| ??? 02/17/09 08:02 Read: times |
#162502 - I explain it again Responding to: ???'s previous message |
Oliver Sedlacek said:
So what's all the circuitry for if Vout = V2? Why bother with V1?
Please see below. Oliver Sedlacek said:
If you want an opamp that works with the inputs at a substantially high voltage than the supply, then the Linear Technology "Over the top" family is what you want. If you want to look at other opamps, might I suggest my Opamp chooser Thanks Thats helpful , but I have an access to AD and Ti parts Microchip is good but sourcing will become a problem . Kai Klaas said:
Sorry, but I cannot see the point. You have an input voltage of 0...5V, to do what? A rail-to rail OPamp powered by Vcc=5V should easily accept this input voltage range. And if not, use a voltage divider at non-inverting input to keep the input voltage well within the recommended common mode input voltage range.
Ap said:
I mentioned LMP2234 which has an absolute maximum spec says "+/-300mV maximum input differential voltage". Normally, the differential input voltage is nearly zero, due to the action of feedback. And if there is a relevant differential input voltage, then your input resistors can limit the resulting current. Sorry, but this all makes no sense to me. Please explain, what input voltage you have, and what your OPamp shall do with it. Take care, there is an input voltage range which keeps your OPamp safe and there's an input voltage range which keeps your OPamp linearily working. An example: Good old LM324 accepts input voltages up to 32V, independently of supply voltage, without resulting in destroyed inputs. But you must keep the input voltage below Vcc-1.5V to make the OPamp work in the linear region. Kai Thanks for the help! I think I am not clear enough in explaining,actually I have as follows; 1) Signal output which is w.r.t its own reference provides a linear output 0-5V . The reference which I have is 15V(+/-1V or so) . Now as I need 0-5V the signal looks like 15V+0 to 15V+5V . To interface it to my uC ADC I tried to do (15V+0 to 15V+5V)-15v=Vout but here the opamp input side seems to be having voltages above its supply rail 5V . Please see OP777 I just found this, page 12 Fig 11 , is this the kind of topology to be adopted as per info above? with Opamps power supply rail being 5V or should I replace my schematic opamp with Op777. Regards/ 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 |