文档介绍：Switching Power Supplies
Switching Power Supplies
The linear power supplies of the last set of notes work fine. However, the filter capacitors and 60Hz
power transformers result in considerable weight and expense. Furthermore, the series pass element in
the three pin linear regulator is a guaranteed energy loss. Switching power supplies, by operating at high
frequencies (such as 50kHz), eliminate much of the transformer and capacitive weight. Further, since the
series elements are switching off and on, spending little time in the linear regime, we find the efficiency
of the switching power supply is greater than linear power supplies. The penalty for the switching power
supply is greater plexity, and greater high frequency ripple and broadcast noise.
In general terms, switching power supplies are operated in either the buck configuration, where the load
voltage is less than the raw voltage, or in the boost configuration, where the load voltage is greater than
the raw voltage.
In the bucking configuration, the switching regulator provides power to the pass transistors for a variable
duty cycle, or for a variable frequency signal. The diode is a freewheeling diode to protect the switching
transistors from inductive kick, while the inductor and capacitor form a two pole low pass filter for the
output voltage.
In the boost configuration, the outpu