18. AC Input Power System (FlatPAC Family)

18. AC Input Power System (FlatPAC Family)
Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
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.
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.
VI-200 and VI-J00 Family Design Guide
Page 55 of 98
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 ridethrough 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.
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
Rev 3.5
Apps. Eng. 800 927.9474
800 735.6200
18. AC Input Power System (FlatPAC Family)
Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
input and allows for remote disabling of the outputs of
2-up and 3-up FlatPACs.
BUS-OK. An internal replica of BUS-OK is wired to the
GATE IN input of all internal Driver modules. The modules
will be disabled (no DC output) during initial power-up of
the FlatPAC until the internal DC input bus voltage to the
DC-DC converters is sufficient to support fully-loaded
operation. The BUS-OK status output reflects the status of
this inhibit function. This same logic circuit will shut down
the converters when the internal DC bus voltage is
insufficient to support proper loaded operation. This shut
down will occur during normal power down, AC line
dropouts of duration exceeding the hold-up time, or
internal faults causing the internal DC bus voltage at the
input of the converters to collapse.
AC-OK. This output is provided primarily as an advance
warning of a potential DC BUS-OK shut down due to loss
of AC line or an internal fault. A minimum advance
warning time of 5 ms is provided at 90 Vac and full load.
detect assertion of logic outputs, or a separate source of
bias supply voltage (i.e., backup batteries) to provide a
safe pull-up voltage source regardless of the AC line status.
AC Mains
The Module Disable function will disable the output(s) of
the 2-up and 3-up FlatPACs. The supply is disabled by
applying current to the MOD-DIS+ / MOD-DIS– input. The
minimum input current for disabling the supplies is 1 mA.
The maximum allowable current is 30 mA.
NOTE: Product is internally fused
Figure 18–1 — AC mains and supervisory connections
AC-OK and BUS-OK Status Outputs. Outputs low when
OK. Vce sat. = < 0.4 V @ 1.5 mA. Maximum external
pullup is 70 Vdc. AC-OK and BUS-OK signals are isolated
and can have different reference levels.
30 mA max.
Status output pairs AC-OK+, AC-OK– and BUS-OK+,
BUS-OK– are the collectors (+) and emitters (–) of NPN
optoisolator output transistors (one optoisolator per status
signal). The collector terminals AC-OK+ and BUS-OK+ of
the optocouplers, in a typical application, can be
connected via current limiting resistors to a source no
greater than 70 Vdc. These resistors should limit the
maximum current to the optocoupler output transistors to
1.5 mA. The emitter terminals AC-OK– and BUS-OK– are
connected to the return of the external source. The status
OK condition will set the optocoupler output transistors in
saturation and are capable of sinking up to 1.5 mA with a
Vce saturation voltage of 0.4 V. Users should be cautioned
that although the output of the FlatPAC can be used as
the pull-up source, shortly after BUS-OK changes from OK
(saturated) to NOT OK (high Z), the pull-up voltage will be
shut down. It is thus advisable to provide a capacitive
reservoir, if the pull-up source is one of the FlatPAC’s
outputs, in order to maintain the pull-up potential after
loss of DC current output. Use edge sensing logic to
Page 56 of 98
Earth Ground
MOD-DIS Input. Apply a current of 1 – 30 mA to disable
output. Forward voltage drop of internal opto diode is
1.65 V max. at 30 mA max.
VI-200 and VI-J00 Family Design Guide
1.5 mA
1.5 mA
Figure 18–2 — External supervisory functions (2-up and 3-up
models only)
Rev 3.5
Apps. Eng. 800 927.9474
800 735.6200
18. AC Input Power System (FlatPAC Family)
Design Guide & Applications Manual
For VI-200 and VI-J00 Family DC-DC Converters and Configurable Power Supplies
Input Voltage Connections. Connect the line voltage
to L1 (hot) and L2N (neutral). For 1-up FlatPAC models
(max. output 200 W), use #16 AWG input wire; for 2-up
and 3-up models (max. output 400 W and 600 W), use #14
AWG input wire. Recommended connector screw torque is
5 to 7 in-lbs (0.5 to 0.8 N-m). Recommended strip length is
8 mm. Use your FlatPAC model only with the corresponding
input voltages and frequencies shown in the table below.
