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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
300V
DC
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 shut down. An active-high TTL compatible Enable control is
included for each ConverterPAC assembly, as well as an active-low General Shut Down 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 500ms 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 – 20ms after the
AC Power OK asserts to a TTL "1." Output ramp-up time from Enable or General Shut Down is
10 – 20ms. 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 ten)
DC/DC
Converter
Start-up Control
Circuits
Figure 1
3-Phase MegaPAC and
4kW MegaPAC Architectures
