ABSTRACT
The basic theory of the switching power supply has been known since the 1930s. Practical switch-mode power supplies (SMPSs) have existed since the 1960s, starting with components designed for other uses and thus poorly characterized for SMPS use. Early SMPS systems were running at very low frequencies, usually from a few KHz to about 20 KHz. Early SMPS designs justified the SMPS techniques for higher output power ratings, usually above 500 W.
