| ??? 02/18/09 09:25 Modified: 02/18/09 09:49 Read: times |
#162536 - re: transfer function Responding to: ???'s previous message |
Andy Peters said:
Ap Charles said:
Yes I need that transfer function (Vout=V2) . I mentioned LMP2234 which has an absolute maximum spec says "+/-300mV maximum input differential voltage" (Do I really need to go with absolute maximum ratings?) .I conclude from this is that the opamp won't work. You need to go back to op-amp school. The maximum differential input voltage is the maximum voltage you can apply to the op-amp's input pins, + and -, and expect the device to function as an op-amp. Why? Because remember one of the Golden Rules of op-amps: the voltages at the input pins are always equal. Now the voltages at the op-amp input pins are rarely the [i]circuit's[/i] input voltages. The circuit includes the feedback and other resistors! So you can certainly have a difference amplifier that subtracts 12 V from 15 V. Look up difference amplifiers in the Horowitz and Hill book, "The Art Of Electronics." -a "Maximum Differential Input Voltage In theory, there is no connection at all between the two inputs of an operational amplifier. If the difference in voltage between the two inputs of the op amp is excessive (on the order of up to "as specified by datasheet") then things inside the op amp break down and current starts to flow between the two inputs. " 15V-12V =3V and 3V>> +0.3V(for LMP2234) ? , Yet missing the point? -Ap |
| 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 |