Timeline for Remove DC offset from op-amp output to allow increase in gain
Current License: CC BY-SA 4.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 11, 2018 at 14:44 | comment | added | Phil | Sorry Olin. Ill add it as a comment / update next time. | |
| Jun 11, 2018 at 11:35 | history | edited | Dave Tweed | CC BY-SA 4.0 | appended answer 379254 as supplemental |
| Jun 11, 2018 at 11:32 | review | Close votes | |||
| Jun 12, 2018 at 11:44 | |||||
| Jun 11, 2018 at 11:17 | comment | added | Olin Lathrop | No, I'm not going to tilt my head sideways. -1 for the laziness, and closing as unclear since I'm not going to read the text now. Such is the result of thumbing your nose at the volunteer you seek a favor from. | |
| Jun 7, 2018 at 12:51 | history | edited | Phil | CC BY-SA 4.0 | added 599 characters in body |
| Jun 7, 2018 at 11:53 | history | edited | Phil | CC BY-SA 4.0 | edited body |
| Jun 7, 2018 at 11:06 | comment | added | Phil | Right, I have tried reducing the gain resistors by x10 so R4 = 100K, and R3 = 5K. This works ok gain = 20. When I reduce R3 to 1K to get a gain of 100 it doesn't work; Now the output of the first stage is severely reduced when checking with the scope. | |
| Jun 6, 2018 at 22:00 | comment | added | evildemonic | I would try adding a load of 10kΩ and see if it improves things. Not this particular amp, but I have had opamps get screwy like this without some load. As others have mentioned, reducing the feedback impedance 10 or 100 fold might also get it to behave. | |
| Jun 6, 2018 at 18:30 | comment | added | Phil | No load on X2, just a oscilloscope probe. | |
| Jun 6, 2018 at 18:00 | comment | added | evildemonic | What kind of load did you have attached while making these measurements? | |
| Jun 6, 2018 at 15:29 | comment | added | Phil | Using 2x TSV992IST, 3.3v supply actually not the 5V on the picture | |
| Jun 6, 2018 at 14:26 | comment | added | Andy aka | What op-amps are you using and what supplies are they using? | |
| Jun 6, 2018 at 14:23 | comment | added | Phil | Thanks for the feedback. Would lower value resistors improve the circuit? | |
| Jun 6, 2018 at 13:53 | comment | added | LvW | Why are you using such large resistor values (50k, 1 meg); why not 5k and 100k? | |
| Jun 6, 2018 at 13:53 | comment | added | Sven B | My first suspect of saturation voltage at the output is usually something that went wrong in the feedback path (ie. around R4). Definitely check that everything's connected there as well. | |
| Jun 6, 2018 at 13:51 | answer | added | Spehro 'speff' Pefhany | timeline score: 1 | |
| Jun 6, 2018 at 13:51 | comment | added | Neil_UK | that 680pF is all you need to remove DC from the second stage. If it's not working, it's a dud. Remove R3 and the 680pF, and observe the output voltage. That's what the DC output should be with both R3 and 680pF in place, if the 680pF is working properly. | |
| Jun 6, 2018 at 13:37 | review | First posts | |||
| Jun 6, 2018 at 14:47 | |||||
| Jun 6, 2018 at 13:36 | history | asked | Phil | CC BY-SA 4.0 |