LT Spice opamp a liittle weird

Started by John Larkin in sci.electronics.design5 years ago 21 replies

I was wondering about the power dissipation of an opamp, driving a sine wave into a mainly inductive load. See below. The first few...

I was wondering about the power dissipation of an opamp, driving a sine wave into a mainly inductive load. See below. The first few cycles current limit or something. I'm using UniversalOpamp2 with current limit 2 amps and rail=0. This opamp isn't documented in the HELP, or much anywhere else. Peak current is under 700 mA, so why is it clipping? Higher supply voltage helps. ...


capacitive loading an opamp

Started by John Larkin in sci.electronics.design11 years ago 85 replies

A few opamps are specifically spec's to drive any capacitive load, like LM8261 for instance. And sometimes you'll see an opamp that...

A few opamps are specifically spec's to drive any capacitive load, like LM8261 for instance. And sometimes you'll see an opamp that is loaded with a big cap to ground, in an appnote for example. If an opamp has some internal compensation node, midway through, that's the dominant pole, adding a cap on the output makes a second pole in the loop, potentially unstable. A huge cap might be s...


Apex HV opamp issues.

Started by George Herold in sci.electronics.design8 years ago 50 replies

Hi guys (and dolls), So if you read in JL's TI opamp thread, I am having noise issues in our laser diode. I turns out (I think) that the extra...

Hi guys (and dolls), So if you read in JL's TI opamp thread, I am having noise issues in our laser diode. I turns out (I think) that the extra noise is coming from my Piezo drive. The original circuit used a PA141 from Apex. (I can't find a schematic on-line, but I have a hard copy.) Several years ago this HV opamp went away and the recommended replacement from Apex was the PA314 http...


Class B distortion

Started by Anonymous in sci.electronics.design8 years ago 48 replies

Something I thought I knew, but am left puzzling... Take a simple class B output pair driven directly by an opamp. Result is na= sty crossover...

Something I thought I knew, but am left puzzling... Take a simple class B output pair driven directly by an opamp. Result is na= sty crossover distortion. Now, the nfb is taken from the circuit's output t= erminal, not from the opamp's output, so surely an ideal opamp should corre= ct for the 0.6v Vbe drops. Question is why doesn't it? The other question is what strategies exist to tackle...


Does the noise density function increase if an OpAmp goes into slew rate limit?

Started by RobertMacy in sci.electronics.design8 years ago 61 replies

Trying to sort out circuit simulation artifact from something that may be real. Does the noise come up [because of the inability of the...

Trying to sort out circuit simulation artifact from something that may be real. Does the noise come up [because of the inability of the OpAmp to reduce] when the OpAmp is driven too fast at too large a signal level? Circuit is a simple LT1028 in an 'inverting' configuration with power of +/-12Vdc. GNDed non-inverting input. Rinput = 1k. Rfdbk = 1k. Cfdbk = 20pF. Load is a simple ...


RRIO OpAmp Recommendation?

Started by Jim Thompson in sci.electronics.design8 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 ...


OPA552 as power regulator

Started by John Larkin in sci.electronics.design4 years ago 42 replies

I need some programmable power supply rails, maybe -5 to +40 volts or so. We have some OPA552s in stock, a nice 60 volt power opamp. It's...

I need some programmable power supply rails, maybe -5 to +40 volts or so. We have some OPA552s in stock, a nice 60 volt power opamp. It's a decomp, and it will be driving a big capacitive load, so there is an oscillation hazard. One of my guys got the model from TI and kluged it into LT Spice. The symbol is ugly but it seems to work. We don't know how to make it look like a real opamp. ...


Isolated high voltage opamp

Started by bitrex in sci.electronics.design7 years ago 21 replies

So I have a need for an analog isolation amplifier thing into a HV section at low audio frequencies. I remembered the "HV opamp" thing that...

So I have a need for an analog isolation amplifier thing into a HV section at low audio frequencies. I remembered the "HV opamp" thing that John Larkin posted a while back and that seems to work well, but I'd like to isolate the feedback via pwming it and sending it back across the barrier via an optocoupler and integrating. I dont really want to chop it first and have more LV elec...


HV OpAmp

Started by Jim Thompson in sci.electronics.design7 years ago 26 replies

HV OpAmp... Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher voltage devices. ...

HV OpAmp... Can be built to arbitrary HV supplies, just change Q1 and Q2 to higher voltage devices. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC


Using consumer-grade power amp as Power opamp

Started by Dave M in sci.electronics.design5 years ago 44 replies

Has anyone used any of the consumer-grade audio power amps such as the LM1825, TDA2030, or TDS7297 as a basic DC power opamp? Any reason they...

Has anyone used any of the consumer-grade audio power amps such as the LM1825, TDA2030, or TDS7297 as a basic DC power opamp? Any reason they shouldn't be used as power supply regulators, TEC controllers, etc? Dave M


Opamp offset question

Started by Klaus Kragelund in sci.electronics.design10 months ago 31 replies

Hi I have a PT1000 circuit where a LMV358 is used in a differential coupling to feed it to an ADC PT1000 is pull up with a resistor I...

