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PRELIMINARY

Vicor Corp. Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715

FARM, Filter/Autoranging Rectifier Module

Rev. 4.7

Page 7 of 12

Bus-OK (BOK) Pin. (see Fig. 11) The Bus-OK pin is

intended to provide early-warning power fail information and

is also referenced to the negative output pin.

Caution: There is no input to output isolation in the FARM. It is

necessary to monitor Bus-OK via an optoisolator if it is to be

used on the secondary (output) side of the converters. A line

isolation transformation should be used when performing scope

measurements. Scope probes should never be applied

simultaneously to the input and output as this will destroy the unit.

Filter. (see Fig. 12) An integral input filter consists of a

common mode choke and Y rated capacitors (line-ground)

plus two X rated capacitors (line-line). This filter

configuration provides common mode and differential mode

insertion loss in the frequency range between 100kHz and

30MHz as illustrated in Figure 6.

Hold-up Capacitors. Hold-up capacitor values should be

determined according to output bus voltage ripple, power fail

hold-up time, and ride-through time (see Fig. 13).

Many applications require the power supply to maintain

output regulation during a momentary power failure of

specified duration, i.e., the converters must hold-up or ride

through such an event while maintaining undisturbed output

voltage regulation. Similarly, many of these same systems

require notification of an impending power failure in order to

allow time to perform an orderly shutdown.

The energy stored on a capacitor which has been charged to

voltage V is:

(1)

Where:

C = capacitance

V = voltage across the capacitor

Energy is given up by the capacitors as they are discharged

by the converters. The energy expended

(the power-time product) is:

1

2

(2)

Where:

P = operating power

∆t = discharge interval

of

∆t

Rearranging Equation 2 to solve for the required

capacitance:

C = 2P

2

(3)

Application Note (continued)

+In

PC (Gate In)

PR (Gate Out)

–In

N

EMI GND

N/C

L

+

B OK

ST

EN

–

150k

15Vdc

Vicor DC-DC

Converter

Micro-

controller

Figure 10—Enable (EN) function

+In

PC (Gate In)

PR (Gate Out)

–In

N

EMI GND

N/C

L

+

B OK

ST

EN

–

Vicor DC-DC

Converter

Micro-

controller

15 Vdc

27kΩ

+5 Vdc

Secondary

referenced

Optocoupler DI pkg. 26106

Optocoupler SM pkg. 26109

Figure 11—Bus OK (BOK) isolated power status indicator

4.7nF

L1

4.7nF

N

EMI GND

N/C

L

+

B OK

ST

EN

–

.47µF

.099µF

330µH

Figure 12—Internal filter