| ??? 02/18/09 15:28 Modified: 02/18/09 16:38 Read: times |
#162549 - If the feedback loop doesn't work... Responding to: ???'s previous message |
Ap said:
I have a question, thats when is the differential input maximum voltage gets violated as the opamp always tries to maintain similar voltages at its input terminals? Have a look at the scheme again: 
Consider the second OPamp. Its output voltage can only rise to Vcc = 5V in our example. So, the voltage at inverting input can only rise to 1.1628V. When the voltage at non-inverting input goes beyond 1.1628V for some reason, then the differential input voltage is no longer zero! Input voltage range violations often result from unlimited input voltages (real world!) or also from fast step changes, when the OPamp is too slow to follow. So, not only the input voltage has to be limited too safe values, but also low pass filters need to added to allow the OPamp's finite rise time to "control" the feedback loop in time. The rise time of input filter should be well below the rise time of OPamp, in critical (real world) applications. Kai |
| Topic | Author | Date |
| Opamp question | 01/01/70 00:00 | |
| Please specify! | 01/01/70 00:00 | |
| Oops here its | 01/01/70 00:00 | |
| Mistake? | 01/01/70 00:00 | |
| transfer function | 01/01/70 00:00 | |
| Vout = V2 ? | 01/01/70 00:00 | |
| I 'm entirly confused... | 01/01/70 00:00 | |
| I explain it again | 01/01/70 00:00 | |
| So Vout = V2 - V1 | 01/01/70 00:00 | |
| I do have a common GND | 01/01/70 00:00 | |
| So Vout = V2 -15 ? | 01/01/70 00:00 | |
| trying to achieve | 01/01/70 00:00 | |
| Reference | 01/01/70 00:00 | |
| Reference | 01/01/70 00:00 | |
| Much clearer but.. | 01/01/70 00:00 | |
| Not clear | 01/01/70 00:00 | |
What VOut range do you want? | 01/01/70 00:00 | |
| I think this will do the trick... | 01/01/70 00:00 | |
| re: transfer function | 01/01/70 00:00 | |
| re: transfer function | 01/01/70 00:00 | |
| Ohm's law | 01/01/70 00:00 | |
| Oh the internal protection of opamp! | 01/01/70 00:00 | |
| Errr... | 01/01/70 00:00 | |
| Don't confuse "OPamp" with "OPamp circuit"! | 01/01/70 00:00 | |
| Don't confuse "OPamp" with "OPamp circuit"! | 01/01/70 00:00 | |
| If the feedback loop doesn't work... | 01/01/70 00:00 |