ENMODS™

Rev 3.3

vicorpower.com

Page 11 of 13

06/2017

800 927.9474

EN1xxx

Example

In this example, the output required from the DC-DC converter

power from the ENMods would be 375W (assuming a converter

efficiency of 85%). The desired hold-up time is 9ms over an input

Determining Required Capacitance for Power Fail Warning:

Figure 13 is used to determine capacitance for a given power

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

capacitance should be at least 820µF. Since two capacitors are

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

that warning time is not dependent on line voltage. A hold-up

capacitor calculator is available on the Vicor website, at:

www.vicorpower.com/powerbench/product-calculators.

Determining Ride-through Time: Figure 14 illustrates

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

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

Determining Ripple Voltage on the Hold-up Capacitors:

Figure 16 is used to determine ripple voltage as a function of

operating power and bus capacitance, and shows that the ripple

voltage across the hold-up capacitors will be 12Vp-p.

Determining the Ripple on the Output of the DC-DC

Converter: Figure 17 is used to determine the ripple rejection

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

approximately 60dB for a 12V output. Since the ripple on the

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

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

A variety of hold-up capacitor assemblies (HUBs) are available.

Please visit the Vicor website at:

www.vicorpower.com/powerbench/product-calculators.

For more information about designing an autoranging

AC input power supply using the ENMods and Vicor DC-DC converter

modules, contact Vicor Applications Engineering at the nearest Vicor Tech-

nical Support Center, or send 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.

Application Note (Cont.)

The power fail warning time (∆t) is defined as the interval

between BOK and converter shutdown (EN) as illustrated in

Figure 15. The Bus-OK and Enable thresholds are 205V and

190V, respectively. A simplified relationship between power fail

warning time, operating power, and bus capacitance is obtained

by inserting these constants in Equation (3):

It should be noted that the series combination (C1, C2, see

Figure 1a) requires each capacitor to be twice the calculated

value, but the required voltage rating of each capacitor is

reduced to 200V.

Allowable ripple voltage on the bus (or ripple current in the

capacitors) may define the capacitance requirement.

Consideration should be given to converter ripple rejection.

Equation 3 is again used to determine the required capacitance.

In this case, V1 and V2 are the instantaneous values of bus

voltage at the peaks and valleys (see Figure 15) of the ripple,

respectively. The capacitors must hold up the bus voltage for the

time interval (∆t) between peaks of the rectified line as given by:

The approximate conduction angle is given by:

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:

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 13, 14, and

16, respectively.

C = 2Pt / (5,925)

(4)

t = (π – θ) / 2πf

Where:

f = line frequency

θ = rectifier conduction angle

(5)

(6)

I

Where:

P = total output power

Vac = operating line voltage