In battery operated power converters such as motor controller ( half bridge or full bridge ) bulk capacitance is placed across Vdd and Gnd . I thought this was unnecessary since the input is DC and batteries can be considered as "big capacitors" . But after reading i found some of the reasons are :
a. Provide energy in case of high current draw at start , and absorb energy at stop (generated by inductive load).
b. Reduce Ripple current which causes overheat and over voltage .
- Is there any more reasons ? which is more important ripple current specification or capacitance ?
For example : Assume there is a system that uses 1500uF capacitors with 3.3 A ripple current ,17mohm impedance at 100khz . The same company provides 560uF Capacitor with 2.18A ripple current 20mohm impedance at 100khz.
if two of 560uF are paralleled we will get roughly 1100uF with 4A ripple current , is this better or worse than a single 1500uF in the case of a motor controller ??
if Ripple current is more important than capacitance then what about using Film (Polypropylene) capacitors since they have very tempting characteristics. But they will have much lower capacitance about 15uF but current rating of 10A or more ?