UG:107
vicorpower.com
Applications Engineering: 800 927.9474
Page 4
Technical Description
The 3 Phase MegaPAC and 4kW MegaPAC are configured by installing same length
ConverterPAC assemblies into the chassis. The chassis takes AC input power and
performs filtering and rectification functions. The ConverterPACs plug into a high-
voltage backplane and provide low-noise, independently regulated and fully isolated
outputs.
Input AC mains voltage (L1, L2, L3 and GND) is applied to an agency approved mating
plug. The input current is passed through an EMI filter designed to meet EN 55022 Level
A before it is passed to a three-phase full-wave bridge rectifier. The rectifier charges
storage capacitors and delivers unregulated 300 Vdc to a backplane after passing
through a large choke that improves input power factor. The power factor typically
exceeds 0.9 depending upon load, line voltage, frequency and line balance. Inrush
current is actively controlled with an IGBT and never exceeds 30A peak regardless of hot
or cold starts.
A housekeeping supply, isolated from the AC input, powers the brushless DC cooling
fan and other input monitoring circuits, in addition to providing an aux5V power
source for the user. The 4kW MEGAPAC HAS A SECOND FAN FOR EXTRA COOLING.
Excessive input currents caused by loss of a phase or excessive output loading in single
phase operation will safely shut down the unit until input power is recycled. This occurs
when the peak input current reaches 30A . An analog temperature monitor is provided,
as well as overtemperature shutdown. An active-high TTL compatible Enable control is
included for each ConverterPAC assembly, as well as an active-low General Shutdown
control; the polarities, active-high or active-low, are factory set. The 3 Phase MegaPAC
and 4kW MegaPAC can be safely paralleled (with another of its own kind) with accurate
current sharing for high power systems. All interface signals are safety isolated using a
common floating return.
Upon power-up, all outputs are first disabled to limit the inrush current, and to allow
the unregulated bus to reach correct operating levels for ConverterPAC assemblies. The
internal housekeeping supply comes up within 500 ms after input power is applied, and
the AC Power OK signal asserts to a TTL "1," indicating the input power is OK. The low
voltage power outputs come up within 10-20 ms after the AC Power OK asserts to a TTL
"1." Output ramp-up time from Enable or General Shutdown is 10-20 ms. Output fall
time from Disable is dependent on load, but is typically a few hundred microseconds.
Fuse
Isolated
Housekeeping
Power Supply
DC Brushless
Cooling Fan
EN 55022
Level A
3 Phase
Full-Wave
Rectifier
PFC Choke
IGBT
Opto-isolated
Control/Status
J10
Customer
Interface
J1
Input
Power
+P, -P
Output
Power
Remote Sense,
Trim Interface
Power Good
Interface
3 Phase/4kW MegaPAC Chassis
ConverterPAC (Up to 10)
DC/DC
Converter
Start-up Control
Circuits
Figure 1.
3 Phase MegaPAC and 4kW
MegaPAC Architectures
