Operational Amplifier as DC Amplifier

For more info: https://www.hackster.io/electroboy001/operational-amplifier-as-dc-amplifier-1041a3

Adjustable op-amp DC amplifier board

Operational amplifiers are awesome, they are used to design a lot of circuits. In a previous part we discussed the open-loop gain / comparator feature of an op-amp, and now we will see the use of an operational amplifier to amplify a very small signal with adjustable gain. In the end we will make a DC amplifier which can be tuned easily through the onboard potentiometers.

Op-amp configurations and gain

There are two types of configurations (inverting and non-inverting) while using the op-amp in closed loop. Both configurations use negative feedback because it helps to minimize the error/noise and increase the overall stability. In the non-inverting configuration the signal is given on the non-inverting terminal and the gain is 1+Rf/Rin. In the inverting configuration the signal is applied on the inverting input, so the output is 180 degrees out of phase and the gain is −Rf/Rin.

In closed loop the op-amp tries to minimize the error of the applied input signal, the virtual ground concept. If the inverting terminal is held at ground potential, then the non-inverting terminal is also assumed at ground.

A basic DC amplifier working concept

Let's take an example where we have a signal of 10mA and we want to amplify it to 1 volt, so a gain factor of 100 is required.

Step 1: choose the configuration, here I am choosing non-inverting, which gives 1+Rf/Rin.

Step 2: choose Rf and Rin assume Rin = 1k, so we require Rf = 99k for a gain of 100.

Step 3: because the op-amp tries to minimize the difference between both input terminals, we give a reference from the non-inverting terminal to ground. This sets a reference line and the input is amplified by the same factor.

Adjustable amplifier with selectable gains

I made this DC gain amplifier which can be adjusted according to the input applied, and here you will find 3 different modes which set the gain 10x, 50x and 100x, so it is easy to amplify and test any DC signal out from any device. Gain can be selected by switching the jumper to a different position on the PCB.

#dc amplifier using opamp#