Hello, Roger -- In early times, it was thought the "equalizing"
resistors might be a good idea. If all of the rectifiers in a
series-string have the same, measured PIV, equalizer resistors will
cause no harm. However, what if the rectifiers have different PIVs?
In your FWB power supply, the actual PIV across each of the 4-legs =s
the no-load V on the filter-C. -- which will probably be c. 2400v.,
Let's say that three rectifiers are used per leg, for a total of 12
rectifiers. 11 of the rectifiers measure 1000PIV and one of the
rectifiers measures 600PIV. Thus, one of the legs will have a total
PI-capability of 2600V and the other three legs will have a total
PI-capability of 3000V. Since the total PIV of the weak leg is not
exceeded during operation, no failure should occur. Next, add
"equalizer" resistors. This causes an equal 800v to be applied to each
rectifier. This causes no problem for the 1000piv units, but 800v
reverse causes the 600v rectifier to avalanche and short, which in turn
applies 1200v to each of the remaining 1000v rectifiers, which causes
them to short -- sort of like falling dominoes.
- note - the new ARRL Handbooks explain this problem - but in less
detail.
cheerz
On Sep 18, 2004, at 8:55 AM, Roger B wrote:
Hello to all
I am designing a 2kV PSU for a 1kW amp (bridge not
doubler).
About equalising resistors and capacitors with HV
diodes, some says it is absolutely necessary. Others
say it is a waste of time with modern diodes.
Any comment will be appreciated. 73 Roger
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