PRELIMINARY
Application Note (continued)
Off-Line Power Supply Configuration
The FARM maintains the DC output bus voltage between 250
and 370Vdc over the entire input voltage range, which is
compatible with Vicor 2nd Generation, 300V input converters as
well as 1st Generation VI-26x and VI-J6x DC-DC converters.
The FARM automatically switches to the proper bridge or
doubler mode depending on the input voltage, eliminating the
possibility of damage due to improper line connection. The
FARM1xxx is rated at 500W in the low range (90-132Vac
input), and 750W in the high range (180-264Vac input). The
FARM2xxx is rated for 750W and 1000W for the low and high
input ranges respectively. Either of these modules can serve as
the AC front end for any number and combination of compatible
converters as long as the maximum power rating is not exceeded.
Strap (ST) Pin.
In addition to input and output power pin
connections, it is necessary to connect the Strap pin to the center
junction of the series hold-up capacitors
(C1, C2, see Fig. 9)
for
proper (autoranging) operation. Gas tubes V1 and V2 provide
capacitor protection. The bleeder resistors
(R1, R2, see Fig. 9)
discharge the hold-up capacitors when power is switched off.
Capacitors C7 and C8 are recommended if the holdup capacitors
are located more than 3 inches from the FARM output pins.
Enable (EN) Pin.
(see Fig. 10)
The Enable pin must be
connected to the PC or Gate-In pin of all converter modules to
disable the converters during power-up. Otherwise, the
converters would attempt to start while the hold-up capacitors were
being charged through an unbypassed current limiting thermistor,
preventing the bus voltage from reaching the thermistor bypass
threshold, thus disabling the power supply. The Enable output
(the drain of an N channel MOSFET) is internally pulled up to
15V through a 150kΩ resistor.
A signal diode should be placed close to and in series with the
PC or (Gate-In) pin of each converter to eliminate the
possibility of control interference between converters.
The Enable pin switches to the high state (15V) with respect
to the negative output power pin to turn on the converters after
the power-up inrush is over. The Enable function also provides
input overvoltage protection for the converters by turning
off the converters if the DC bus voltage exceeds 400Vdc.
The thermistor bypass switch opens if this condition occurs,
placing the thermistor in series with the input voltage, which
reduces the bus voltage to a safe level while limiting input
current in case the varistors conduct. The thermistor bypass
switch also opens if a fault or overload reduces the bus voltage
to less than 180Vdc.
Holdup Box (HUB)
820µF
HUB820-S
2200µF HUB2200-S
2700µF HUB2700-S
3300µF HUB3300-S
1200µF HUB1200-S
1800µF HUB1800-S
C3
F1
+In
C10
PC (Gate In)
Vicor DC-DC
Converter
PR (Gate Out)
–In
R2
R3
C2
N
N
EMI GND
+
B OK
R1
C7* V1
C1
Z1
C9
Filter/Autoranging
ST
Rectifier Module
EN
N/C
L
–
FARM
C8* V2
D3
L
PE
Part
C1,2
C3–6
R1,2
V1,2
F1,2
D1,2
C7,8
*
Z1
C9
D3,D4
C10,C11
R3
Description
Holdup capacitors
4700pF
150kΩ, 0.5W
200V MOV
3A, PC Tron
Diode
Film Cap., 0.8µf
MOV
0.47µF
1N5817
.001µF
500Ω
Vicor
Part Number
see text
01000
00127-1503
20461-200
02178
00670
03040
26108
C4
D1
C5
F2
+In
C11
D2
D4
PR (Gate Out)
–In
PC (Gate In)
Vicor DC-DC
Converter
Sizing PCB traces:
All traces shown in bold carry significant
current and should be sized accordingly.
FARM1-xxx
N/ST/L 10A rms at 90Vac and 500W
4A DC at 190Vdc and 750W
+/– In
FARM2-xxx
N/ST/L 20A rms at 90Vac and 750W
+/– In
8A DC at 190Vdc and 1000W
Required if C1 & C2 are located more than
3 inches from output of FARM.
*
C6
To additional modules
Figure 9—Converter
connections
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
FARM, Filter/Autoranging Rectifier Module
Rev. 4.7
Page 6 of 12
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