Rev 6.7

vicorpower.com

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06/2015

800 927.9474

FARMxxxx

Figure 9 — Offline Power Supply Configuration

OffLine 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 Vicor 300 V input 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 1000 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, see Fig. 9) for

proper (autoranging) operation. Metal oxide varistors, 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

hold-up capacitors are located more than 3 inches (75 mm)

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 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

pin (referenced to the –In) of the converter an opto-isolator

or isolated relay should be employed.

+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 KΩ, 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

APPLICATION NOTE (CONT.)