OP AMP question

[AMD Phreak]

I cant seem to find this in any of my text, maybe i am blind, but correct me if i am wrong, when you have an op amp supplied with 12VDC and it is fed a signal, theoretical max output voltage is 2VDC due to internal losses, correct?

[bluce ree]

while you output voltage TOTALLY DEPENDS ON THE CIRCUIT:


the theoretical output voltage is 12V - 1.414Volts = 10.586V

you can also buy "rail-to-rail" op amps which will do even better, more like 11V or better.

look up TL074 opamps on google--look at the data sheet, it's extremely cheap.

Remember that if you overdrive an opamp, it's output will clip.

is your circuit a Phase Inverter? An amplifier? A filter? A Buffer? A Mixer?

[AMD Phreak]

Doh i just read my post over.
I ment 2VDC lower than VCC +/-

The example circuit is a comparator.

[Lynx]

It is an amp. The output will always be larger than the inputs. HOwever an op amp is a subraction? system where it is the difference bettween th + and the - inputs that is amplified rather than the inputs them selves. The most commonly used op amp around today is probably the 741 chip if you are looking for one.

[AMD Phreak]

Originally posted by Lynx
It is an amp. The output will always be larger than the inputs. HOwever an op amp is a subraction? system where it is the difference bettween th + and the - inputs that is amplified rather than the inputs them selves. The most commonly used op amp around today is probably the 741 chip if you are looking for one.


Depending on how you connect the device up, yes.

Its all good now. I got a 94% on my theory final. :)

[bluce ree]

The 741 is only common in schools. The outputs can be smaller than the inputs, (ever heard of a divider? or a signal compressor?)

[Lynx]

Depends what you clasify the input as. i.e. the Diff bettween + and -

[bluce ree]

i was referring to an input signal waveform on one input and a dc voltage bias on the other.

you're referring to a differential amp (difference between the two inputs = output--that's pretty specific, I was referring to ANY amp.

[L337 M33P]

The operational amplifier operates as a comparator if there is no feedback to either input. If the inverting input is more positive than the non-inverting input, the output goes to -Vcc (minus about 2 V), and vice versa.

If there are negative feedback resistors arranged in a potential divider and the inverting input is connected between them, the gain of the Op-amp is (Rf/R1)+1 where Rf is the resistor between the output and inverting input, R1 is between the inverting input and the ground.

The other type of linear amplifier is an inverting one. There is a resistor between the input to the amp and the inverting input, and a resistor between the output and the inverting input. The equation for the gain of this type of amp is -Rf/Rin.

Positive feedback in Op-amps can be used to turn them into Schmitt triggers, but they're boring

hope this answers some questions - I'm doing Electronics A-Level ;)

[AMD Phreak]

Originally posted by L337 M33P
The operational amplifier operates as a comparator if there is no feedback to either input. If the inverting input is more positive than the non-inverting input, the output goes to -Vcc (minus about 2 V), and vice versa.



That is what i was looking for on verification. Our book teaches the 2 volt rule, but my instructor states that in practice, it really is around 1V.

Thanks though! :)

What is electronics A-Level?

I am studying Comptuer and Electronics Engineering Technology, or CEET at ITT.

[L337 M33P]

Some op-amps can indeed get closer to the supply rails but they are special types. Bog-standard ones got within 2 V of the rail.

A-level is the English equivalent of a college education - I am in a college studying for them :D

::Edit for crummy spelling::