A typical LED lighting circuit is shown in figure 1. For C1, C2, and C3 safety recognised capacitors should be selected that are rated AC 250Vrms. C6 is the snubber capacitor for the diode; parts rated to withstand DC 250V to DC 630V are needed and these can have X7R temperature characteristic.
It will also depend on the physical size requirement. The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V).
When sizing a capacitor, always choose one with a voltage rating higher than the maximum voltage in your circuit to prevent breakdown and damage. The capacitance value, measured in farads (F), indicates the amount of charge a capacitor can store for a given voltage.
The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V). So, the capacitor voltage rating should be 226.67V (170/0.75).
Overall, the conditions experienced by ceramic capacitors in LED lighting circuits should not be underestimated. It is my experience that selecting the wrong capacitor can adversely affect the lifetime of the end product due to crack formation in the dielectric material of these capacitors.
Some places recommend using 450uf 25V while others 1000uf 35V. Can someone explain in short what is the factors taking into account when choosing the capacitor value? My Setup OR In this case should it matter that the first power source is 12V ? where should I install the CAP? Thanks