VI-ARM™

Rev 4.9

vicorpower.com

Page 9 of 11

06/2017

800 927.9474

VI-ARMx1xx

Operating Power (W)

0

5

10

15

20

25

30

1500

1250

1000

750

500

250

*

*

2,200 F

1,600 F

1,300 F

*

1,100 F

820 F

(VI-ARMB-x2)

Figure 17 — Ripple voltage vs. operating power and bus

capacitance, series combination of C1, C2

(see Figure 10)

Application Note (Cont.)

Output Voltage

40

45

50

55

60

65

70

75

80

50

30

15

5

2

Figure 18 — Converter ripple rejection vs. output voltage (typical)

Example

at 320W. Therefore, the output power from the ARM would be

375W (assuming a converter efficiency of 85%). The desired hold-

Determining Required Capacitance for Power Fail Warning:

Figure 15 is used to determine hold-up capacitance for a given

power fail warning time and power level, and shows that the total

bus capacitance must be at least 820µF. Since two capacitors are

used in series, each capacitor must be at least 1,640µF.

Note: The warning time is not dependent on line voltage. A hold-up

capacitor calculator is available on the Vicor website,

at

vicorpower.com/hubcalc.

Determining Ride-through Time: Figure 16 illustrates ride-

through time as a function of line voltage and output power, and

68ms. Ride-through time is a function of line voltage.

Determining Ripple Voltage on the Hold-up Capacitors:

Figure 17 is used to determine ripple voltage as a function of

operating power and bus capacitance, and shows that the ripple

Determining the Ripple on the Output of the

DC-DC Converter: Figure 18 is used to determine the ripple

rejection of the DC-DC converter and indicates a ripple rejection

of approximately 60dB for a 12 Volt output. If the ripple on the

60dB, the output ripple of the converter due to ripple on its input

(primarily 120Hz) will be 12mVp-p.

Note: Maxi, Mini, Micro converters have greater ripple rejection then either

VI-200s or VI-J00s.

For more information about designing an autoranging AC input

power supply using the ARM and Vicor DC-DC converter modules,

contact Vicor Applications Engineering at the nearest Vicor Technical

Support Center (see back cover), or send an E-mail to:

apps@vicorpower.com.

Storage

Vicor products, when not installed in customer units, should be

stored in ESD safe packaging in accordance with ANSI/ESD S20.20,

“Protection of Electrical and Electronic Parts, Assemblies and

Equipment” and should be maintained in a temperature controlled

factory/ warehouse environment not exposed to outside elements

controlled between the temperature ranges of 15°C and 38°C.

Humidity shall not be condensing, no minimum humidity when

stored in an ESD compliant package.

Another consideration in hold-up capacitor selection is their

ripple current rating. The capacitors’ rating must be higher than

the maximum operating ripple current. The approximate

operating ripple current (RMS) is given by:

(6)

I

Where:

P = operating power level

V

Calculated values of bus capacitance for various hold-up time,

ride-through time, and ripple voltage requirements are given

as a function of operating power level in Figures 15, 16, and

17, respectively.