Lowpassfilter

The fast switching of the mosfet induces voltages with higher frequencies in the whole circuit, which can distort the voltage measurement at the ADC. To filter out these frequencies and improve the signal, a simple low-pass filter is placed after the voltage divider, as shown in figure. The filter should have a cutoff frequency of about $f_c=75Hz$, for this the resistor $R_{filter}=10k\mathrm{\Omega }$ is determined first. Here $R_{filter}$ should be chosen in the same order of magnitude as the voltage divider, so that the capacitor $C_{filter}$ can be kept small. However, too large a value is also undesirable, otherwise the ADC will no longer be able to measure a signal.

$$\begin{array}{}\text{(1)}& C_{filter}=\frac{1}{2\pi R_{filter}{f}_c}=\frac{1}{2\cdot \pi \cdot 10k\mathrm{\Omega }\cdot 75Hz}=212.2nF\end{array}$$

The capacitor $C_{filter}$ is calculated according to $\text{(1)}$ and assigned to a suitable value of the E24 series with $C_{filter}=220nF$.

Lowpass filter