Single supply opamp calculations

Started by MRW in sci.electronics.basics10 years ago 9 replies

Hi, I'm doing some more opamp calculations just to get used to opamp golden rules some more. I decided to do an ideal analysis on an inverting,...

Hi, I'm doing some more opamp calculations just to get used to opamp golden rules some more. I decided to do an ideal analysis on an inverting, single-supply opamp: http://i14.tinypic.com/5xebi4w.jpg After applying some golden rules, I got the following equations: (V1 / R1) + (Vo / R2) - [ (Va * (R2 - R1) ] / (R1 * R2) = 0 Re-arranging the terms, I get: Vo / V1 = -(R2 / R1) + (Va * ...


opamp inputs

Started by panfilero in sci.electronics.basics5 years ago 20 replies

can anyone tell me how an opamp powered off of 9V, can be used to take meas= urements of really high voltages, like 100V? Like a DMM.... I...

can anyone tell me how an opamp powered off of 9V, can be used to take meas= urements of really high voltages, like 100V? Like a DMM.... I realize the o= pamp is floating and isolated from whatever its measuring, but the inputs o= f the opamp can't go over the rails of the opamps... right? but you can pro= be large votlages with DMMs.... what are these inputs referenced to? much thanx


LTSpice and OpAmp Oscillation

Started by M. Hamed in sci.electronics.basics8 years ago 3 replies

I've built a discrete transistor OpAmp, and when the input was off, I saw it oscillating. So, I got interested in OpAmp oscillation...

I've built a discrete transistor OpAmp, and when the input was off, I saw it oscillating. So, I got interested in OpAmp oscillation and compensation. The main criterion is that a Phase shift of 180 degrees occur when the loop gain is higher than 1. I tried to demonstrate that in LTSpice but couldn't. I'm not sure if it's an LTSpice limitation, or something I'm doing. I opened up the incl...


unstable opamp ringing oscillating and such

Started by panfilero in sci.electronics.basics7 years ago 18 replies

can anyone in here explain why a OpAmp could oscillate or become unstable if there are 2 poles before it reaches 0dB on a plot of gain vs...

can anyone in here explain why a OpAmp could oscillate or become unstable if there are 2 poles before it reaches 0dB on a plot of gain vs frequency? Here's what I've gathered thus far... there's a cap internal to the op- amp, that cap is there for some reason and it puts the dominant pole in the op-amp's transfer function. That pole also puts a 90deg phase shift on the output of the opamp...


Choosing voltage opamp

Started by Vitaliy in sci.electronics.basics11 years ago 28 replies

Hello, I'm looking to add the 2nd stage to photodiode transimpedance amplifier. All I want to achieve by 2nd stage is voltage gain...

Hello, I'm looking to add the 2nd stage to photodiode transimpedance amplifier. All I want to achieve by 2nd stage is voltage gain and capability to drive 50 Ohm loads. The first stage is OPA657. 1) a) Given power supply for opamp +-5V, should I select the opamp that has Io,max=> 200mA. I do expect Vpeak-to-peak,output to be 10V. b) Is that output current achievable only at maximum sup


opamp voltage converter question

Started by Tom Del Rosso in sci.electronics.basics5 years ago 6 replies

A simple level converter. It assumes the +4V supply can sink current, so why not just have 2 resistors between +4 and +10 and use the opamp as...

A simple level converter. It assumes the +4V supply can sink current, so why not just have 2 resistors between +4 and +10 and use the opamp as a buffer? +10V | | R | | |---------- | | | | R | | | | | GND ...


TCA0372 1A opamp stability probs?

Started by BobG in sci.electronics.basics6 years ago 11 replies

Anyone used a TCA0372 1A output opamp? Seems prone to oscillate? Does it need some minimum gain to be stable? I'm running it from +-15V,...

Anyone used a TCA0372 1A output opamp? Seems prone to oscillate? Does it need some minimum gain to be stable? I'm running it from +-15V, two equal resistor inverters in series, input is 10.00V reference, trying to make a +-10V pot rail supply. Its squirrelly. Would a BFC across the feedback R help?


RRIO OpAmp Recommendation?

Started by Jim Thompson in sci.electronics.basics3 years ago 15 replies

I need a rail-to-rail I/O OpAmp, 5V Vcc is fine, slow speed setting a current mirror. What would you guys in the discrete world recommend as...

I need a rail-to-rail I/O OpAmp, 5V Vcc is fine, slow speed setting a current mirror. What would you guys in the discrete world recommend as being well-behaved, no peculiarities, etc? (And readily available ;-) Thanks! ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations ...


G-Job Time, Need R-R I/O OpAmp

Started by Jim Thompson in sci.electronics.basics5 years ago 2 replies

G-Job Time, Need R-R I/O OpAmp... Slow, so low GBW is OK But need VCC > = 8V Recommendations? ...

G-Job Time, Need R-R I/O OpAmp... Slow, so low GBW is OK But need VCC > = 8V Recommendations? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048


Tying both inputs of an opamp to the output

Started by Mimawl in sci.electronics.basics4 years ago 6 replies

Is there a possibility of something undesireable happening if *both* the inverting and non-inverting inputs of an opamp are tied to the...

Is there a possibility of something undesireable happening if *both* the inverting and non-inverting inputs of an opamp are tied to the output? A possible scenario is when one unit of a dual or quad type is unused and tying both inputs to the output is convenient in the PCB layout.


filters

Started by John Larkin in sci.electronics.basics6 years ago 3 replies

This cool. Click on a box on one of the surfaces. http://tinyurl.com/3jyxpke Click "filter expert" then "dual supplies." Then click on a...

