*C2 creates a low-pass filter to stabilize the Arduino's ADC readings.
C1 = ΔIL / (8 * Fsw * ΔVout)
C2 = 1 / (2 * π * R_parallel * (Fsw/10))
Quick Start Guide
Define Your Rails: Enter your supply voltage ($V_{in}$) and your target output voltage ($V_{out}$).
Set the Load: Input the maximum current ($I_{out}$) your device will draw.
Choose Frequency ($f_{sw}$): For standard microcontrollers like the ATmega328P, a frequency between 20kHz and 60kHz is ideal to keep the inductor size manageable and avoid audible noise.
Select Ripple Factor ($K$): A value of 0.3 (30%) is the industry standard balance between component size and output stability.
Technical Cautions
A Buck converter is a "step-down" topology. The input voltage must always be higher than the output voltage plus the "dropout" voltage of your MOSFET (usually 1–2V higher) to maintain regulation.
When choosing a physical inductor, its Saturation Current ($I_{sat}$) must be higher than your $I_{out} + (\Delta I_L / 2)$. If the inductor saturates, it loses its "coil" properties and acts like a short circuit, which will likely blow your MOSFET.
Standard electrolytic capacitors may overheat at high switching frequencies. For professional results on ee-diary.net, always use Low-ESR capacitors or place a 0.1µF ceramic capacitor in parallel with your large electrolytic to filter high-frequency spikes.
Even with a low $R_{DS(on)}$ MOSFET like the IRF4905, switching losses can generate heat.
Ensure $Q2$ has adequate heatsinking if drawing over 2A.
Use a Schottky diode (like the 1N5822) for $D1$ because its low forward voltage drop significantly reduces heat compared to standard silicon diodes.
As we discussed with your schematic, always take your voltage feedback (for the Arduino analogRead) after the inductor and capacitor. Measuring before the filter will result in "garbage" data due to the high-speed PWM switching.