# If an op amp can only amplify a signal within the boundaries of its power supply, why bother using the op amp instead of just using the power supply?

For example, if I want a 1V signal to be amplified to 10V, why would I make my life harder instead of just connecting the 10V power supply?

I know that op amps serve other purposes than amplifying signal. So another answer I am looking for is: Would there ever be a situation where you would use an op amp to strictly amplify a signal instead of using a power supply?

• ... Because then how do you amplify the signal when it drops to 0.5V? Oct 15, 2017 at 1:07
• Do you know what a signal is? Signal carries information. Modulating information into electricity with a power supply, while possible in some cases, is awkward. Yeah you can add a regulator after the power supply to do it, that's easier, but then that regulator would be a amplifier, and when you design it right it will be one of the classic amplifier designs. Oct 15, 2017 at 1:11
• a lot of control circuits (ICs, MCUs, etc) can't handle/steer 10v, so opamps scale digital levels to real world levels (eg: 3.3v ->12v) Oct 15, 2017 at 14:33

If you just want a 10 V output, yes, you can use a power supply.

But if you want an output that changes in response to an input (for example if when your input drops to 0.5 V you only want 5 V out), then you need something other than just a power supply. You want an amplifier. And in many scenarios, an op-amp (with an appropriate feedback circuit) is the kind of amplifier you want.

If you mean you want to turn a 1V DC level into 10V you would not normally use an op-amp.

If however you want to amplify an analog signal what varies continuously from zero to one volt by ten, you need an op-amp.

Op amps are used for a variety of purposes. The example you used to multiply a 1V supply to 10V seems to be a very specific scenario where you desire a fixed DC output. In reality, amplification often requires operation over a range of voltages - for example, amplifying 0-1V to 0-10V. In this situation you would require an amplifier rather than just using a specific PS value.

Even if you simply want to boost a fixed DC voltage, it is generally easier to incorporate an op amp to get the desired voltage than it is to modify the power supply. Especially if the circuit is going to require multiple voltage levels, it is easier to have a single power supply voltage and multiple op amp circuits.

Op amps are also useful due to their high input and low output impedance. See more here: What is input and output impedance of an opamp?