Hi I have a PT1000 circuit where a LMV358 is used in a differential coupling to feed it to an ADC PT1000 is pull up with a resistor I would NOT do it like that, this is a design I have inhireted Problem is the large offset voltage of the opamp is amplified producing large errors We are contemplating production calibration, but I am worried that the offset isn't stable after the cali...


nice fA opamp

Started by John Larkin in sci.electronics.design6 years ago 21 replies

http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overv iew Input current is typically 0.1 fA at...

http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overv iew Input current is typically 0.1 fA at room temp. Noise and offset specs are impressive for a fA opamp. 0.1 fA is 625 electrons per second. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http:/


Yet Another Jellybean Opamp

Started by Allan Herriman in sci.electronics.design7 years ago 19 replies

Hi, I'm looking for a single supply jellybean opamp to meet the following requirements: V supply = 5.0V Vin (e.g. Vicm) 0V to 4V. Iin...

Hi, I'm looking for a single supply jellybean opamp to meet the following requirements: V supply = 5.0V Vin (e.g. Vicm) 0V to 4V. Iin +/- 100pA max. (prefer < 10pA) Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C, up to $2 for a dual, etc.. Here's the hard part: I want the Iin spec to apply over the Vin range *even when the supply voltage is zero*. Th


op-amp-controlled MOSFET cucrrent-source

Started by Winfield Hill in sci.electronics.design3 years ago 23 replies

Have you seen an analysis of the classic op-amp-controlled MOSFET current-source? I needed this for a design, plus I'd like to squeeze it...

Have you seen an analysis of the classic op-amp-controlled MOSFET current-source? I needed this for a design, plus I'd like to squeeze it into the x-Chapters, before the mid-August printing deadline. https://www.dropbox.com/s/nednxac2bykld8q/opamp-MOSFET_current-source.pdf?dl=1 In the formulas, I assume the opamp's output signal is controlled by Vin-Vs and R2 C2. I'm still ch...


Interfacing an OpAmp to a differential VCA

Started by Fibo in sci.electronics.design6 years ago 5 replies

Greeting, I'm having trouble interfacing an OpAmp (OPA378) to a Voltage Controlled Amplifier IC (VCA822). My signal coming out of the OPA378 is...

Greeting, I'm having trouble interfacing an OpAmp (OPA378) to a Voltage Controlled Amplifier IC (VCA822). My signal coming out of the OPA378 is riding on a 2.5V DC bias. I have a 22uF cap to cancel the 2.5V bias but with the cap there the input of the VCA822 floated to -3.3V. I then added a 12.7k resistor to ground after the cap which helped remove the -3.3V offset, but my output si


PSpice worst case simulation

Started by Joerg in sci.electronics.design12 years ago 36 replies

Hi Folks, Reached an end of a rope here: How do you make a worst case simulation in PSpice (or even Monte Carlo for that matter) properly find...

Hi Folks, Reached an end of a rope here: How do you make a worst case simulation in PSpice (or even Monte Carlo for that matter) properly find the extremes for an opamp offset voltage and input bias current? For example, for the opamp we have: VOS: Offset voltage VOS_DIST: Distribution, I assume VOS_NTOL: What gets entered here? VOS_PTOL: ... and here? If I enter 7mV or whatever f...


new (to me) all-pass circuit

Started by John Larkin in sci.electronics.design4 years ago 27 replies

It occurred to me that, in the conventional opamp all-pass 90 degree phase shifter...

It occurred to me that, in the conventional opamp all-pass 90 degree phase shifter circuit, https://www.dropbox.com/s/nfwd32p3z61g15y/90_degree.JPG?raw=1 a fast signal passes through all the opamp stages, so all the amps have to be fast. In this one, https://www.dropbox.com/s/rulyvlt072k49cp/New_All-Pass_1.jpg?raw=1 the fast signals just rip through the big caps in the slow stage...


how to tell if opamp is unity gain stable

Started by panfilero in sci.electronics.design10 years ago 19 replies

hello, does anyone know how to tell if an opamp is unity gain stable? My guess is= to check out the open loop phase margin and make sure...

hello, does anyone know how to tell if an opamp is unity gain stable? My guess is= to check out the open loop phase margin and make sure it's over... I dunno= ... about 30 degrees... is this it? Don't most opamps have decent open loo= p phase margin? Should I be saying open loop phase margin or does just say= ing phase margin imply that you are talking about the open loop phase margi= ...


LT Spice universal opamp

Started by Anonymous in sci.electronics.design3 years ago 5 replies

In universalopamp2, what does the "rail" parameter do? -- John Larkin Highland Technology, Inc The cork popped merrily,...

In universalopamp2, what does the "rail" parameter do? -- John Larkin Highland Technology, Inc The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"


little photo diodes and an opamp?

Started by George Herold in sci.electronics.design3 years ago 16 replies

The project seems to call for the smallest detectors. I'm buying a few each of 'all'* the little PD's from digikey. (I can share a list if...

The project seems to call for the smallest detectors. I'm buying a few each of 'all'* the little PD's from digikey. (I can share a list if someone wants... it's a mix of TH and SMD.) C_in between 1-3 pf when reversed biased. I don't see how it makes sense to bootstrap or cascode the PD**. So I was looking at opamps with small C-in. (Big thanks to H&H of AoE as always.) I've now g...