Today I dismantled a company’s LCD power meter. There is a voltage transformer to collect AC voltage signals, and a current transformer to collect AC current signals. One end of the two signals is connected to the AD sampling port of the microcontroller, and the other end is passed through an operational amplifier. I have received the AREF port of the microcontroller, but I can’t understand the principle of connecting the op amp. Please help me.
Micaela Posted on December 2, 2020
AREF is the reference voltage output by the chip, because the AC signal has a negative value to the ground, and the ADC cannot sample a negative voltage
So it needs to be biased
The reason for using an op amp is to isolate the level, because the reference voltage cannot be directly added to the signal.
So through the op amp isolation, two op amps are used to ensure the stability of the DC bias. Connecting the two op amps together is beneficial
Suppress drift.
AREF is connected to a resistor to the ground because it is necessary to provide a level to the ground for the non-inverting terminal, which can be understood with a single op amp.
Belen Posted on December 2, 2020
Hello, isn't AREF the reference voltage of the chip input? Do you mean that he outputs a bias voltage to raise the AC signal?
Iman Posted on December 2, 2020
Is the drawing wrong? Why is the input and output of the op amp directly short-circuited, and no components are used?
