bufferoperational-amplifiervoltage
I am using an LM358 as a voltage follower, giving it a supply voltage of 6 volts and input voltage of 5V
At the output I am getting 4.5V. By applying different configurations of input voltage and supply voltage I observed that there should a difference of 1.5V between supply voltage (Vcc) and input voltage.(IN+.) I am not able to find the reason behind it.
No, no reason for them to be equal, so long as you observe the maximum (and minimum recommended) total voltage and keep inputs within the common-mode range.
The minimum common mode range is +/-11V with a +/-15V supply. With supplies +15 and -8 you will have a common mode range of +11/-4. The input will work in this range, in the follower configuration.
Certainly not. The current is guaranteed to be less than 60mA. It's a minimum of only 10mA and that's with a 15V supply. Use the output swing numbers. With a +/-15V supply it can supply +/-10V to a 2K load (5mA). It might be a bit less with a 22V supply compared to 30V, but probably in that range.
Voltage followers are prone to oscillation if the load is capacitive, otherwise this amplifier is compensated to be unity-gain (the way you are using it) stable.
LM358 is not a rail-to-rail output opamp. So it means it is not able to drive its outputs hard enough to reach the supply voltage. There will always be a voltage drop even when it saturates. This exists both on the high side and, to a lesser extent, low side.
See the datasheet to know the magnitude of this drop (which depends on the current you need on the output - the more you draw, the bigger the drop):
For the high side:
For the low side:
Best Answer
This is to be expected from the LM358.
The datasheet says that the output range is from 0V to V+ minus 1.5V.
This is the relevant section of the datasheet: