try. (The board needs another spin to make some solder holes bigger anyway.)
Sometimes that's the hardest thing to know. (When it's time to stop.)
George H.
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