# Buffered Voltage Divider VS Differential(Subtractor) Opamp

I'm trying to understand which one of these circuits is the best choice for measuring 400VDC signal using a microcontroller . But at first look circuit number 1 makes more sense since it is giving the exact expected result but in application the first one or the second one might have its own advantages when taking into account parameters like CMRR , resistoral tolarences , the amount of the gain and its linearity .

So , with explanations I'm expecting your valuable suggestions , and of course I'm open to new ideas too .

Thanks ; simulate this circuit – Schematic created using CircuitLab

• Can you explain why you are considering these two circuits, and only these two circuits? What do you think are the advantages and disadvantages of them? – Elliot Alderson Jan 19 at 11:37
• I consider such circuits because Isolation buffers are needed for a low impedance output - MCU(ADC) connected measurements , and basically I'm asking the same question to figure out which one is the best or better idea of a clear and linear an analog output . – Burak Günay Jan 19 at 12:03
• Well, the second circuit is more complicated and more costly. So why did you even consider it in the first place? You said that the first circuit "made more sense" so I am wondering why you are even asking this question, and why you asked about such specific characteristics. You see, this would make a great exam question for an electronics course and I don't want to take away that learning experience from you. – Elliot Alderson Jan 19 at 12:08
• because Isolation buffers are needed for a low impedance output Explain and prove that that is needed. As your input voltage is 400 V the voltage divider can be made such that it has a relatively low output impedance, in your circuit it is now less than 5.1 k. For many ADCs the resulting error will be negligible compared to a 0 ohm output impedance. My point: you don't need an opamp/buffer until you have proven that you do. At the moment you're just assuming. For example, you haven't even mentioned what the actual input impedance of the ADC is. – Bimpelrekkie Jan 19 at 12:22
• the best choice That depends on your definition of "best", what are your criteria? What (do you think) are the disadvantages of either solution? What is important to you? Low component count? Accuracy? – Bimpelrekkie Jan 19 at 12:26