Hi,
I want to build a DC motor PWM speed controller, and I found on google a 555 timer circuit that does it.

1)R3 C3 and C4 are for decoupling the dc supply. what exactly is decoupeling? I know that resistor and capacitor are for frequency filters, so how it is related to the circuit?

2)Does the supply voltage needs capacitor for peak current? im using 12v and 5 amp dc supply.

3)About the spike diode,does repalcing D2 in zener diode that goes to ground is a better way?

4) C5 is for parasitic capacitance, how parasitic capacitance make problems? and how small capacitor solve that?

Thanks for helping!

 

Decoupling generally means removing a part of a circuit from the active section and ensuring it is common to either or both supply rails, IOW decouple it from any signal source.
Max.

 

Decoupling generally means removing a part of a circuit from the active section and ensuring it is common to either or both supply rails, IOW decouple it from any signal source.
Max.

Thanks for your answer! so why use large and small capacitor in parralel?

 

Large value capacitors tend to possess some inductive reactance as frequency increases.
The smaller value one provides a shunt or counteracts these such eventualities.
Max.

 

Thank you Max! it is more clear now