This cool. Click on a box on one of the surfaces. http://tinyurl.com/3jyxpke Click "filter expert" then "dual supplies." Then click on a box on one of the surfaces. I came up with a new-to-me filter architecture that *almost* works for me. It's a degenerated MFB lowpass, where the opamp itself replaces the usual opamp-r-c integrator. http://dl.dropbox.com/u/53724080/Circuit...


What do you do with unused opamps in a quad package?

Started by MRW in sci.electronics.basics10 years ago 5 replies

Hi all. I remember posting a question before regarding leaving opamp inputs open. From what I read, the inputs should be connected to...

Hi all. I remember posting a question before regarding leaving opamp inputs open. From what I read, the inputs should be connected to ground or some voltage source to have some meaningful output. So, if I used an IC with 4 opamps and only utilized 2 of them, does that mean that I have to ground the inputs of the other two and just leave the output open? Or do I connect the unused opamp ou...


Is it okay if I leave an opamp or comparator input open?

Started by MRW in sci.electronics.basics10 years ago 8 replies

I am curious if it is okay to leave an opamp or comparator inverting or non-inverting input open while the device is powered. Thanks!

I am curious if it is okay to leave an opamp or comparator inverting or non-inverting input open while the device is powered. Thanks!


4 transistor discrete opamp (LTspice problem or circuit problem?)

Started by Bill Bowden in sci.electronics.basics3 years ago 9 replies

Why doesn't this discrete 4T opamp run in LTspice at higher frequencies? It looks ok at 1Khz, but I get a 5 meg oscillation at 10K or more....

Why doesn't this discrete 4T opamp run in LTspice at higher frequencies? It looks ok at 1Khz, but I get a 5 meg oscillation at 10K or more. There are no oscillations with the input disconnected. Version 4 SHEET 1 880 680 WIRE 128 -112 32 -112 WIRE 192 -112 128 -112 WIRE 400 -112 192 -112 WIRE 512 -112 400 -112 WIRE 400 -96 400 -112 WIRE 32 -64 32 -112 WIRE 128 -16 128 -32 WIRE 128 ...


LTspice Tip

Started by Jim Thompson in sci.electronics.basics2 years ago 10 replies

As I work my way to a Universal OpAmp Spice Model that you only have to feed the subcircuit 10-12 numbers from the datasheet, I observe that...

As I work my way to a Universal OpAmp Spice Model that you only have to feed the subcircuit 10-12 numbers from the datasheet, I observe that LTspice struggles with what I would consider ordinary hyperbolic functions (bounded, all derivatives exist, are finite, and continuous)... making a straight line out of a transfer curve with soft limiting on each end... and churning... churning... churni...


Opamp resistor magnitude

Started by Gone Postal in sci.electronics.basics4 years ago 52 replies

I have a question about the magnitude of the two feedback resistors on opamps. I am familiar with how to determine the ratio of the resistors...

I have a question about the magnitude of the two feedback resistors on opamps. I am familiar with how to determine the ratio of the resistors to get the desired gain, whether inverting or not. What I'm trying to figure out is what determines the magnitude of the resistors involved? I've seen different circuits with resistors of, say thousands, tens or hundered of thousands and even one tha...


Re: Input Impedance OpAmp Circuit

Started by Jim Thompson in sci.electronics.basics7 years ago 2 replies

On Thu, 14 Oct 2010 16:05:37 -0700, "Joel Koltner" wrote: > "Jim Thompson" wrote in > message...

On Thu, 14 Oct 2010 16:05:37 -0700, "Joel Koltner" wrote: > "Jim Thompson" wrote in > message news:h4veb6hs9bcbnr96l38frlj94fosa53e13@4ax.com... > > (6) Shared a cubicle with Tom Frederiksen. We attacked each other's > > designs with a (friendly) vengeance... at a level of which Larkin > > would be brought to te


Low cost, small size DIP Instrumentation amplifier IC

Started by chetanthegreat in sci.electronics.basics10 years ago 8 replies

Hello folks, I am facing a bit of trouble regarding the signal conditioning part. The standard 3 Opamp instrumentation...

Hello folks, I am facing a bit of trouble regarding the signal conditioning part. The standard 3 Opamp instrumentation amplifier using TL084 I am planning to inculcate becomes very bulky considering all the resisters involved for gain adjustment and similar tasks. There are 6 of these circuits on the entire board, thus resulting in unusually large PCB for the project. ...


Bipolar current limit

Started by George Herold in sci.electronics.basics8 months ago 29 replies

OK this is perhaps overkill.. see footnote. So I've got an indicator LED (bi-color) the input is the error term from a thermal loop, and I turn...

OK this is perhaps overkill.. see footnote. So I've got an indicator LED (bi-color) the input is the error term from a thermal loop, and I turn that into an LED current. I was thinking it might be nice to turn up the gain on the current, but then I worried about burning out the LED with too much current from the opamp.* So I drew this up... and then added the diodes to stop the trans...


Simulating Power Bandwidth

Started by Jim Thompson in sci.electronics.basics3 years ago 24 replies

I'm trying to do a simulation to show power bandwidth for a (high power) OpAmp versus compensation capacitor. In the lab I would simply crank...

I'm trying to do a simulation to show power bandwidth for a (high power) OpAmp versus compensation capacitor. In the lab I would simply crank up the signal generator amplitude until the output became triangular rather than sinusoidal. Collect all the data for peak amplitudes versus frequency and then plot. Any ideas how I might do that automatically in a simulator, generating a family...