opamp inputs

Started by panfilero in sci.electronics.basics7 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


opamp voltage converter question

Started by Tom Del Rosso in sci.electronics.basics7 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.basics9 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.basics5 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.basics8 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.basics7 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.basics8 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...


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

Started by Bill Bowden in sci.electronics.basics6 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.basics4 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.basics6 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...


Bipolar current limit

Started by George Herold in sci.electronics.basics3 years 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.basics6 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...


New Behavioral Spice Model Posted

Started by Jim Thompson in sci.electronics.basics5 years ago 1 reply

A convenient element to approximate input-referred noise in an OpAmp Spice model. Just insert in series with one input, set en (noise floor) &...

A convenient element to approximate input-referred noise in an OpAmp Spice model. Just insert in series with one input, set en (noise floor) & Fn (1/F corner). See... InputReferredNoise.zip on the Device Models & Subcircuits Page of my website. ...Jim Thompson -- | James E.Thompson | mens | |...


Op Amp Comparator hysteresis

Started by panfilero in sci.electronics.basics7 years ago 15 replies

I see circuits that add hysteresis to op-amp comparators by putting a positive feedback resistor network that acts as a voltage divider to the...

I see circuits that add hysteresis to op-amp comparators by putting a positive feedback resistor network that acts as a voltage divider to the output. Am I right in thinking that this will only work if you have a negative rail? If your negative rail is grounded this aint gonna give you hysteresis... is there a way this would work with a single supply opamp? thanks!