Losses in Energy Storage Elements
The non-ideal properties of filter capacitor at the output and
the inductor affect the performance of the circuit. The inductor
is not lossless because of the winding resistance and the core
loss. The model of the inductor can be changed to a series network
containing a resistor reflecting its losses and an inductor. Due
to the losses in the inductor, there is a slight reduction in
the output voltage and also a drop in the efficiency of the circuit.
Given a duty cycle and a steady input voltage, the output voltage
is has been obtained in the previous page as:
The average inductor current is the same as the average load
current. Then the average inductor current IL is:
If the internal resistance of the inductor is Rind,
the drop in output voltage is approximately:
The effect of the ESR of capacitor is to increase the ripple
content in output. From the previous page, the change in capactor
current from its higheest value to its lowest value is:
The worst-case increase in peak-to-peak ripple in output voltage
can be obtained by just adding the ripple due to ESR with the
previously obtained value. If ESR of capavitor be Rcap,
then
The actual peak-to-peak ripple would be less than the value stated
above.
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