A small article to help budding engineers on taking a decision of supply and input voltages while using the operational amplifiers.


Unless you are hard core analog engineer, using an operational amplifier is always a nightmare for the e hardware engineers. The concepts need to be thoroughly understood if one has to use an operational amplifier. Many of the engineers depend on experts’ opinion or online tutorials and articles to use them. Of course, the datasheet is the biggest bible of all. Some of the tips and tricks for using operational amplifiers are given below for quick reference.

1. One of the major confusion for the hardware engineers is the power supply that can be given to the operational amplifier. For example, consider the most widely used operational amplifier 741. Consider the 741C operational amplifier from Texas Instruments; it has recommended operating conditions as shown in the snapshot. You can see that the maximum rating is ±18V. As per this rating, you give a single supply of +36V to positive terminal (PIN#7) and GND the negative terminal (PIN#4). You can also give +24V to positive terminal and -12V to the negative terminal. But the cases where we use with different voltages on positive and negative terminals are rare.

2. When you use the operational amplifier with for example of ±18V, i.e., +18V on positive terminal and -18V on negative terminal, then the input signal cannot be used beyond this range. The input and output ranges of the operational amplifier depends on the supply voltage given to operational amplifier.



3. As mentioned in the above point, the input and output depends on the supply voltage. You cannot have an input signal voltage equal to the supply voltage. Also, you will always get a lesser voltage at the output. The common mode voltage is the important specification that needs to be considered while deciding on the maximum voltage that can be applied at the input. Check the below circuit which is simulated with +36V single supply and input exceeding the common voltage of ±12V (24V). The output got saturated beyond the voltage of 24V. Remember that the operational amplifier here is used as voltage follower.