Vicor PFC MegaPAC-HPEL Power Factor Corrected AC-DC Switchers - Manual (Page 4)

UG:119 vicorpower.com Applications Engineering: 800 927.9474 Page 4
n For power expansion, use booster ConverterPACs. Viewing the unit from the output
terminal side, always insert boosters to the right side of the driver.
n Do not use boosters as independent outputs. Disconnecting bus bars will damage
booster ConverterPACs.
n For booster arrays, do not remove busbars.
n Always ensure that output hex-nuts are properly torqued before applying power
to supply.
n Run the output (+/–) power cables next to each other to minimize inductance.
n Wait five minutes after shutting off power before inserting or
removing ConverterPACs.
n The MegaPACs does not have user serviceable components. They must be returned to
the factory for repairs. Contact Customer Service for a RMA number before returning
the unit. Do not attempt to repair or modify the power supply in any manner other
than the exchange of ConverterPACs as described in this Design Guide.
n Insert proper fault protection at power supply input terminals (i.e., a fuse).
n Use proper size wires to avoid overheating and excessive voltage drop.
n Never loosen the inner nut on a ConverterPAC.
n Verify output nuts are tight before powering up.
n FinQPACs require two slots each because of the larger heat sink attached to dissipate
the extra heat generated by the higher power Maxi module. Refer to Page 8 for more
information on which ConverterPACs can be used.
Technical Description
The PFC MegaPAC-EL and PFC MegaPAC-HPEL chassis consists of an offline single
phase, power factor corrected front end, EMI filter, cooling fan, low noise filters,
customer interface and associated housekeeping circuits. Input AC mains voltage
(L1, L2 and GND) is applied to a terminal block. The input current is passed through an
EMI filter designed to meet conducted noise limit A specifications of FCC Part 15,
VDE 0871, and EN55022 Class A. At start up, inrush current is limited by a PTC
thermistor. The PTC is shunted out shortly after initial power up by a DC bus voltage
Sense circuit driving a relay. After rectification, the input voltage is put through a boost
converter that keeps the AC input current sinusoidal and synchronized with the AC
input voltage (in compliance with EN61000). The boost converter delivers regulated
high voltage DC to the hold-up capacitors and backplane. The backplane supplies power
to a variety of ConverterPAC assemblies that provide the desired regulated outputs.
Voltage conversion in the output assemblies is achieved by Vicor’s family of Zero-
Current Switching (ZCS) DC-DC converters. These are forward converters in which the
main switching element switches at zero current. This patented topology has a number
of unique attributes: low switching losses; high frequency operation resulting in
reduced size for magnetics and capacitors; excellent line and load regulation;
wide adjustment range for output; low EMI/RFI emissions and high efficiencies.
At initial power up, the PFC MegaPAC-EL and PFC MegaPAC-HPEL outputs are disabled
to limit the inrush current and to allow the DC bus potential to settle out to the correct
operating level. A low-power flyback converter operating with PWM current-mode
control converts the high voltage DC bus into regulated low voltage to power the
internal housekeeping circuits and DC cooling fan. The internal housekeeping Vcc