Alamrg
Inductance of 1 foot of straight wire is not 15nH. According to this calculator:
www.consultrsr.com/resources/eis/induct5.htm
it is between 330nH for 0.1" Dia to almost 500nH for thin wires.
Large capacitors have large inductance. Bypassing them with film caps creates parallel resonant circuit (inductance + lossless cap) that tends to ring. It is always better to use bunch of smaller caps in parallel to further reduce already smaller inductance and to lower resistance (ESR).
There are better quality caps like slit foil type (used in Hypex kits - very expensive) where foil has cuts to prevent eddy currents and to lower inductance (losses).
Power supplies require large capacitance because they are unregulated. Regulated SMPS running at 100kHz is fast enough to response to any current demand at 20kHz in spite of small capacitors.
Inductance of 1 foot of straight wire is not 15nH. According to this calculator:
www.consultrsr.com/resources/eis/induct5.htm
it is between 330nH for 0.1" Dia to almost 500nH for thin wires.
Large capacitors have large inductance. Bypassing them with film caps creates parallel resonant circuit (inductance + lossless cap) that tends to ring. It is always better to use bunch of smaller caps in parallel to further reduce already smaller inductance and to lower resistance (ESR).
There are better quality caps like slit foil type (used in Hypex kits - very expensive) where foil has cuts to prevent eddy currents and to lower inductance (losses).
Power supplies require large capacitance because they are unregulated. Regulated SMPS running at 100kHz is fast enough to response to any current demand at 20kHz in spite of small capacitors.