Load seen by opamp

Started by Anonymous in sci.electronics.basics9 years ago 3 replies

Hi, 1)If i use an opamp with resistor feedback (for example in inverting configuration with gain -R2/R1), the output resistence seen by...

Hi, 1)If i use an opamp with resistor feedback (for example in inverting configuration with gain -R2/R1), the output resistence seen by opamp is one resistor of R2 value? 2)for an opamp used in noninverting configuration (with gain 1+R2/R1), the output resistance seen by opamp is R1+R2? Thanks in advance


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...


Can a capacitor let DC current through?

Started by vorange in sci.electronics.basics10 years ago 53 replies

1st question : Till now, I believed that capacitors only let AC signals through while blocking DC. But then, I saw a schematic whee they put a...

1st question : Till now, I believed that capacitors only let AC signals through while blocking DC. But then, I saw a schematic whee they put a capacitor on the output line of an opamp. The signal into the opamp was a square wave signal (which I imagine is DC and not AC). How then does the output of the opamp (presumably DC as well) pass through the capacitor? This has confused the hell o...


Opamp offset voltage problem

Started by Anonymous in sci.electronics.basics10 years ago 3 replies

Hi! I want to measure the offset voltage of an opamp. First, I configure the opamp in an unity gain buffer and measure the output. The offset...

Hi! I want to measure the offset voltage of an opamp. First, I configure the opamp in an unity gain buffer and measure the output. The offset voltage is 64.16uV. Then, I applied this voltage to the non- inverting input of the opamp. When I simulate it again, instead of getting 0V at the output, I get 464.29mV. Is the setup correct? Is the offset voltage of 64.16uV correct? Looks a bit small ...


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


confused about opamp circuit from practical electronics for inventors

Started by panfilero in sci.electronics.basics10 years ago 7 replies

hello, OK, I've been breaking my head over this one for a while and just can't figure it out. It's an example from a book called "Practical...

hello, OK, I've been breaking my head over this one for a while and just can't figure it out. It's an example from a book called "Practical Electronics For Inventors" It's basically a "Simple Triangle-wave/Square-wave Generator" It has a integrator opamp circuit feeding the non-inverting input on a positive feedback.... (schmitt trigger or comparator not about the terminology here) opamp ...


opamp voltage converter question

Started by Tom Del Rosso in sci.electronics.basics4 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 ...


Alternative voltage reference?

Started by MRW in sci.electronics.basics10 years ago 12 replies

Hi! I would like to know if there are other means to setup a voltage reference. I came up with this circuit: http://bayimg.com/iAeflAAbg The...

Hi! I would like to know if there are other means to setup a voltage reference. I came up with this circuit: http://bayimg.com/iAeflAAbg The purpose is to have a voltage divider (via a potentiometer) where the output swings from 2.5 to 2V. One way I came up with is by using an opamp voltage follower. Is there another way to design a voltage source without using an opamp? Thank you again...


neg ldo problems

Started by Hammy in sci.electronics.basics7 years ago 2 replies

I'm guessing I'm missing the obvious here. I'm trying to build a discrete negative LDO using a NFET for the pass element. I'm basing it on...

I'm guessing I'm missing the obvious here. I'm trying to build a discrete negative LDO using a NFET for the pass element. I'm basing it on the internal structure of the UCC284-5 seen here. http://i50.tinypic.com/orkroj.png I've tried inverting the output of the opamp with a BJT but its not regulating. The positive input to the opamp is tied to V4 which is a - 2.5V reference, feedback...


Opamp preamplifier design question

Started by MRW in sci.electronics.basics10 years ago 17 replies

I'm working with these microphones because I have them...

I'm working with these microphones because I have them already: http://www.knowlesacoustics.com/knowlesacoustics-apps/microphone_productdetail.do?product_id=12 Assuming that the voltage output of the mic at 40dB re 20 uPa is 5 microvolts, would using two opamp stages for a pre-amplifier circuit be suitable? I think 5 microvolts is too low, so I'm trying to step up the voltage to at least...


How does this circuit work? Is it a pre-amp?

Started by MRW in sci.electronics.basics10 years ago 20 replies

Hello! Happy 4th of July to my American colleagues! I have this circuit: http://bayimg.com/NaDlBAAbD How does it work? I initially...

Hello! Happy 4th of July to my American colleagues! I have this circuit: http://bayimg.com/NaDlBAAbD How does it work? I initially thought that the first opamp is a microphone pre-amplifier in an inverting configuration and the second one is used to invert the signal back. But when I looked at it again, the second opamp is configured as a voltage follower. Why is that? I think th...


How do you derive opamp equations if you flip the opamp in an inverting configuration?

Started by MRW in sci.electronics.basics10 years ago 11 replies

I'm actually curious because when I tried playing around with some circuit simulation I had accidentally interchanged the inverting...

I'm actually curious because when I tried playing around with some circuit simulation I had accidentally interchanged the inverting and non-inverting input in an inverting configuration. I knew my output was funky so I tried doing hand calculations and my equations came out the same. ?? Thanks!


can an opamp sink current

Started by panfilero in sci.electronics.basics8 years ago 3 replies

can an opamp sink current? I'm guessing yes, since I would guess there may be some kind of totem pole thing going on at the output and thats...

can an opamp sink current? I'm guessing yes, since I would guess there may be some kind of totem pole thing going on at the output and thats how regular 7400s roll at their output so... since 7400 can sink, opamps can sink.... ????


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.