Rms-to-dc converter tutorial

The datasheet of the AD tells about the two most important factors that should be taken into account to calculate the percentage of error that this IC will produce while measuring RMS value, they are. By observing the curves on the graph, we can observe that the frequency response is not constant with amplitude but the lower the amplitude you measure in the input of your converter IC, the frequency response drops, and in the lower measurement ranges at around 1mv, it suddenly drops a few kHz.

I assume now you can understand the rest values. NOTE: The frequency response curve and the table are taken from the datasheet. In simple terms, the crest factor is the ratio of the Peak value divided by the RMS value. For example, if we consider a pure sine wave with an amplitude of. You can clearly see that from the below image taken from wikipedia. The table below from the datasheet tells us that if the calculated crest factor is between 1 to 3, we can expect an additional error of 0.

The below schematic for the RMS converter is taken from the datasheet and modified according to our needs. As shown in the schematic, an input attenuator is used which is basically a voltage divider circuit to attenuate the input signal of the AD IC that is because the full-scale input voltage of this IC is mV MAX.

Now that we have clear some basic facts about the circuit let us begin the calculations for the practical circuit. Now if we put these values in an online voltage divider calculator and calculate, we will get the output voltage of 0. That is the output of the voltage divider circuit. That is the output voltage from the AD IC.

Now you can see that the above theoretical calculation and both the multimeter results are close, so for a pure sine wave, it confirms the theory. The measurement error in both the multimeter results is due to their tolerance and for demonstration, I am using the mains V AC input, which changes very rapidly with time.

At this point, I did not bother to use my hantek BL oscilloscope because the oscilloscope is pretty much useless and only shows noise at these low voltage levels.

For demonstration, a PWM signal is generated with the help of an Arduino. The voltage of the Arduino board is 4.

Now put these values in an online voltage divider calculator and calculate, we will get the output voltage of 0. In theory, a True-RMS multimeter will easily be able to calculate this theoretically calculated value right?

During this time, the inductor current will rise linearly. When the PWM signal is low, the power switch will turn off. The inductor voltage reverses in polarity because it will resist to a sudden change in current.

As a result, the diode will conduct. Then, the current path is described below. In my designs, I always use the RMS value to compute the component stress and power dissipation. Therefore, I can guarantee ample margin. This is the easiest part! As you can see on the buck converter circuit, the inductor is in series to the load. The load side is already a pure DC considering a very good control loop. Therefore, the DC current of the inductor is just equal to the load value.

The capacitor required is ten times smaller than that demanded by previous RMS to DC converter designs. Tags : Miscellaneous. You Might Also Like Miscellaneous. Powered by Blogger.