Vicor Micro Family of DC-DC Converter - Manual (Page 38)

Design Guide & Applications Manual
For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies
Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com
Page 37 of 88
Apps. Eng. 800 927.9474 800 735.6200
8. Filter / Autoranging Rectifier Module (FARM)
+IN
PC (GATE IN)
PR
–IN
+IN
PC (GATE IN)
PR
–IN
Vicor DC-DC
Converter
R1
R2
C1
C2
V1
V2
D2
D1
C3
C5
C4
C6
F1
F2
Vicor DC-DC
Converter
To additional modules
C7**
C8**
FARM
Filter/Autoranging
Rectifier Module
N
EMI GND
N/C
L
+
BOK
ST
EN
–
Z1 C9
L
PE
N
R3
D4
C11
C10
D3
R4
F3 *
Vicor
Part Description Part Number
C1,2 Hold-up capacitors
C3-C6 4,700 pF (Y2 type) 01000
C7,8** Film Cap., 0.61 µF 34610
C9 0.47 µF 03047
C10,C11 0.001 µF
D1, 2 Diode 00670
D3, 4 1N5817 26108
F1, F2 Use recommended fusing for specific
DC-DC Converters
R1, 2 150 K Ω, 0.5 W
R3, 4*** 250 Ω
V1,2 220 V MOV 30234-220
Z1 MOV 270 30076
Sizing PCB traces:
All traces shown in bold carry significant
current and should be sized accordingly.
N/ST/L 10 A rms at 90 Vac and 500 W
+/– In 4 A DC at 190 Vdc and 750 W
FARM2-xxx
N/ST/L 20 A rms at 90 Vac and 750 W
+/– In 8 A DC at 190 Vdc and 1000 W
* See Agency Approvals on FARM data sheet.
** Required if C1 & C2 are located more than
3 in (75 mm) from output of the FARM.
***Not used with VI-260/VI-J60 Not used with VI-260/VI-J60
Figure 8–3 — Offline power supply configuration
OFF-LINE POWER SUPPLY CONFIGURATION
The FARM maintains the DC output bus voltage between
250 and 370 Vdc over the entire input-voltage range,
which is compatible with the Maxi, Mini, Micro 300 V
input converters as well as VI-260 family and VI-J60 family
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 500
W in the low range (90 – 132 Vac input), and 750 W in
the high range (180 – 264 Vac input). The FARM2xxx is
rated for 750 W and 1,000 W 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,
Figure 8–3) for proper (autoranging) operation. Metal-oxide
varistors, V1 and V2 provide capacitor protection. The bleeder
resistors (R1, R2, Figure 8–3) discharge the hold-up capaci-
tors when power is switched off. Capacitors C7 and C8
are recommended if the hold-up capacitors are located
more than 3 inches (75 mm) from the FARM output pins.
Enable (EN) Pin. (Figure 8-4) 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
un-bypassed 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
15 V through a 150 k
Ω 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 (15 V) 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
400 Vdc. 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 180 Vdc.
CAUTION: There is no input to output isolation in
the FARM, hence the –Out of the FARM and thus the
–In of the downstream DC-DC converter(s) are at a
high potential. If it is necessary to provide an external
enable / disable function by controlling the DC-DC
converter’s PC or GATE IN pin (referenced to the –In)
of the converter an opto-isolator or isolated relay
should be employed.