Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
VI-200 and VI-J00 Family Design Guide
Rev 3.4
vicorpower.com
Page 55 of 97
Apps. Eng. 800 927.9474
800 735.6200
OVERVIEW
Vicor’s FlatPAC consists of an offline single phase AC front
end and one, two or three VI-26x / VI-B6x Family DC-DC
converter modules (1-up, 2-up, 3-up), combined in an
integrated mechanical assembly. This assembly provides a
complete, high efficiency, offline switching power supply
delivering power up to 600 W. The offline front end
provides rectification and filtering of the AC input,
delivering a nominal unregulated 300 Vdc bus as input to
the VI-26x / VI-B6x Family converter modules. The front
end control circuit will automatically strap the bridge as a
voltage doubler for 115 Vac operation or as a full bridge
for 230 Vac operation.
CIRCUIT OPERATION
AC line voltage is applied via an agency-approved terminal
block providing AC mains (L1, L2/N and GND). Current in
the L1 lead is applied to a 15 A / 250 V fuse for the 3-up
FlatPAC, a 12 A / 250 V fuse for the 2-up FlatPAC and a
8 A / 250 V fuse for the 1-up FlatPAC. This current is
interrupted only in the event of a catastrophic failure
of a main power component internal to the FlatPAC.
The input current beyond the fuse is passed through an
EMC filter designed to meet conducted noise limits of
FCC Part 15 EN55022 Class B for the 2-up and 3-up
versions. At start-up, AC inrush current is limited by a
PTC thermistor prior to being passed to the main energy
storage capacitors. This PTC thermistor serves as both an
inrush current limiter on power-up and a current limiting
shutdown device in the event of a line overvoltage
condition. The PTC is shunted out shortly after initial
power-up by a pair of inverse parallel SCRs on the 3-up
FlatPAC (TRIAC for the 1-up and 2-up FlatPAC), controlled
by an opto-TRIAC coupler driven by a DC bus voltage
sense circuit. The main rectifiers and filter capacitors are
arranged in a conventional selectable configuration and
act as either a full wave bridge or voltage doubler,
delivering a nominal 300 Vdc to the converter modules.
At initial power-up, the front end is configured for 230 V
operation and the PTC inrush limiter permits the main
storage capacitors to charge up at a controlled rate
toward full operating DC bus potential. If the bus voltage
is below the operating threshold for the converter, the
unit will autostrap for 115 V operation. The autostrapping
function is performed by a control circuit and TRIAC (dual
SCRs on 3-up unit) which configures the front end from a
full wave bridge to a voltage doubler. Once the unit
autostraps for 230 V operation, it will be necessary to
recycle the AC power to allow operation at 115 V. If the
unit is operating in the 115 V mode and a long duration
transient is applied to the FlatPAC (>150 Vac for 50 ms),
the unit will autostrap for 230 V operation.
The control circuit maintains the converter GATE IN pins
low, the PTC shunt inactive and the AC-OK and BUS-OK
outputs in FAIL status until the DC bus potential reaches a
minimum threshold at which full power and hold-up can
be delivered. The GATE IN terminals of all Driver modules
internal to the FlatPAC are FET-controlled by a logical
replica of the BUS-OK status line, and as such will inhibit
converter operation at power-up until the DC bus potential
has settled to full operating level. The converters are then
enabled and the PTC shunt activated.
The AC-OK and BUS-OK status lines go to their respective
active states almost simultaneously on initial power-up.
AC-OK will de-assert prior to BUS-OK on loss of AC input,
providing advance warning of impending DC failure should
the AC line not return prior to the expiration of the ride-
through time (a function of both load and line voltage).
The front-end output is bled down automatically after loss
of AC input, as the logic circuit operating power is derived
from a bleed path across the DC output bus. Wait two
minutes before reapplying input after shutdown. Input
voltage to the converters is made via fast-acting 3 A / 250
V Buss PC-Tron fuses in each positive input lead. The fuse
will clear rapidly and protect the front-end from damage
in the event of a module input short.
Input overvoltage sensing and protection is performed by
a voltage sensing circuit connected across the DC bus. In
the event of an overvoltage condition, a SCR / PTC
combination will simultaneously disable the drive for the
TRIAC / SCR PTC shunt, disable the converters and apply a
load across the DC bus. Normal operation resumes when
the input voltage falls within the normal operating range
when operated from a 230 Vac source.
A Master Disable function is incorporated in the 2-up and
3-up FlatPAC (MOD DIS+, MOD DIS–). This optically
isolated input will disable the output of all converters
simultaneously. Applying a current to this input will
disable the converters. This disable current should be
limited to 30 mA maximum by an external control element.
FLATPAC AC-OK AND BUS-OK STATUS OUTPUTS,
MOD-DIS INPUT (2-UP AND 3-UP ONLY)
The BUS-OK and AC-OK outputs provide the user with
both an optically isolated status indication of the internal
DC bus condition and advance warning of pending DC
bus drop-out due to AC line loss. These outputs, in system
applications, can provide power supply status, switch in
(standby) backup sources or initiate “power-down”
sequences to save volatile memory contents in the event
of AC line loss. The MOD-DIS input is an optically coupled
18. AC Input Power System (FlatPAC Family)
Summary of Contents for VI-200 Series
Page 100: ......
