help me in finding this output from a single op-AMP

[shaiqbashir]

Hi Guys!

well ! i want to use a single op-AMP with a +-15V DC supply. Remember that no other external DC supply is to be used except that.

and i want to get the following output.

Vo=Vi + 5

now what i have in my mind is this. That i make a voltage follower that is a unity gain amplifier. and i would get as a result:

Vo=Vi

and then for getting 5V more, i think i want to use a voltage divider with 1Mohm and 2Mohm resistor to reduce the 15V supply voltage to 5V and make its path to the output.

that is, 5V will be continouously supplied to the output, no matter whether the input Vi is present or not. When the input Vi will be provided , it would give me (Vi+5)  as an output.


Please make me correct if im wrong here. and help me in getting the required answer.

I shall be very thankful to u for this act of kindness.

Take carez and Good Bye!

[ante]

More homework shaiqbashir ?  ;)

[audioguru]

Hi Shaiq,
You said that you are going to connect the voltage divider to the output of an opamp?
Don't you mean its input? Then check the input bias current for the opamp that will load down or pull-up the 5V from the divider.

Don't you think that the extremely low output impedance and 20mA of current from the output of an opamp would laugh and smile at a little 667k, 5uA load?

If you disconnect the input from an opamp follower, what voltage do you think its output will be?