Testing Power Factor Correction Circuits For Stability
Power factor correction has become an increasingly necessary feature in new
power supply designs. In a power factor correction circuit there are two
feedback control loops. One loop operates by using the input voltage as a
reference to control the input current. This loop is fast and makes the
input current instantaneously proportional to input voltage as it would be
with a resistive load. A second loop, which is much slower, controls the
constant of proportionality to make the average current correct to keep the
output voltage of the power factor correction circuit constant. Testing the
slow loop for stability is easy with the proper equipment, but testing the
faster loop is much more difficult. The operating point of the faster loop
is dynamically changing from near zero to the peak value of the input
current. This paper discusses the techniques necessary to measure the
stability of each of these loops and specifies necessary equipment and
procedures to perform these tests.
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