VLINE > 90 (180)Vac
AC Line
T0 T1
Conditions: Full Load 90 (180)Vac, AC Line
Time Interval
Units Notes
T1 – T0
T3 – T2
Ride-through time
T4 – T2
T4 – T3
Hold-up time
AC fail warning time
Figure 18–3 — Timing diagram – status signals (2-up and 3-up
models only)
R1 (KΩ)
R2 (KΩ)
15 V 24 V
28 V 48 V
0.953 15.8
22.1 41.2
90.9 +10%, –10%
90 +10%, –10%
Figure 18–4 — Output SENSE and TRIM (all models with VI-200s)
Programmable Current
or Voltage Source
12 – 48 V
Figure 18–5 — Typical applications (models with BatMods only)
Fusing. The FlatPAC’s internal fuses are not user-replaceable.
Please return the unit to vendor if servicing is necessary.
Grounding. To satisfy IEC950 Class I grounding requirements,
connect a ground lead to the terminal marked
For 1-up FlatPAC models (max. output 200 W), use 1.5 mm 2
/ #16 AWG wire; for 2-up and 3-up models (max. output
400 W and 600 W), use 2.5 mm 2 / #14 AWG wire.
VI-200 and VI-J00 Family Design Guide
Page 57 of 98
90 – 132 Vac
180 – 264 Vac
47 – 63 Hz
47 – 440 Hz
47 – 63 Hz
47 – 440 Hz
Output Wire Gauge. Use the output wire gauge that
corresponds to the output current of your Autoranging
FlatPAC unit, below: Do not loosen bottom nut.
Long cable runs, or wires in large bundles will require
heavier cable to avoid excessive voltage drops or overheating.
Resister Values for Trimming Standard Output Voltages
12 V
100 A – 160 A: #2 AWG 30 A –50 A: #8 AWG 10 A –15 A: #14 AWG
75 A –100 A: #4 AWG 20 A –30 A: #10 AWG 6 A – 10 A: #16 AWG
50 A – 75 A: #6 AWG
15 A –20 A:#12 AWG 0 A – 6 A: #18 AWG
NOTE: +SENSE and –SENSE must be connected locally or
remotely (shown).
Nom. Output
Product Grade
Output Voltage Trimming. Do not trim the outputs
higher than 110% of their nominal output voltage. When
an output is trimmed up, do not exceed its maximum
rated output power. (refer to Section 5)
Operating Temperature. Do not allow the FlatPAC to
exceed its maximum operating temperature, which is
reached when the heat sink is 85°C. (Full power can be
delivered up to this temperature.) Heat sink temperature is
a function of the output power and voltage of the supply,
ambient temperature, and airflow across the heat sink.
Always use worst-case conditions when calculating
operating temperature.
NOTE 1: To ensure proper heat transfer from the
internal module(s) to the heat sink, the mounting
holes through the heat sink (two, three, and four
holes on 1-up, 2-up, and 3-up models, respectively)
must contain torqued screws at all times during
operation, whether or not the unit is mounted. If the
unit is operated unmounted, insert a #6 or M3.5
panhead screw through each hole from below and
secure with a nut on top, torqued to 6 in-lbs (0.7 N-m).
NOTE 2: All FlatPAC models are available with a
conduction cooled flat plate instead of the top heat
sink. Go to vicorpower.com for outline drawings.
Input / Output Retrofit Connections. A hardware kit,
available from Vicor, allows the input and output
supervisory terminals to be connected in the same manner
as for the earlier style FlatPAC (2-up model only). The
retrofit output terminals are sized to accept AMP Faston®
insulated receptacle #2-520184-2.
Rev 3.5
Apps. Eng. 800 927.9474
800 735.6200