ESAB EPP-400 Manuel D'instructions page 106

sectIon 4
4.1 Block Diagram circuit Description (con't.)
The power circuit utilized in the EPP-400 is commonly referred to as a Buck Converter or a Chopper. High speed electronic
switches turn on and off several thousand times per second providing pulses of power to the output. A filter circuit, con-
sisting primarily of an inductor (sometimes called a choke), converts the pulses to a relatively constant DC (Direct Current)
output.
Although the filter inductor removes most of the fluctuations from the "chopped" output of the electronic switches, some
small fluctuations of output, called ripple, remain. The EPP-400 utilizes a patented power circuit combining the output
of two choppers, each providing approximately half the total output, in a manner that reduces ripple. The choppers are
synchronized so that when the ripple from the first chopper is increasing output, the second chopper is decreasing output.
The result is the ripple from each chopper partially cancels the ripple from the other. The result is ultra low ripple with a
very smooth and stable output. Low ripple is highly desirable because torch consumable life is often improved with low
ripple.
The graph below shows the effect of ESAB's patented ripple reduction using two choppers synchronized and switching
alternately. Compared to two choppers switching in unison, the alternate switching typically reduces ripple a factor of 4
to 10.
epp-400 output rMs ripple current versus output voltage
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6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
Choppers Synchronized and Switching in Unison (10KHz Ripple)
Patented EPP-400
Choppers Synchronized and Switching
Alternately (20KHz Ripple)
50 100
output voltage (volts)
150 200
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operatIon
250 300