# How capacitor values are determined in this circuit

I am following the course on control systems from edx. I have this circuit as part of practical exercise. I would like to understand how the capacitor values were determined in this circuit

1. The 47uF is for power supply filtering
2. The 47nf is for reduce the switching speed of PWM
3. The two 2.2uf capacitors for filtering noise signals from motor

The circuit is powered by arduino and the motor is powered by an external 5v 3A power supply. The lessons say that the motor can draw up to 2 A, If i assume the ripple voltage is 2 v and main freq is 60 hz, then the ripple frequency is 120 hz, the current that the capacitor can take/give is

$$I = C \frac{\Delta V}{\Delta T}$$

which gives 11.2 mA only

$$I = 47 \times 10^{-6} \times \frac{2}{\frac{1}{120}} = 11.2 mA$$

However the lesson says the motor can draw up to 2A how is this capacitor sufficient?

• The formula you used is for calculating value of a capacitor within a power source based on a transformer and full bridge rectifier. You don't need that formula. You are not building a power source, you already have one. And most likely it is smps type. – Chupacabras Dec 9 '18 at 7:48
• What is the role of 47uf capacitor here then? Why a value of 47uf was chosen – vumaasha Dec 9 '18 at 8:10
• It is a decoupling cap. Filters out some noise or minor glitches. – Chupacabras Dec 9 '18 at 9:19